Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session M1: Poster Session II (11:15am - 2:15pm)Poster
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Room: Exhibit Hall J |
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M1.00001: POLYMER PHYSICS |
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M1.00002: Classes of morphology of wrinkle patterns in floated polymer Jooyoung Chang, Narayanan Menon, Thomas Russell We have investigated capillary wrinkling on different types (PS, PMMA, and Poly(perfluorobutenylvinylether) known as Cytop\texttrademark ) and thicknesses (10 nm to 1 $\mu $m) of polymer films floated on water. As in our previous work (\textit{Science }2007, 317(5838), 650-653), a radial wrinkle pattern is induced by a water droplet placed at the center of the floated film. We have now varied the thickness of the film over a larger range than in our previous work, and we observe three distinct types of the wrinkle patterns, regardless of the material used. In the thinnest films, there appear to be two distinct Fourier modes throughout the wrinkle pattern; in intermediate thickness films, there is a single mode in the bulk of the pattern, which shows a cascade to a harmonic of this mode at the contact line of the drop (\textit{Soft Matter}, 2013, 9, 8289-8296); finally, for the thickest films the single mode persists throughout the pattern. Furthermore, we measured the observed wavenumber (N) of the wrinkles against bendability ($\varepsilon )$ of the polymer films; N was found to be proportional to the $\varepsilon ^{\mathrm{-1/3}}$ for the intermediate thickness but crosses over to the $\varepsilon^{\mathrm{-1/4}}$ for the thickest films. [Preview Abstract] |
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M1.00003: Single Gyroid Nanostructure from Templated Electroless Plating Using Double Gyroid-Structured Block Copolymer Template Kai-Chieh Yang, Cheng-Thai Yao, Rong-Ming Ho Here, we aim to suggest a novel approach for the fabrication of metallic materials with single gyroid (SG) texture using double gyroid (DG)-structured polymer template through the control of nucleation and growth mechanism. Nanoporous polystyrene (PS) with DG texture is prepared from the self-assembly of polystyrene-b-poly(L-lactide) (PS-PLLA) followed by hydrolysis of PLLA block, and then used as a template for templated electroless plating. With the introduction of Pd ion solution to the PS template, homogeneously distributed Pd within the PS template can be prepared by using hydrazine for the reduction of Pd ions, giving Pd nuclei for the growth of SG-structured Ni from the reduction of Ni ions. Subsequently, the Ni deposition using the Pd nuclei as catalytic site can be carried out to form SG-structured Ni. Nanoporous Ni with SG-structured texture can be obtained after removal of the PS template by washing with dichloromethane. With this novel approach, SG-structured Ni with controlled particle radius from hundreds nm to micrometer can be prepared by tuning the growth time for the Ni deposition. [Preview Abstract] |
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M1.00004: Abstract Withdrawn
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M1.00005: ``Effect of Polyalkylthiophene Microstructure on Physical and Optoelectronic Properties'' Michael J. Minkler Jr., Bryan S. Beckingham Conjugated polymers have been of widespread interest as flexible semiconductors for organic electronic devices such as solar cells, field effect transistor,s and light-emitting diodes. Of particular interest have been alkyl-substituted polythiophenes due to their well-controlled synthesis, favorable optoelectronic properties, and solubility in organic solvents. Importantly, relatively small changes to the chemical microstructure in poly(3-alkylthiophenes) (P3ATs) can have a significant effect on the resulting physical and optoelectronic properties. For instance, the addition of aliphatic side chains onto unsubstituted polythiophene provides solubility but also greatly decreases conductivity in comparison to unsubstituted polythiophene (PT). In this work, we use Grignard metathesis polymerization to synthesize poly(3-hexylthiophene) (P3HT), PT, and statistical copolymers (P[3HT-co-T]) over a range of compositions. We examine the physical properties (melting temperature, crystallinity, etc) by differential scanning calorimetry and wide angle X-ray scattering, optoelectronic properties by UV/Vis spectroscopy, and solubility in organic solvents of these copolymers in order to gain insights into the interplay of microstructure and properties in this class of materials. [Preview Abstract] |
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M1.00006: Kinetically Controlled Self-Assembly of Hierarchical Nanostructures Based on Block Copolymer Patchy Particles Jee Young Lee, Karen Wooley, Darrin Pochan Amphiphilic block copolymers have attracted much attention due to easily tunable morphologies from solution or melt assembly. In particular, they are able to self-organize into various nanostructures in solution based on solvent quality and block chemistry relative volume fraction. Recently, groups have used kinetic pathway to form kinetically trapped nanostructures far removed from classic micelle or membrane structure. Building on our previous studies on kinetically trapped patched micelles, we have further tailored the assembly by introducing functionalized nanoparticles to the system. Specifically, we take advantage of click-like ligation chemistry that allows rapid site-specific covalent attachment of partially functionalized patchy micelles to other polymer or inorganic nanoparticles. These patchy micelles, metastable structures with final morphologies that are highly dependent on assembly pathways, allow us to explore variety of kinetically trapped nanostructures and to use these as building blocks. We control the kinetic pathway by adjusting solvent conditions with time as well as by complexing hydrophilic, polyacid blocks of the polymer with organic amines. Cryogenic TEM is used to monitor structure formation in situ. [Preview Abstract] |
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M1.00007: Semi-Crystalline/Amorphous Polymer Blend Films Formed by MAPLE Yucheng Wang, Mithun Chowdhury, Hyuncheol Jeong, Rodney Priestley An enabling film processing method, termed Matrix Assisted Pulsed Laser Evaporation (MAPLE), is employed to investigate the morphology and thermal properties of polymer blend systems comprising both miscible and immiscible pairs: poly(ethylene oxide) (PEO)/ poly(methyl methacrylate) (PMMA) and polyethylene (PE)/PMMA. This novel technique holds an intrinsic uniqueness in that it features ultra-slow deposition rate, thereby allowing the simultaneous film growth and crystallization of molecules atop a temperature controlled substrate. In this work, the effect of substrate temperature as well as growth rate on film structure and thermal properties are probed with the aid of morphological, calorimetric, and scattering characterizations. Compared with solution casted films, variances sourced from the new approach help to understand the functionality of an existing amorphous polymer in semi-crystalline/amorphous binary systems, especially regarding the impact on melting point differentiation and change of crystalline structures. [Preview Abstract] |
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M1.00008: Self-assembly of coiled coil peptides into nanoparticles vs 2-d plates: effects of assembly pathway Kyunghee Kim, Darrin Pochan Molecular solution assembly, or self-assembly, is a process by which ordered nanostructures or patterns are formed by non-covalent interactions during assembly. Biomimicry, the use of bioinspired molecules or biologically relevant materials, is an important area of self-assembly research with peptides serving a critical role as molecular tools. The morphology of peptide assemblies can be controlled by adjusting solution conditions such as the concentration of peptides, the temperature, and pH. Herein, spherical nanostructures, which have potential for creating an encapsulation system, are formed by self-assembly when coiled coil peptides are combined in solution. These peptides are homotrimeric and heterodimeric coiled-coil bundles and the homotrimer is connected with each of heterodimer through their external surfaces via disulfide bonds. The resultant covalent constructs could co-assemble into complementary trimeric hubs, respectively. The two peptide constructs are directly mixed and assembled in solution in order to produce either spherical particles or 2-d plates depending on the solution conditions and kinetic pathway of assembly. In particular, structural changes of the self-assembled peptides are explored by control of the thermal history of the assembly solution. [Preview Abstract] |
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M1.00009: Quantifying lithium salt distributions in nanostructured ion-conducting polymer domains: a neutron reflectivity study Cameron Shelton, Joseph Dura, Thomas Epps Measuring the distribution of lithium salts in block polymer (BP) electrolyte thin films with high resolution and limited film damage is key to understanding ion-transport kinetics and improving the efficiency of lithium battery membranes. In this work, we quantified the distributions of three common lithium salts within the ion-conducting poly(oligo(oxyethylene)methacrylate) (POEM) block of a lamella-forming polystyrene-POEM (PS-POEM) thin film by exploiting the polymer-polymer and polymer-salt contrast gained from nondestructive neutron reflectivity (NR). As the salt-doping ratio in the POEM domains increased, multilayer Bragg peaks in the NR profiles disappeared gradually due to decreasing NR contrast between the PS and POEM/salt domains; this behavior was indicative of an even lithium salt distribution in the POEM domains. Furthermore, fitting the NR profiles to lamellae models produced through-film salt distribution profiles that denoted a diminishing concentration of salt from the substrate to free surface. Overall, the high-resolution, non-destructive benefits of using NR to investigate BP electrolyte thin films provided conclusive details related to the distribution of lithium salts, which directly affects their material properties and performance. [Preview Abstract] |
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M1.00010: Determination of Neutral Solute Permeabilities and Membrane Selectivities through PPO/PAGE Copolymer Membranes via \textit{in situ} ATR FTIR Spectroscopy? Breanna M Dobyns, Bryan S Beckingham Polymeric membranes are used in a wide range of applications, from biomedical applications to industrial separations to fuel cells. Solute permeability and selectivity are of fundamental interest when considering a membrane material for a particular application. Here, we examine the transport of aqueous species through neutral polymer membranes. We synthesize copolymers of varying composition of poly(allyl glycidyl ether) (PAGE) and poly(propylene oxide) (PPO) via potassium alkoxide initiated anionic ring opening polymerization. The physical properties of these copolymers can be tuned through the relative composition and the pendent allyl group in PAGE affords the inclusion of additional functionalities via click-chemistry techniques and crosslinking via UV-irradiation. The copolymers are pressed into membranes and cross-linked prior to hydration and placement in a custom-built diffusion cell outfitted with Attenuated-Total-Reflectance Fourier Transform Infrared spectroscopy. We report solute permeabilities of methanol, isopropanol, and acetone through these membranes and the calculated binary selectivities of these components. Lastly, we conduct multicomponent experiments and compare the selectivities and permeabilities to the single component experiments. [Preview Abstract] |
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M1.00011: Effect of Gel Microstructure on the Cavitation Instability Santanu Kundu, Satish Mishra, Mahla Zabet, Seyedmeysam Hashemnejad, Brandon Yrle Polymeric gels are widely used in many applications. Elastic modulus of a gel is directly related to its microstructure and the fracture behavior of a gel also depends on the microstructure. We report the non-linear rheology and cavitation rheology results for two self-assembled gels: pluronic gels consisting of poly(ethylene oxide)--poly(propylene oxide)--poly(ethylene oxide) in an end block selective solvent (water), and ABA triblock copolymer gels consisting of poly(methyl methacrylate)--poly(n-butyl acrylate)--poly(methyl methacrylate) in a mid-block selective solvent (2-ethyl- 1-hexanol). For the gels with similar low-strain modulus, distinctly different non-linear rheological behavior was observed, as pluronic gel strain-softens, whereas, triblock gel strain- stiffens at large-strain. The cavitation rheology data indicate that the critical pressure for cavitation in triblock gel is higher than that observed in pluronic gels. These results will be linked to the gel microstructure. [Preview Abstract] |
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M1.00012: Mechanical Properties of Stable Glasses Using Nanoindentation Sarah Wolf, Tianyi Liu, Yijie Jiang, Keyume Ablajan, Yue Zhang, Patrick Walsh, Kevin Turner, Zahra Fakhraai Glasses with enhanced stability over ordinary, liquid quenched glasses have been formed via the process of Physical Vapor Deposition (PVD) by using a sufficiently slow deposition rate and a substrate temperature slightly below the glass transition temperature. These stable glasses have been shown to exhibit higher density, lower enthalpy, and better kinetic stability over ordinary glass, and are typically optically birefringent, due to packing and orientational anisotropy. Given these exceptional properties, it is of interest to further investigate how the properties of stable glasses compare to those of ordinary glass. In particular, the mechanical properties of stable glasses remain relatively under-investigated. While the speed of sound and elastic moduli have been shown to increase with increased stability, little is known about their hardness and fracture toughness compared to ordinary glasses. In this study, glasses of 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene were deposited at varying temperatures relative to their glass transition temperature, and their mechanical properties measured by nanoindentation. Hardness and elastic modulus of the glasses were compared across substrate temperatures. After indentation, the topography of these films were studied using Atomic Force Microscopy (AFM) in order to further compare the relationship between thermodynamic and kinetic stability and mechanical failure. [Preview Abstract] |
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M1.00013: Chirality Effect on Self-Assembly of Chiral Triblock Copolymer Hsiao-Fang Wang, Po-Ting Chiu, Rong-Ming Ho A series of triblock copolymers composed of a chiral segment, poly(L-lactide) (PLLA), (referred as chiral triblock copolymers) is synthesized. Starting with a diblock, addition of asymmetric amounts of the chiral block to a symmetric diblock creates competing packing constraints. A smaller additional block should favor a finite spontaneous curvature while the equal-sized diblocks prefer a flat interface. With the introduction of chiral block that drives twisting of the flat interface, the curvature at the saddle surface becomes significant. Consequently, a transformation from two-domain lamellae to cylinder phase can be found in the isopleths of triblock, reflecting chirality effect on the self-assembly of the chiral triblock copolymers. Accordingly, the chirality effect will lead the helical steric hindrance at the interface of achiral and chiral blocks to give the microdomain with large curvature, giving the potential to create network nanostructure from self-assembly. [Preview Abstract] |
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M1.00014: Simulations of Indentation on a Polymer Thin Film and Properties Analysis Wenlu Shi, Graham Cross Using finite element simulation, we have verified for the case of that uniform uniaxial strain deformation test is independent of the geometric properties. A simple elastic-plastic material for aspect ratios as high as 12:1, the stress vs. strain behavior consists of a linear elastic region, a linear plastic region and a extrusion region is also verified. A new way to find extrusion point (wall failure) comes up, using the analysis of the changing of inner part volume. [Preview Abstract] |
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M1.00015: Complex Cure Kinetics of the Tertiary Amine activated Reaction in DGEBA Epoxy Hardened with Diethanolamine Windy Ancipink, John McCoy, Caitlyn Clarkson, Jamie Kropka, Mathias Celina, Nicholas Giron, Lebelo Hailesilassie, Narjes Fredj The curing of a diglycidyl ether of bisphenol-A (DGEBA) epoxy with diethanolamine (DEA) involves a well understood fast amine-epoxide reaction followed by a more complicated slower hydroxyl-epoxide reaction. The time scale of these two reactions are well separated and can be studied independently from one another. The initial amine-epoxide reaction results in a tertiary amine adduct which is a product of the direct reaction of a secondary amine from the DEA reacting with a single DGEBA epoxide. The second hydroxyl-epoxide reaction results in a highly crosslinked glassy epoxy resin. The deviation in the mechanisms between high and low temperatures are discerned through the use of differential scanning calorimetry (DSC), infrared spectroscopy (IR), and isothermal microcalorimetry (IMC) data. Observations of reaction rates at temperatures ranging from 30$^{\circ}$ C to 110$^{\circ}$ C have led to the determination that the hydroxyl-epoxide reaction is temperature sensitive. The hydroxyl-epoxide reaction occurs through two different mechanisms: at low temperatures, the reaction is catalyzed by the tertiary amine adduct; at higher temperatures, the reaction does not appear to be catalyzed. [Preview Abstract] |
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M1.00016: Gradient hydrogel coatings for medical applications Pandiyarajan Chinnayan Kannan, Jan Genzer Mussel byssus is a typical example for gradient material that demonstrates a continues variation in mechanical property (or modulus), $i.e.,$ soft (proximal) part is connected to mussel, while the stiffer (distal) part facilitates the attachment of mussel to a stone. Mimicking such materials is highly demanding especially in the areas of artificial implants. We developed a simple synthetic route to produce gradient hydrogels that are covalently anchored to the substrate. N-isopropylacrylamide has been copolymerized with 5 mole{\%} of photo-active (methacrylyloxybenzophenone) and/or 5{\%} of thermally-active (styrenesulfonylazide) crosslinkers. The incorporation of photo and/or thermal crosslinkers allows us for a complete control over the network properties in orthogonal directions. A systematic investigation towards the gel kinetics, swelling, crosslink density, elasticity and protein adsorption was performed. Our results instigate that weakly crosslinked (low modulus) gels swell strong in aqueous medium than the densely crosslinked (high modulus) gels. The results of protein adsorption are discussed based on the previously developed model entropic shielding and size exclusion effect. [Preview Abstract] |
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M1.00017: Mesoscale Simulations of pH-Responsive Swelling of Polyelectrolyte Complexes Shiyi Qin, Xin Yong Using dissipative particle dynamics (DPD), we model the swelling behavior of polyelectrolyte complexes formed by two oppositely charged linear polymers while changing the ionization of cationic polyelectrolyte according to the Henderson-Hasselbalch equation. The electrostatic interactions are solved using a modified Particle-Particle-Particle-Mesh (PPPM) method, which implements an iterative Poisson solver. We characterize the formation of the complex from two separated chains and elucidate the influence of ionization of the cationic polyelectrolyte on the morphology of the complex. The radial distribution functions and the radius of gyration of each polyelectrolyte are calculated to quantify the conformational changes. We find that the complex swells and shrinks depending on the degree of ionization and subsequently correlate the swelling ratio with the pH value. We further reveal the effects of the polyelectrolyte sizes, the concentration of monovalent salts on the swelling behavior of polyelectrolyte complexes. [Preview Abstract] |
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M1.00018: Controlling the morphology of immiscible polymer blends using bottlebrush random copolymers Huizhen (Adeline) Mah, Pantea Afzali, Luqing Qi, Stacy Pesek, Rafael Verduzco, Gila Stein Bottlebrush polymers are highly branched macromolecules with polymeric side-chains attached to a linear backbone. The functionality and properties of the bottlebrush is controlled by the side-chain composition, side-chain length, and backbone length. In this study, we investigate the thin film phase behavior of a ternary blend system consisting of polystyrene (PS) and poly (methyl methacrylate) with 20 wt{\%} of a bottlebrush poly (styrene-r-methyl methacrylate) additive. The blend morphologies were characterized using atomic force microscopy and optical microscopy. We find that bottlebrush poly (styrene-r-methyl methacrylate) additives having 50-60 mol{\%} styrene are soluble in the PS phase, reaching a concentration of 20 vol{\%}, but limited miscibility with PMMA can drive the formation of a PMMA/bottlebrush interphase. This interphase inhibits the coarsening of microstructures while forming a co-continuous network. [Preview Abstract] |
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M1.00019: Composition, functionality and topology effect on the self-assemble behaviors of PS-POSS conjugates. Stephen Cheng, Wei Zhang We have designed a synthetic strategy to allow us to attach the ``nanoatoms'' on to a polystyrene (PS) chain with controlled heterogeneity. The ``nanoatoms'' used here are polyhedral oligomeric silsesquioxanes (POSS). The heterogeneity of the primary chemical structures is reflected in the self-assembled supramolecular structures. In the bulk state, the full phase diagram is identified as BCC $\to $ HEX $\to $ LAM $\to $ DG $\to $ inversed HEX at sub-10 nm length scale when the volume fraction of POSS increase in linear PSm-(POSS)n. The phase structures can also be affected by tuning the topology and functionality at the same volume fraction. In the solution state, as the number of POSS or connection branches increase, the small packing parameters with structures evolve from vesicles $\to $ long cylinders $\to $ short cylinders $\to $ spheres. [Preview Abstract] |
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M1.00020: Tuning Structural Properties of Biocompatible Block Copolymer Micelles by Varying Solvent Composition Tyler Cooksey, Avantika Singh, Kim Mai Le, Shu Wang, Elizabeth Kelley, Lilin He, Sameer Vajjala Kesava, Enrique Gomez, Bryce Kidd, Louis Madsen, Megan Robertson The self-assembly of block copolymers into micelles when introduced to selective solvents enables a wide array of applications, ranging from drug delivery to personal care products to nanoreactors. In order to probe the assembly and dynamics of micellar systems, the structural properties and solvent uptake of biocompatible poly(ethylene oxide-b-$\varepsilon $-caprolactone) (PEO-PCL) diblock copolymers in deuterated water (D$_{\mathrm{2}}$O) / tetrahydrofuran (THF$_{\mathrm{d8}})$ mixtures were investigated using small-angle neutron scattering in combination with nuclear magnetic resonance. PEO-PCL block copolymers, of varying molecular weight yet constant block ratio, formed spherical micelles through a wide range of solvent compositions. Varying the composition from 10 to 60 {\%} by volume THF$_{\mathrm{d8\thinspace }}$in D$_{\mathrm{2}}$O / THF$_{\mathrm{d8}}$ mixtures was a means of varying the core-corona interfacial tension in the micelle system. An increase in THF$_{\mathrm{d8}}$ content in the bulk solvent increased the solvent uptake within the micelle core, which was comparable for the two series, irrespective of the polymer molecular weight. Differences in the behaviors of the micelle size parameters as the solvent composition varied originated from the differing trends in aggregation number for the two micelle series. Incorporation of the known unimer content determined from NMR allowed refinement of extracted micelle parameters. [Preview Abstract] |
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M1.00021: Visualization of Topology through Simulation Andrew Mulderig, Gregory Beaucage, Karsten Vogtt, Hanqiu Jiang Complex structures can be decomposed into their minimal topological description coupled with complications of tortuosity. We have found that a stick figure representation can account for the topological content of any structure and coupling with scaling measures of tortuosity we can reconstruct an object. This deconstruction is native to static small-angle scattering measurements where we can obtain quantitative measures of the tortuous structure and the minimal topological structure. For example, a crumpled sheet of paper is composed of a minimal sheet structure and parameters reflecting the extent of crumpling. This quantification yields information that can be used to calculate the hydrodynamic radius, radius of gyration, structural conductive pathway, modulus, and other properties of complex structures. The approach is general and has been applied to a wide range of nanostructures from crumpled graphene to branched polymers and unfolded proteins and RNA. In this poster we will demonstrate how simple structural simulations can be used to reconstruct from these parameters a 3d representation of the complex structure through a heuristic approach. Several examples will be given from nano-fractal aggregates. [Preview Abstract] |
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M1.00022: The effect of molecular architecture on segmental and chain dynamics in poly(styrene$_{\mathrm{n}}$-isoprene$_{\mathrm{n}})$ miktoarm block copolymers Thomas Kinsey, Joshua Sangoro, Weiyu Wang Poly(styrene$_{\mathrm{n}}$-isoprene$_{\mathrm{n}})$ miktoarm block copolymers have been investigated by broadband dielectric spectroscopy to determine the effect of molecular architecture on chain and segmental dynamics. In contrast to linear PS-$b$-PI systems of the same morphology, a slow PI chain relaxation emerges for the miktoarm systems. This additional dielectric process is attributed to differences in the molecular architecture. The results are discussed within the framework of Milner theory and recent models of polymer dynamics. [Preview Abstract] |
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M1.00023: Photo-processing P3HT conjugated polymers, in solution: A new route towards ordered polymeric structures. Newton Barbosa Neto, Marcia Dutra, Paulo Araujo, Renato Sampaio Solution aggregated thin films of conjugated polymers have demonstrated to be promising materials for many applications, e.g., solar cells and field-effect transistors. There are many standard methods to generate aggregates in polymeric solution, which includes poor solvent addiction and solution temperature manipulation. Here, we demonstrate a new approach to induce aggregate formation on solution of P3HT polymer. Under light excitation with 355 nm or 532 nm pulsed laser the polymer exhibit significant changes on its UV-Vis spectrum which are most known in the literature as the formation of H-J aggregates and additional new bands associated with polaron formation. Such changes in the amorphous phase of the polymers are seen in specific conditions of solvent combinations. We show also the dependency on the excitation laser power which can be identified as a threshold to ignite the formation of the new structure. We are grateful to CNPq and CAPES for financial support. [Preview Abstract] |
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M1.00024: Binders for Energetics - Modelling and Synthesis in Harmony Licia Dossi, Doug Cleaver, Peter Gould, Jim Dunnett, Hamish Cavaye, Laurence Ellison, Federico Luppi, Ron Hollands, Mark Bradley The \textit{Binders by Design} UK programme develop new polymeric materials for energetic applications that can overcome problems related to chemico-physical properties, aging, additives, environmental and performance of energetic compositions. Combined multi-scale modelling and experiment is used for the development of a new modelling tool and with the aim to produce novel materials with great confidence and fast turnaround. New synthesised binders with attractive properties for energetic applications used to provide a high level of confidence in the results of developed models. Molecular dynamics simulations investigate the thermal behaviour and the results directly feed into a Group Interaction Model (GIM). A viscoelastic constitutive model has been developed examining stress development in energetic/binder configurations. GIM data has been used as the basis for developing hydrocode equations of state, which then applied in run-to-detonation type investigations to examine the effect of the shock properties of a binder on the reactivity of a typical Polymer Bonded Explosive in a high-velocity impact type scenario. The \textit{Binders by Design} UK programme is funded through the Weapons Science and Technology Centre by DSTL. [Preview Abstract] |
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M1.00025: Nanostructures of Weakly Fluorinated Bottlebrush Polymers in Thin Films Dongsook Chang, Matthew Burch, Jan-Michael Carrillo, Yingdong Luo, Alex Belianinov, Kunlun Hong, Olga Ovchinnikova, Bobby Sumpter The surface and internal nanostructures of weakly fluorinated bottlebrush polymers are studied in detail. Annealed films demonstrate the formation of holes on the surface, presumably due to a mismatch between the film thickness and the bottlebrush size. The formation of holes is analyzed with varied film thickness, backbone length, and annealing condition. The internal nanostructures of bottlebrush films are characterized using microscopy techniques in conjunction with plasma etching. [Preview Abstract] |
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M1.00026: Orthogonal Self-Assembly of Block Copolymer Thin Films on Minimal Topographic Patterns Jaewon Choi, Yinyong Li, Feng Liu, Kenneth Carter, Thomas Russell We have studied the orthogonal self-assembly behavior of cylinder-forming block copolymers (BCPs) on minimal topographic patterns. When BCP film thickness was comparable to the natural period of BCP ($L_{0})$, it was found that cylindrical microdomains oriented parallel to the film surface were randomly oriented on the minimal topographic pattern with the confinement depth of 0.71$L_{0}$. With increasing the film thickness, these microdomains became more aligned orthogonal to the direction of the underlying minimal topographic pattern, eventually generating orthogonally aligned line patterns at the film thickness of 1.70$L_{0}$. We also found that the confinement depth of the minimal topographic pattern was an important factor to induce orthogonal self-assembly of BCP thin films. The lateral ordering of orthogonally aligned line patterns were characterized using grazing incidence small angle X-ray scattering (GISAXS), where an orientation parameter was found to be 0.997. [Preview Abstract] |
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M1.00027: Effects of solvent evaporation conditions on solvent vapor annealed cylinder-forming block polymer thin films Meagan Grant, William Jakubowski, Gunnar Nelson, Chloe Drapes, A Baruth Solvent vapor annealing is a less time and energy intensive method compared to thermal annealing, to direct the self-assembly of block polymer thin films. Periodic nanostructures have applications in ultrafiltration, magnetic arrays, or other structures with nanometer dimensions, driving its continued interest. Our goal is to create thin films with hexagonally packed, perpendicular aligned cylinders of poly(lactide) in a poly(styrene) matrix that span the thickness of the film with low anneal times and low defect densities, all with high reproducibility, where the latter is paramount. Through the use of our computer-controlled, pneumatically-actuated, purpose-built solvent vapor annealing chamber, we have the ability to monitor and control vapor pressure, solvent concentration within the film, and solvent evaporation rate with unprecedented precision and reliability. Focusing on evaporation, we report on two previously unexplored areas, chamber pressure during solvent evaporation and the flow rate of purging gas aiding the evaporation.~We will report our exhaustive results following atomic force microscopy analysis of films exposed to a wide range of pressures and flow rates. Reliably achieving well-ordered films, while occurring within a large section of this parameter space, was correlated with high-flow evaporation rates and low chamber pressures. These results~have significant implications on other methods of solvent annealing, including ``jar'' techniques. [Preview Abstract] |
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M1.00028: Nanoscale Substrate Roughness for the Tailored Control of Block Copolymer Thin film Orientation Justin Cheung, Mani Sen, Maya Endoh, Tadanori Koga Directed self-assembly of block copolymers (BCP) in thin films is crucial to many technologies. Of interest is the ability to engineer the orientation of BCP cylinder formation on solid substrates. Here we report the capacity of a homopolymer ``substrate'' with tailored nanoscale surface roughness to control BCP cylinder orientation. Poly-2-vinylpyridine (P2VP) nanometer-thick adsorbed polymer layers (``adsorbed nanolayers'') were prepared on cleaned Si substrates using a solvent leaching process [1]. Additionally, it was demonstrated that the length of annealing time allowed for control over surface roughness of the P2VP adsorbed nanolayers [1]. Polystyrene-\textit{block}-poly (4-vinylpyridine) (PS-$b$-P4VP) was then spin cast atop the P2VP adsorbed nanolayer and thermally annealed. A suite of experimental techniques evidenced the formation of perpendicularly oriented cylinders in PS-b-P4VP thin films (30-120 nm in thickness) on the underlying roughened P2VP surface, while the parallel orientation was favored on a smooth Si surface coated with a native oxide layer. Details will be discussed in the presentation. [1] N. Jiang et al., Macromolecules, 47, 2014, 2682 [Preview Abstract] |
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M1.00029: Lamellae to Gyroid Epitaxial Transitions in Weakly Segregated Diblock Copolymers Feng Qiu, Nan Ji, Ping Tang, An-Chang Shi We combine the string method and self-consistent field theory (SCFT) for polymers to investigate the kinetic pathways connecting the lamella (L) and gyroid (G) phases in weakly segregated block copolymers. We focus on the nucleation and growth mechanism as well as the spinodal decomposition, in which a nucleus of the new phase grows locally, or the old phase evolves gradually to the new phase, respectively. Through this method, the free energy landscape for the transition from L to G can be obtained and the epitaxial relationship and several metastable states between L and G phases are systematically studied. In particular, the one-step mechanism and two-step mechanism are distinguished. The details of the nucleation and growth of the Perforated Lamella (PL) structure and G phase are presented. Our result is helpful in understanding the kinetic relationship among L, G, and PL phases in microphase transitions of diblock copolymers. [Preview Abstract] |
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M1.00030: Molecular dynamics study on microstructures of diblock copolymer melts with soft potential and potential recovery Seulwoo Kim, Ji Ho Ryu, Han Sol Wee, Won Bo Lee The method for obtaining various self-assembled microstructures with block copolymers, was investigated using molecular dynamics (MD) simulation. However, it requires expensive computational cost time to prepare initial configurations of various self-assembled structures because of topological constraints. Furthermore, manual preparation often becomes a complicated and time-consuming procedure even for the simplest structures, a lamellar phase, not to mention more complicate phases, such as a gyroid phase. The difficulty may be overcome by introducing a soft potential, which allows the system to reach a self-assembled state quickly (within 3$\tau_d$). Once a self-assembled microstructure is obtained, the normal potential, for instance, Weeks-Chandler-Andersen (WCA) potential, is restored and equilibration runs are performed to calculate various properties of the microstructures. With our approach, various equilibrated phase structures—including S (spherical), H (hexagonal), G (gyroid), and L (lamellar) phases—are obtained. To verify our method, static and dynamic properties of the lamellar phase are examined with previous results. [Preview Abstract] |
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M1.00031: Understanding ordering of block-copolymer-based supramolecules on lithographically patterned surfaces Katherine Evans, Ting Xu Block copolymer-based supramolecular self-assembly offers a simple method to overcome issues with incommensurability, surface chemistry, and assembly kinetics to access a range of nanostructures. However, for many applications, precise control over the location, directionality, and spacing of supramolecular features is necessary. Here, the stoichiometry of the small molecule that comprises one component of the supramolecule and the solvent annealing condition were systematically investigated to achieve control over the ordering of thin films on flat and templated substrates. It was shown that manipulating these two parameters can create long-range, directional ordering of the supramolecule in the templated surface with a low defect-density. Upon ordering, the periodicity of the templated pattern changes, but one uniform periodicity can be achieved by changing the film thickness. [Preview Abstract] |
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M1.00032: Morphologies of miktoarm polymer in thin film Hyeyoung Kim, Beom-goo Kang, Sergey Chernyy, Matthias Arras, Zhiwei Sun, Jaewon Choi, Gregory Smith, Thomas Russell The morphologies of A2B and ABC mikto-arm polymer in thin film were examined. The asymmetry of chain architecture of A2B mikto-arm polymer affects to the morphologies in thin film state. The change in the morphology under solvent vapor annealing for different ratio of solvent and different periods of time was observed by AFM. By comparing corresponding di-block copolymer, we proved that the phase diagram is shifted to higher volume fractions of the one block because of its asymmetric conformation. We also observed the long-range ordering formed on the saw-tooth pattern. The morphologies of ABC mikto-arm terpolymer consisted of polystyrene, polyisoprene and poly(2-vinyl pyridine) (PS-PI-P2VP) were examined by SAXS, AFM and TEM. We studied the structures for different annealing temperatures. The various types of self-assembly structures were observed because the interaction energy between each arms are changed depending on the temperature. [Preview Abstract] |
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M1.00033: Trivalent anions in polymerized ionic liquids enhance both ion conductivity and viscosity Joshua Bartels, Matthew Helgeson, Rachel Segalman The conductive and mechanical properties of polymerized ionic liquids (PILs) are strongly affected by the pendant ion and counter-ion. By including a mixture of two counter-ions, each ion may uniquely interact with the PIL and each give rise to a separate property. By including both a conductive ion (chloride) and a coordinating ion (phosphate) into a PIL, the mechanical and conductive properties may be decoupled. The incorporation of trivalent ions to an imidazolium-containing PIL results in stronger inter-polymer associations observed in rheological measurements as an increase in the polymer viscosity with increasing phosphate content. Phosphate ions bind more strongly with imidazoliums and allow chloride ions to more readily conduct. The ionic conductivity was determined by AC impedance and was found to increase with increasing phosphate content. At sufficiently high phosphate concentrations, the conductivity of the PIL with trivalent ions is superior to that of the neat PIL. The effect of incorporating trivalent anions is nontrivial as it also affects the organization and aggregation of ions, observed as a shift in the ion correlation peak observed in small angle x-ray scattering to shorter correlation distances. [Preview Abstract] |
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M1.00034: Elucidating the correlation between morphology and ion dynamics in polymerized ionic liquids. Maximilian Heres, Tyler Cosby, Ciprian Iacob, James Runt, Roberto Benson, Hongjun Liu, Stephen Paddison, Joshua Sangoro Charge transport and dynamics are investigated for a series of poly-ammonium and poly-imidazolium-based polymerized ionic liquids (polyIL) with a common bis(trifluoromethylsulfonyl)imide anion using broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry. A significant enhancement of the Tg independent ionic conductivity is observed for ammonium based polyIL with shorter pendant groups, in comparison to imidazolium based systems. These results emphasize the importance of polymer backbone spacing as well as counter-ion size on ionic conductivity in polymerized ionic liquids. [Preview Abstract] |
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M1.00035: Electrode polarization and ion dynamics at the metal-ionic liquid interface Zachariah Vicars, Tyler Cosby, Joshua Sangoro Charge transport at the metal-ionic liquid interface is investigated by broadband dielectric spectroscopy. The dielectric spectra at low frequencies are dominated by electrode polarization, a phenomenon that is shown to depend on the geometry of the sample, transport properties of the ionic liquids and material of the metal electrodes. An analytical model of electrode polarization accounting for these factors will be discussed. [Preview Abstract] |
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M1.00036: Charge Transport and Dynamics of Ionic Liquids: Evaluating the Impact of Mesoscale Organization Tyler Cosby, Zachariah Vicars, Joshua Sangoro Charge transport and dynamics in a homologous series of imidazolium-based ionic liquids are investigated by broadband dielectric spectroscopy to elucidate the impact of alkyl chain length and hydrophobic aggregation on their physicochemical properties. It is observed that systematic ordering of ionic liquids into complex polar and nonpolar domains results in the emergence of a slow dielectric relaxation as well as a decrease in the ionic conductivity. The results are discussed within the framework of current understanding of charge transport and dynamics in ionic liquids. [Preview Abstract] |
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M1.00037: Ion transport in precisely controlled phosphonated polymers Sanghee Jang, Moon Jeong Park There is a great demand for the development of new polymer electrolytes that show enhanced ion conductivity under high temperature and low humidity conditions. In this regard, polymers carrying phosphonic acid groups have been attracting attention owing to several beneficial features of phosphonic acid, i.e., high degree of self-dissociation and amphoteric characteristics. This can lead to effective hydrogen bonding interactions and thereby facilitate fast proton transport under dry conditions. In this study, we synthesize a series of phosphonated polymers with controlled phosphonic acid concentration. In particular, by precisely controlling the position of phosphonic acid groups, we show the modulation of proton transport properties at the same ion contents. Morphology analysis of the synthesized polymers has also been performed by combining small-angle and wide-angle X-ray scattering experiments.. [Preview Abstract] |
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M1.00038: Morphology and conductivity of PEO-based polymers having various end functional groups Ha Young Jung, Prithwiraj Mandal, Moon Jeong Park Poly(ethylene oxide) (PEO)-based polymers have been considered most promising candidates of polymer electrolytes for lithium batteries owing to the high ionic conductivity of PEO/lithium salt complexes. This positive aspect prompted researchers to investigate PEO-containing block copolymers prepared by linking mechanically robust block to PEO covalently. Given that the microphase separation of block copolymers can affect both mechanical properties and ion transport properties, various strategies have been reported to tune the morphology of PEO-containing block copolymers. In the present study, we describe a simple means for modulating the morphologies of PEO-based block copolymers with an aim to improve ion transport properties. By varying terminal groups of PEO in block copolymers, the disordered morphology can be readily transformed into ordered lamellae or gyroid phases, depending on the type and number density of end group. In particular, the existence of terminal groups resulted in a large reduction in crystallinity of PEO chains and thereby increasing room temperature ionic conductivity. [Preview Abstract] |
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M1.00039: The effect of varying molecular weight on ion-transport properties in polymeric ionic liquids Jordan Keith, Faisal Aldukhi, Santosh Mogurampelly, Bill Wheatle, Venkat Ganesan We performed atomistic molecular dynamics simulations on polymerized 1-butyl-3-vinylimidazolium ionic liquid with a $PF_6^-$ counterions to study the influence of the molecular weight of the polymer on the ion mobilities and mechanisms underlying ion transport. As the molecular weight of the polymer increases, the diffusivity of the counterions decreases, but plateaus around a polymer length of 7-12 monomer units. We rationalize this result by invoking the molecular weight dependence of ion-pair dynamics, ion hopping mechanisms, polymer segmental motion, orientational relaxation, and coordination statistics. [Preview Abstract] |
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M1.00040: Multivalent Ion Transport Through Polymerized Ionic Liquids Nicole Michenfelder-Schauser, Gabriel Sanoja, Rachel Segalman Fundamental studies of multivalent ion transport through polymers have been limited due to a lack of polymer systems that can dissolve multivalent salts but still allow for appreciable ion motion upon application of an electric field. Multivalent ion transport in polymers is made possible by exploiting kinetically labile metal-ligand coordination in a polymerized ionic liquid (PIL). A poly(ethylene oxide)-based polymer with pendant imidazole groups is mixed with various metal-bis(trifluoromethanesulfonyl)imide salts to form PILs with low glass transition temperatures. The ion transport characteristics of each PIL are characterized via AC impedance spectroscopy and show comparable conductivities for monovalent, divalent and trivalent ions roughly 1.5 orders of magnitude higher than the neat polymer. We use molecular characterization techniques to quantify kinetic rate parameters that have an impact on conductivity. We determined simple scaling relationships, beyond solely correcting for segmental chain motion, that create a unified description of transport mechanism for multivalent ion transport through polymeric systems. [Preview Abstract] |
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M1.00041: Liquid crystalline polymer electrolyte membranes with ion gating properties Jinwei Cao, Camilo Piedrahita, Kagami Koterasawa, Abegel Freedman, Juliana Martins, Thein Kyu, Coleen Pugh, Kaoru Adachi, Yasuhisa Tsukahara Polymer electrolyte membranes (PEMs) with ion conducting channels have been fabricated via photo-polymerization of liquid crystalline monomers, synthesized in our laboratory. The monomers consist of polyethylene glycol segments as the ion conduction medium and photoactive azobenzene mesogen. Guided by the phase diagram of azobenzene LC and nematic LC, ion conducting channels are formed in the liquid crystalline phases. Ionic conductivities of the azobenzene LCs were measured in trans-state and cis-state using AC impedance spectroscopy. By applying UV or visible light, the opening/closing of ion channels may be controlled through rapid trans-cis isomerization of azobenzene mesogen by light irradiation. Therefore, the ion conduction ability of the PEMs can be optically controlled, affording ion gating capability of the PEMs. These PEMs can act as the ion conducting channels on cell membranes and, therefore, may be used to construct artificial neurons. Supported by NSF-DMR 1502543 [Preview Abstract] |
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M1.00042: Molecular Weight Dependence of the Intrinsic Size Effect on $T_{\mathrm{g}}$ in AAO Template-Supported Polymer Nanorods: A DSC Study Tong Wei, Shadid Askar, Anthony Tan, John Torkelson We have investigated how the intrinsic size effect modifies the glass transition temperature ($T_{\mathrm{g}})$ and fragility of template-supported polystyrene (PS) nanorods in the absence of free surfaces and attractive polymer-substrate interactions. Template-supported nanorods of different molecular weight (MW) were prepared by melt infiltration; rod diameter ($d)$ varied from 24 nm to 210 nm. The $T_{\mathrm{g}}$- and fragility-confinement effects$_{\mathrm{\thinspace }}$were characterized using differential scanning calorimetry. $T_{\mathrm{g}}$-confinement effects are observed for PS nanorods MW $\ge $ 900 kg/mol; greater perturbations to~$T_{\mathrm{g}}$~are observed with increasing MW ($e.g.$, in 24 nm rods,~$T_{\mathrm{g,rod}}$~--~$T_{\mathrm{g,bulk}}$~$=$ -3.2 $^{\circ}$ C for 900 kg/mol PS, whereas~$T_{\mathrm{g,rod}}$~--~$T_{\mathrm{g,bulk}}$~$=$ -7.4 $^{\circ}$ C for 3,840 kg/mol PS). Intrinsic size effects can account for the MW-dependent behavior in PS nanorods. Comparing the length scale of the confining dimension, $d$, to that of the polymer radius of gyration,~$R_{\mathrm{g}}$. Perturbations to~$T_{\mathrm{g}}$~were observed when $d$ \textless 2$R_{\mathrm{g}}$. This result indicates that changes in polymer chain conformations due to confinement is important in perturbing~$T_{\mathrm{g}}$~in template-supported PS nanorods. We also determined that the $T_{\mathrm{g}}$-confinement is accompanied by a fragility-confinement effect. The fragility of 33-nm-diameter, 2,000 kg/mol PS nanorods is reduced 24{\%} from the bulk value. \quad [Preview Abstract] |
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M1.00043: Equilibrium Polymerization of Butyl Methacrylate in Bulk and in Nanopore Confinement Qian Tian, Sindee Simon The equilibrium between monomer and polymer in free radical polymerization can be shifted towards monomer under nanoconfinement. This decrease in ceiling temperature is due to a decrease in the entropy associated with the constrained polymer chains, resulting in a larger negative change in entropy of reaction. Here, we investigate the equilibrium polymerization of butyl methacrylate (BMA) in bulk and in nanopore confinement with differential scanning calorimetry (DSC) using di-tert-butyl peroxide (DTBP) as initiator. This system has several advantages compare to the previously studied system of methyl methacrylate (MMA) initiated with 2,2'-azo-bis-isobutyronitrile (AIBN), namely, a reduced rate of reaction, higher boiling point of monomer, and higher initiator utilization temperature range, all of which facilitate the study of the reaction at high temperatures near the ceiling temperature. Interestingly, for BMA, there is no change in limiting conversion between material reacted in bulk and that in controlled pore glass having pore diameters of 7.5 and 50 nm. This unexpected result may be due to the greater flexibility of the PBMA chains compared to PMMA, suggesting that in the BMA/PBMA system, the degree of confinement is relatively low. Future studies will continue to investigate how the entropy change on reaction is affected by confinement. [Preview Abstract] |
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M1.00044: The effect of polymer architecture on the interdiffusion in thin polymer films. Ayse Caglayan, Guangcui Yuan, Sushil K. Satija, David Uhrig, Kunlun Hong, Bulent Akgun Branched polymer chains have been traditionally used in industrial applications as additives. Recently they have found applications in electrochromic displays, lithography, biomedical coatings and targeting multidrug resistant bacteria. In some of these applications where they are confined in thin layers, it is important to understand the relation between the mobility and polymer chain architecture to optimize the processing conditions. Earlier interdiffusion measurements on linear and cyclic polymer chains demonstrated the key role of chain architecture on mobility. We have determined the vertical diffusion coefficients of the star polystyrene chains in thin films as a function of number of polymer arms, molecular weight per arm, and film thickness using neutron reflectivity (NR) and compare our results with linear chains of identical total molecular weight. Bilayer samples of 4-arm and 8-arm protonated polystyrenes (hPS) and deuterated polystyrenes (dPS) were used to elucidate the effect of polymer chain architecture on polymer diffusion. NR measurements indicate that the mobility of polymer chains in thin films get faster as the number of polymer arms increases and the arm molecular weight decreases. Both star polymers showed faster interdiffusion compared to their linear analog. Diffusion coefficient of branched PS chains has a weak dependence on the film thickness. [Preview Abstract] |
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M1.00045: Exploring ultrastability in nanostructured glassy polymer films by fast-scanning calorimetry. Mithun Chowdhury, Yucheng Wang, Hyuncheol Jeong, Daniele Cangialosi, Rodney Priestley A decade ago ultra-stable small molecule glass formers were discovered. Since then a significant amount of research has been devoted to traverse down the energy landscape of such glass formers via physical vapor deposition (PVD). Matrix assisted pulsed laser evaporation (MAPLE) has the known ability to produce vapour deposited nanostructured polymer glass with exceptional kinetic stability. We explored the role of deposition temperature/ growth rate on thermodynamic and kinetic stabilities of poly (methyl methacrylate) (PMMA) films, deposited over a fast-scanning calorimetry sensor. We found in general any MAPLE deposited glass is kinetically more stable than bulk polymer and its spin-coated film. Moreover slow growth rate and optimum temperature during MAPLE deposition can additionally lead to thermodynamically stable (low-energy) glass. The role of interfaces formed through dramatic nanostructuring and packing of nanoglobules (removal of void space) may have additional role on such ultrastability. [Preview Abstract] |
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M1.00046: Flory-Stockmayer analysis on reprocessable polymer networks Lingqiao Li, Xi Chen, Kailong Jin, John Torkelson Reprocessable polymer networks can undergo structure rearrangement through dynamic chemistries under proper conditions, making them a promising candidate for recyclable crosslinked materials, e.g. tires. This research field has been focusing on various chemistries. However, there has been lacking of an essential physical theory explaining the relationship between abundancy of dynamic linkages and reprocessability. Based on the classical Flory-Stockmayer analysis on network gelation, we developed a similar analysis on reprocessable polymer networks to quantitatively predict the critical condition for reprocessability. Our theory indicates that it is unnecessary for all bonds to be dynamic to make the resulting network reprocessable. As long as there is no percolated permanent network in the system, the material can fully rearrange. To experimentally validate our theory, we used a thiol-epoxy network model system with various dynamic linkage compositions. The stress relaxation behavior of resulting materials supports our theoretical prediction: only 50 \% of linkages between crosslinks need to be dynamic for a tri-arm network to be reprocessable. Therefore, this analysis provides the first fundamental theoretical platform for designing and evaluating reprocessable polymer networks. [Preview Abstract] |
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M1.00047: The Effect of Plant Source on the Structural Properties of Lignin-based Polyurethane Blends Jason Lang, Mark Dadmun The development of polyurethane materials based on incorporating lignin from a variety of plant sources (softwood, hardwood, and non-wood) were synthesized. Further experiments study the physical properties of the resulting lignin-based polyurethane as a function of the lignin structure, which varies with plant source. Here, we report the effect that internal crosslinking of the lignin structure has on the modulus, hardness, glass transition temperature, and thermal decomposition of the synthesized lignin-based polyurethane composites. The lignins used in this work were a softwood kraft lignin, hardwood lignosulfonate, and a wheat straw soda lignin. The lignin, acting as a polyol and the hardblock segment, reacts with TDI-endcapped PPG (2,300 M$_{N})$ as the rubbery softblock component to produce lignin-based polyurethanes with varying lignin content (10, 20, 30, 40, 50, and 60 wt{\%}). Results show that the wheat straw lignin provides the superior mechanical properties and thermal resistance. These properties are correlated to the two-phase morphology of the resultant polyurethane. [Preview Abstract] |
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M1.00048: Preparation Details for Making Silicones: Influence of Molecular Network Architecture on Mechanical and Surface Properties of PDMS Elastomers Matthew Melillo, Edwin Walker, Zoe Klein, Kirill Efimenko, Jan Genzer Poly(dimethylsiloxane) (PDMS) is one of the most common elastomers, with applications ranging from medical devices to absorbents for water treatment. Fundamental understanding of how liquids spread on the surface of and absorb into PDMS networks is of critical importance for the design and use of another application - microfluidic devices. We have systematically studied the effects of polymer molecular weight, loading of tetra-functional crosslinker, end-group chemical functionality, the extent of dilution of the curing mixture, and gelation kinetics on the mechanical and surface properties of end-linked PDMS networks. The gel and sol fractions, storage and loss moduli, liquid swelling ratios, and water contact angles have all been shown to vary greatly based on the aforementioned variables. Similar trends were observed for the commercial PDMS material, Sylgard-184. Our results have confirmed theories predicting the relationships between modulus and swelling and we've also applied the theory of Macosko-Miller to estimate extent of reaction of crosslinker and polymer groups. Methods for determining the molecular weight between crosslinks from swelling, mechanical, and gelation theories were applied to ascertain their similarities and differences in an effort to identify the most accurate method. These findings will aid in the design and implementation of efficient microfluidics and other PDMS-based materials that involve the transport of liquids. [Preview Abstract] |
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M1.00049: Structural Characterization of supramolecule/nanoparticle nanocomposites Yihan Xiao, Ting Xu Supramolecular nanocomposites offer great opportunities toward functional materials. However, these systems also challenge our basic understanding in self-assembly in multiple component systems. The multicomponent nature of the supramolecular system introduces significant complexity in mapping out the hierarchical spatial distribution of each building block. To this end, various techniques have been adopted to decouple the convoluted structures. Transmission electron microscopy (TEM), scanning transmission electron microscopy tomography (STEMT) and small-angle X-ray scattering (SAXS) collaboratively determined the hexagonal structure of nanoparticle superlattice. Resonant X-ray scattering (RSoXS) provides a novel opportunity to selectively characterize the lamellar arrangement of supramolecular matrix. Finally, a model is proposed for the nanocomposite morphology based on these results that is critical toward delineation of energetic contribution from individual component. [Preview Abstract] |
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M1.00050: Self-assembled nanocages based on the coiled coil bundle motif Nairiti Sinha, Jose Villegas, Jeffery Saven, Kristi Kiick, Darrin Pochan Computational design of coiled coil peptide bundles that undergo solution phase self-assembly presents a diverse toolbox for engineering new materials with tunable and pre-determined nanostructures that can have various end applications such as in drug delivery, biomineralization and electronics. Self-assembled cages are especially advantageous as the cage geometry provides three distinct functional sites: the interior, the exterior and the solvent-cage interface. In this poster, syntheses and characterization of a peptide cage based on computationally designed homotetrameric coiled coil bundles as building blocks is discussed. Techniques such as Transmission Electron Microscopy (TEM), Small-Angle Neutron Scattering (SANS) and Analytical Ultracentrifugation (AUC) are employed to characterize the size, shape and molecular weight of the self-assembled peptide cages under different pH and temperature conditions. Various self-assembly pathways such as dialysis and thermal quenching are shown to have a significant impact on the final structure of these peptides in solution. Comparison of results with the target cage design can be used to iteratively improve the peptide design and provide greater understanding of its interactions and folding. [Preview Abstract] |
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M1.00051: Effects of wet-dry cycling on structure and performance of sulfonated pentablock copolymer membranes. Phuc Truong, Gila Stein, Haleh Ardebili, Mejdi Kammoun Membranes based on sulfonated block copolymers have shown potential for water purification, but the structure and performance of these materials have not been studied after soaking in water and drying in air. In this work, we investigate the structure, mechanics, and transport properties of solution-cast sulfonated pentablock copolymer membranes as a function of wet-dry cycling, where one cycle is defined as a 24 hour soak in de-ionized water followed by a 24 hour drying period at 50{\%} RH. The as-prepared membrane is comprised of disordered micellar domains with sulfonated styrene cores and ethylene-propylene/t-butyl styrene coronas. This initial state can be stretched under tension to 50{\%} elongation, absorbs up to 20 wt{\%} water at 55{\%} RH, exhibits proton conductivity of 0.003 mS/cm, and water vapor transport rates of 0.5 kg/m$^{2}$/day. After the first cycle, the sulfonated domains are merged into a near-continuous network, and the membranes exhibit enhanced modulus, stress at break and yield stress. With further cycling, the domains continue merging into a continuous network, and transport properties are unchanged. However, at cycle 6, the water uptake declines to 6 wt{\%}, and the films become very brittle with only 5{\%} elongation. [Preview Abstract] |
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M1.00052: Molecular Simulation Evaluation of Macromolecular Transport through Nanofiltration Membranes Noelia Almodovar Arbelo, Bryan Boudouris, David Corti A hybrid Monte Carlo and Molecular Dynamics simulation technique was implemented to elucidate the equilibrium behavior and transport properties of a model macromolecule as it navigated across a nanoporous polymer thin film (i.e., a nanofiltration membrane). The model linear homopolymer chosen was one that had interactions that were representative of poly(ethylene oxide) (PEO) due to the known interactions of PEO with solution molecules when a PEO chain is dissolved in an aqueous environment. The structural rearrangements of the PEO chain as it passes through the nanopore under an imposed chemical potential gradient was quantified as a function of solvent quality, polymer chain length, nanopore diameter and shape, and PEO-nanopore wall interactions. Thus, these computational studies provide a more detailed picture of the underlying physical mechanisms that drive macromolecular transport through nanopores, and, in particular, how dimensionally-large macromolecules (i.e., with large radii of gyration) enter and move through dimensionally-small pores (i.e., small radii nanopores). The insights gained from these studies will aid in the development of more cost-effective water purification systems in separation technologies for myriad industrial applications. [Preview Abstract] |
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M1.00053: NIST's Polarized Resonant Soft X-ray Scattering facility to measure chemical structure and molecular orientation on the nano-scale Eliot Gann, Daniel Fischer, Dean Delongchamp NIST is developing a new Polarized Resonant Soft X-ray Scattering (P-RSoXS) facility at the NSLS-II synchrotron located in Brookhaven National Laboratory. This facility will enable the highest quality ensemble measurements of the nanoscale distribution of molecular species and orientations in both high-throughput ex-situ measurements and diverse specialized in-situ experiments. The facility's current state of design will be presented, along with a survey of applications in fields from thin-film organic electronics, and biology to energy and environmental sciences. A dialog with the community regarding potential applications is encouraged. [Preview Abstract] |
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M1.00054: Manipulating Energy Transfer in Conjugated Polymers using Radical Mediators Daniel Wilcox, Sanjoy Mukherjee, Bryan Boudouris Previous efforts have demonstrated that polymers containing open-shell moieties can be used to improve the performance of organic electronic devices (e.g., organic field-effect transistors (OFETs) and photovoltaic devices). However, the exact mechanism of how these redox-active radical polymers improve the performance of these next-generation devices has yet to be described in full. Here, we take the first steps towards elucidating this full picture by demonstrating that the galvinoxyl radical can be used as an electron acceptor for a common electron-donating macromolecule. First, galvinoxyl was used as a fluorescence quencher for poly(3-hexylthiophene) (P3HT) with quenching performance on par with that of oft-used fullerene derivatives. This effect was caused by photoinduced electron transfer between the two materials. Additionally, the galvinoxyl radical was used as an active layer dopant for P3HT OFETs. By increasing the P3HT carrier density through spontaneous electron transfer, the behavior of the device was changed from that of an intrinsic semiconductor to that of a highly-doped semiconductor. Thus, these initial studies lay the foundation for a paradigm where open-shell entities are used to dope conjugated polymer semiconductors for high-performance device applications. [Preview Abstract] |
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M1.00055: Renewable chiral nematic liquid crystal template for highly ordered semiconducting polymers Bailey Risteen, Alyssa Blake, Michael McBride, Cornelia Rosu, Jung Ok Park, Mohan Srinivasarao, Paul Russo, Elsa Reichmanis The future of organic electronics relies on the ability to facilitate intra- and interchain ordering of semiconducting polymers (SPs). In this work, cellulose nanocrystals (CNCs), a material derived from biomass, was used to enhance the alignment of semiconducting polymer poly[3-(potassium-4-butanoate) thiophene-2,5-diyl] or PPBT through liquid crystal ordering. CNCs are rod-like particles that form a chiral nematic liquid crystal phase. The inclusion of these renewable particles in PPBT solutions resulted in highly birefringent domains under polarized optical microscopy, demonstrating the ability of CNCs to ``template'' PPBT into liquid crystal phases. The presence of PPBT $\pi $-$\pi $ stacks was confirmed by both a bathochromic shift as well as the position and intensity of 0-0 and 0-1 vibrational peaks in UV-Vis spectroscopy. Circular dichroism (CD) spectroscopy showed that the PPBT/CNC blends were chiral and had a pronounced negative CD peak at the $\pi $-$\pi $ stacking wavelength (578 nm), providing evidence that these stacking interactions had a helicoidal twist. [Preview Abstract] |
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M1.00056: Index matching of TE and TM modes in organic multilayer waveguides Jonathan Thompson, Heidrun Schmitzer, Hans Peter Wagner We investigate transverse electric (TE) and magnetic (TM) mode propagation in organic multilayers consisting of aluminum quinoline (Alq$_{\mathrm{3}})$ and perylenetetracarboxylic dianhydride (PTCDA). In particular, we analyze two multilayer waveguides, Alq$_{\mathrm{3}}$-PTCDA-Alq$_{\mathrm{3}}$ and PTCDA-Alq$_{\mathrm{3}}$-PTCDA, engineered to give index matching according to modeling. The waveguides were grown on a glass substrate via organic molecular beam deposition. Fabry-Perot oscillations observed from reflection measurements were used to confirm the individual layer thicknesses. We were able to observe refractive index matching between TE$_{\mathrm{0}}$ and TE$_{\mathrm{1}}$, as well as TE$_{\mathrm{2}}$ and TE$_{\mathrm{3}}$ modes for the PTCDA-Alq$_{\mathrm{3}}$-PTCDA waveguide due to the light propagation through the top and bottom PTCDA layers, respectively. In addition, we were able to match TE$_{\mathrm{1}}$ and TM$_{\mathrm{1}}$, as well as TE$_{\mathrm{3}}$ and TM$_{\mathrm{3}}$ modes in the Alq$_{\mathrm{3}}$-PTCDA-Alq$_{\mathrm{3}}$ multilayer due to the birefringence of the PTCDA layer. Furthermore, we are able to create mode matching for a range of wavelengths due to the similar effective refractive index dispersion of different waveguide modes. The ability to phase match different waveguide modes opens a wide range of potential applications including polarization-insensitive propagation and mode switching by adding a thin magnetic metal film within the waveguide and applying an external magnetic field. [Preview Abstract] |
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M1.00057: Electrical characterization of the light induced degradation in CH3NH3PbI3 thin film Bizuneh Gebremichael Difer, Genene Tessema Mola, Sentayehu Yigzaw Recently, organic metal halide perovskites have emerged as one of the most promising photoactive materials in the field of photovoltaics. Different reports shows that CH3NH3PbI3 based perovskite solar cells (PSCs) have got a power conversion efficiency of up to 20{\%}. However, Perovskites suffer inherent instability and degrade rapidly when exposed to an ambient operating atmosphere which limits their further application to commercialization. Several studies have been carried out to resolve this problem to some extent. Proper encapsulation of the device prevents from degradation due to moisture and oxygen. However, degradation due to light irradiation is difficult to manage. Recent studies demonstrated that in the steady state operation of the device, the Voc is unchanged by continuous illumination of light. Rather the reduction in the power conversion efficiency follows the trend of the Jsc. In this work, the effect of light on the electrical conductivity of the CH3NH3PbI3 thin film which is deposited on a glass substrate is investigated using a four point probe conductivity measurement. Further, the temperature dependent conductivity measurement demonstrated that the dominant conduction type in the film is electronic rather than ionic type. [Preview Abstract] |
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M1.00058: Surface Plasmon Peak Resonance Discovered in Sulfuric Acid Treated PEDOT-PSS Conductive Polymers Wil Andahazy, Ashleigh Baber, Costel Constantin Poly(3,4-ethylenedioxythiophene) poly(4-styrenesulfonate) (PEDOT-PSS) is one of the most promising transparent conductors which has applications in flexible electronics including organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field transistors (OFETs). Recently, scientists discovered that post-treatment with sulfuric acid of PEDOT-PSS thin films result in electrical conductivity increase and a UV absorption decrease due to the replacement of majority of PSS with sulfate ions (SO$_{4}$$^{2-}$). However, the optical properties of the acid treated PEDOT-PSS thin films are not very well understood. In this project, PEDOT-PSS thin films were deposited by either drop casting or spin coating onto microscopic slides, and then submerged into sulfuric acid for 10 minutes. We performed optical spectroscopy by using a HS-190 variable angle spectroscopic ellipsometer with a wavelength range of 200-2500 nm, and for the electrical properties we used a homemade van der Pauw set up. Our preliminary dielectric constants measurements show the existence of a plasmon resonance peak (PRP) present at $\sim$ 1100 nm. We will discuss the correlation between the PRP position and film thickness. [Preview Abstract] |
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M1.00059: Electrospinning Technique for Organic Semiconductive Polymers Composites Coaxial Nanofibers for Electronic Devices William Serrano Garcia, Sylvia Thomas This work is motivated by the need of new 1D structures for organic flexible electronic devices that does not rely on silicon. Formation of organic semiconductors coaxial p-n junctions and sensors using the electrospinning technique will be studied. Actual progressions in coaxial fibers lead to an advance in the usage of fibers in many fields, but, for the first time, two organic semiconductor polymers will form a p-n junction in a coaxial nanofiber structure, expecting functional diodes in the 100 nm range in diameter. Semiconducting polymers as P3HT and BBL, p- and n-type respectively, will be studied under the presence of UV radiation and organic gases. Is been shown in recent research on single fiber and fibrous electrospun p-n junctions shows an ideality factor of 2 and less when rectifying signals. Also, with high surface area to volume ratio can serve not only as a single fiber sensor but as a yarn sensor enhancing the sensitivity of the device. In regards to organic semiconducting coaxial p-n junction nanofibers, no reported studies have been conducted, making this study fundamental and essential for organic semiconducting flexible nanodevices. [Preview Abstract] |
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M1.00060: Role of Hydrogen Bonding on Nonlinear Mechano-Optical Behavior of $L$-Phenylalanine-based Poly(ester urea)s. Keke Chen, Jiayi Yu, Gustavo Guzman, S. Shams Es-haghi, Matthew L. Becker, Miko Cakmak The uniaxial mechano-optical behavior of a series of amorphous $L$-phenylalanine-based poly(ester urea) (PEU) films was studied in the rubbery state using a custom real-time measurement system. When the materials were subjected to deformation at temperatures near the glass transition temperature ($T_{\mathrm{g}})$, the photoelastic behavior was manifested by a small increase in birefringence with a significant increase in true stress. At temperatures above $T_{\mathrm{g}}$, PEUs with a shorter diol chain length exhibited a liquid-liquid ($T_{\mathrm{ll}})$ transition at about 1.06 $T_{\mathrm{g}}$ (K), above which the material transforms from a heterogeneous ``liquid of fixed-structure'' to a ``true liquid'' state. The initial photoelastic behavior disappears with increasing temperature, as the initial slope of the stress optical curves becomes temperature independent. Fourier transform infrared spectra of PEUs revealed that the average strength of hydrogen bonding diminishes with increasing temperature. For PEUs with the longest diol chain length, the area associated with N-H stretching region exhibits a linear temperature dependence. The presence of hydrogen bonding enhances the ``stiff'' segmental correlations between adjacent chains in the PEU structure. As a result, the photoelastic constant decreases with increasing hydrogen bonding strength. [Preview Abstract] |
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M1.00061: On Polydimethylsiloxane-Polyethylene Oxide Blends Alan Perez, Alin Cristian Chipara, Pulickel Ajayan, Dorina Chipara, Chandra Sekhar Tiwary, Robert Vajtai, Mircea Chipara Polyethylene oxide (PEO) is an unique polymer, being soluble both in water and in organic solvents. Some authors, consider PEO as an amphiphilic polymer that contains both hydrophilic and hydrophobic entities. Polydimethylsiloxane (PDMS) is the polymer with the most flexible polymeric chain. The contact angle water-PDMS ranges between 90 to 150$^{\mathrm{o}}$ with a tendency to decrease slowly in time. The polymeric mixture PDMS-PEO is expected to show unique properties due to the entanglement of the PDMS macromolecular chain around the PEO chain, with surface contributions derived from the interactions between the hydrophobic PDMS and hydrophilic groups of PEO. PEO-PDMS mixtures have been obtained by using 2 paths: The first one consisted in the direct mixing of PEO powder with PDMS and the other the dissolution of PEO in water, followed by the addition of PDMS, mixing by stirring and sonication followed by solvent removal. Raman spectroscopy was used to assess molecular motions. Microscopy investigations are aiming at the morphology of these mixtures. DSC studies focused on glass, melting, and crystallization phase transitions in the PEO component are reported. [Preview Abstract] |
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M1.00062: Investigation of hydrophobic interactions mediating the self-assembly of supramolecular host/guest polymer complexes utilizing Simultaneous Multiple Sample Light Scattering (SMSLS) Molly Payne, Curtis Jarand, Scott Grayson, Wayne Reed While living systems spontaneously heal injuries, most man made materials cannot recover from damage. Incorporating self-healing properties into synthetic polymers could significantly extend product lifetime, safety, and applications. Most reported approaches to incorporate healing into synthetic materials, however, require external stimuli such as chemical additives, heat, and light exposure. Although dynamic bonds have been explored, particularly using a hydrogen bond motif, this has not been fully investigated in an aqueous environment. To address this, hosts and guests that dynamically associate in water have been investigated to build aqueous self-healing materials. These association values were probed for various host/guest complexes using Simultaneous Multiple Sample Light Scattering (SMSLS), a technique that measures the size of aggregates via light scattering while varying concentration and other environmental factors. [Preview Abstract] |
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M1.00063: All-Cellulose Composites of Nanofibril and Molecular Cellulose Doug Henderson, Xin Zhang, Yimin Mao, Liangbing Hu, Robert Briber, Howard Wang Cellulose nanofibrils (CNFs) are the basic structural elements of most cellulosic materials; they show excellent mechanical characteristics due to a high crystallinity. Molecular solutions of cellulose (MSC) with no apparent aggregation are produced with an ionic liquid and dimethyl sulfoxide (DMSO) binary solvent mixture. Cellulose dissolution occurs by maintaining a 3:1 molar ratio of ionic liquid to cellulose sugar units. The use of DMSO minimizes the amount of ionic liquid used and allows control over viscosity. In this study, all-cellulose nanocomposites of CNFs and regenerated cellulose from MSC have been fabricated by co-precipitation. CNFs with average diameters of 2.5$+$/-0.5 nm and lengths of 300$+$/-100 nm were initially dispersed in water, then suspended in DMSO by solvent exchange and then mixed with MSC. The resultant mixtures were used to cast nanocomposite thin films. The microstructure of the films was studied using optical, atomic force, and electron microscopy which show an even dispersion of CNFs within the regenerated cellulose. Water-uptake behavior was investigated using small angle neutron scattering. The nanocomposite films show higher water resistance compared to neat NFC films and similar to that of cellulose regenerated from MSC. [Preview Abstract] |
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M1.00064: Small-angle Neutron Scattering Study on Cellulose Nanocrystal Solution: Phase Behavior and Magnetic Alignment Yimin Mao, Xin Zhang, Doug Henderson, Howard Wang, Robert Briber Cellulose nanocrystals (CNC) were prepared using a sulfuric acid hydrolysis method. CNC dispersions were characterized using small-angle neutron scattering (SANS) technique at both single particle and concentrated suspension levels. The former revealed a parallelepiped particle shape with a length of $\sim$150 nm, and the cross-sectional dimensions of $\sim$3$\times$20 nm. The CNC dispersion showed lyotropic liquid crystal behavior which could be qualitatively described by Onsager's model for rod-like particle solution. Between CNC concentrations (mass fraction) of $\sim$6\% to $\sim$8\%, the homogenous solution spontaneously phase separated into a dense phase having birefringence, and an optically isotropic phase. The birefringent phase showed chiral nematic characteristics under polarized microscope, with chiral pitch distance on the micron scale; with inter-particle distances of $\sim$40 nm, as revealed by SANS. The CNC stacking can be quantitatively examined using a 1D para-crystal model. Under weak magnetic field (0.4 T), the chiral nematic stack in the birefringent phase can be re-oriented with the pitch direction aligned with the magnetic field. The isotropic phase cannot be aligned under weak magnetic field. [Preview Abstract] |
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M1.00065: Effect of Water on Cellulose -- EMIM Ac -- DMSO Solution Xin Zhang, Yimin Mao, Doug Henderson, R. M. Briber, Howard Wang Mixtures of ionic liquids (IL) and polar aprotic solvents are found to be effective for dissolving cellulose to form a molecular solution. Cellulose is naturally hygroscopic and water is generally detrimental to the processing of cellulose using ionic liquids. It is important to understand the role of water in the dissolution and processing of cellulose. The effect of water on the dissolution process of cellulose in the solvent mixture -- DMSO - 1-Ethyl-3-methylimidazolium acetate (EMIM Ac) has been examined by polarized microscopy, small angle neutron scattering (SANS), small angle X-ray scattering (SAXS) and cloud point measurements. It was found that the presence of small amounts of water led to clustering of cellulose that could be disrupted by increasing temperature. However at high cellulose concentration, addition of water can facilitate the formation clear solutions and gels. Liquid crystalline behavior was observed in solutions with \textasciitilde 1{\%}wt of water and \textasciitilde 20 {\%}wt of cellulose. A structural repeat distance around 1.2 nm has been observed by SAXS, presumably from the alignment of cellulose chains. Phase diagrams of the solutions will also be presented. [Preview Abstract] |
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M1.00066: Programing Performance of Silk Fibroin Materials by Controlled Nucleation Zhengwei Chen, Honghao Zhang, Zaifu Lin, Youhui Lin, Jan H. van Esch, Xiangyang Liu To examine the mechanism of the network formation of silk fibroin (SF), we adopt mono-dispersed colloidal particles (MDCPs) as well defined foreign substrates to quantify their effect on the primary nucleation of $\beta $-crystallites in molecular networks (silk nano-fibrils) and the hierarchical network formation of SF. It follows that MDCPs are capable of accelerating the SF gelation by reducing the multi-step nucleation barrier, which gives rise to a high density of silk fibril domain networks due to the increase of primary nucleation sites. Consequently, through governing the change in the hierarchical mesoscopic structure, the macroscopic performance of silk materials can be controlled directly. As SF hydrogels represent a typical example of weak fibril domain-domain network interactions, the increase of fibril domain density leads to weaker gels. On the other hand, SF fibers correspond to strong fibril domain-domain network interactions, the increase of fibril domain density ends up with much tougher fibers. The knowledge obtained not only provides a facile strategy in controlling the structure and performance of SF materials, but also offers some useful routes to design and functionalize soft materials in general. [Preview Abstract] |
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M1.00067: Monitoring the degrafting of polyelectrolyte brushes by using surface gradients Yeongun Ko, Jan Genzer Polymer brushes comprise densely grafted polymer chains on surfaces, which possess high stability and high concentration of reactive centers per unit area compared to physisorbed polymer film. Polymer brushes are employed in many applications, including anti-fouling surfaces, cell adhesive surfaces, responsive surfaces, low-friction surfaces, etc. Recently, researchers reported that charged (or chargeable) polymer brushes can be degrafted from substrate while incubated in buffer solutions. Based on previous experiments conducted in our group and by others, we assume that chain degrafting results from the hydrolysis of Si-O groups in head-group of the initiator and/or the ester groups in main body of the initiator. The kinetic of hydrolysis is affected by mechanical forces acting on the initiator. Those forces depend on the molecular weight and the grafting density of the brush, and the concentration and distribution of charges along the macromolecule (tuned by pH - for weak electrolytes - and concentration of external salt). In this work, we study the stability of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes in two solvents (ethanol and water) at various pH values in water and under different levels of external salt concentration. [Preview Abstract] |
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M1.00068: Mechanophore activation in a crosslinked polymer matrix via instrumented indentation Chelsea Davis, Jeremiah Woodcock, Ryan Beams, Muzhou Wang, Stephan Stranick, Aaron Forster, Jeffrey Gilman Recent advances in mechanically-activated fluorophores will enable a host of unique scientific challenges and opportunities to be addressed. Several mechanophores (MPs) in polymers have been reported, yet the specific deformation required to activate these molecules in a bulk polymer network has not been sufficiently specified. In an effort to develop the mechano-activation/deformation relationship of a spirolactam-based MP, scratches were applied to a MP-functionalized glassy crosslinked material at varying normal loads and lateral displacement rates. This experimental design allowed strain and strain rate effects to be decoupled. The fluorescence activation was then observed. Areas of elastic and plastic deformation as well as brittle fracture were observed within each scratch as the normal loading of the indenter increased. The fluorescence intensity increased while the fluorescence lifetime decreased with increasing strain. Hyperspectral imaging revealed that the peak emission wavelength remained constant in the damage zone relative to the undeformed material. Contact mechanics models are employed to demonstrate that relatively high degrees of strain are required to initiate the ring-opening activation transition within the spirolactam-based MP. These self-reporting damage sensors can be incorporated within polymeric coatings to allow real time structural health monitoring for a myriad of applications. [Preview Abstract] |
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M1.00069: Adhesion of Au Thin Films on PMMA and Other Substrates Yvonne Kinsella, Luis Royo-Romero, Wm. Chris Hughes, Brian Augustine, Xiaofeng (Harry) Hu The adhesion of Au onto polymer surfaces has important applications in the aerospace and automotive industries, microelectronics, and the fabrication of microfluidic devices. Au is desirable for such applications due to its corrosion resistance as well as its excellent conductivity of heat and electricity. Unfortunately, the inertness of gold results in a poor adhesion to polymer surfaces such as PMMA. In previous work in our lab we have developed a method to quantify exactly how well Au adheres to PMMA. Thin layers (approx. 10-20nm) of Au are deposited onto 1in square pieces of PMMA and then polished with increasing amounts of pressure until the Au is removed. After each polishing step, the transparency of the Au film is determined by using a UV/Vis spectrophotometer or by counting the pixels after scanning a photo of the sample. In this study we have expanded to apply this method to Au thin films on glass, as well as Au/Cr thin films on glass. Testing glass is the first step towards testing other polymer substrates than PMMA, which will be equally as useful to the aforementioned applications. [Preview Abstract] |
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M1.00070: Dual-responsive soft actuators based on self-assembled polymers Seung Jae Kim, Moon Jeong Park Electroactive polymer actuators (EAPs) have been extensively studied for biomimetic technologies such as artificial muscles and soft robotics. While a large deformation can be achievable from EAPs under relatively low-driving voltages, the slow response time has long been a fundamental drawback of EAPs. Here, we investigate a new soft actuator capable of responding two different external stimuli. The actuator is composed of electroactive polymer and light-responsive polymer. We have employed ionic block copolymers having well-connected ion-conduction channels to raise response to electric-field. Light-responsive polymers were additionally incorporated into them to control the deformation of the actuator in an independent manner. Noteworthy observation in the present study is that the dual-responsive polymers resulted in synergetic achievement of high bending strain and fast response time, which marked a significant improvement from the conventional EAPs. [Preview Abstract] |
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M1.00071: PDMS-co-PVMS Copolymer Synthesis for Microfluidic Devices Arissa Baiamonte, Devin Nguyen, Baraka Lwoya, Giovanni Kelly, Julie N. L. Albert Poly (dimethylsiloxane) (PDMS) is the predominant material used for the fabrication of microfluidic devices because it is an easily synthesized, biocompatible, and flexible material that forms a good seal with other surfaces. However, PDMS is chemically inert and therefore difficult to functionalize for targeted applications, it can swell in the presence of organic solvents, and it can contaminate microfluidic solutions with unreacted oligomers. Therefore, my research goal is to synthesize random copolymers of PDMS and poly (vinylmethylsiloxane) (PVMS) that retain the benefits of PDMS and can be functionalized easily via thiol-ene click reactions. In the first stage of this work, dichlorodimethylsilane and vinylmethyldichlorosilane were each reacted with water to produce n-membered dimethylsiloxane rings and n-membered vinylmethylsiloxane rings, respectively. In the next step, polymers are synthesized by reacting these rings with potassium hydroxide and heat to form PDMS, PVMS, and PDMS-co-PVMS copolymers. Several reaction conditions have been tested to determine the kinetics and to relate molecular weight of the polymer or copolymer to reaction time. The polymer is then cross-liked through hydroxyl end groups with vinylmethoxysiloxane homopolymer (PVMES) cross-linker, tin catalyst, and heat. Once the polymer is cross-linked, the surface can be modified via thiol-ene click reaction to provide a diversity of surface functionality for microfluidic device applications. In the present work, we functionalize with a fluorinated thiol to impart solvent resistance. [Preview Abstract] |
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M1.00072: Preparation of high purity linear and cyclic poly($\varepsilon $-caprolactone) to demonstrate physical and thermal properties. Farihah Haque, Ricardo Perez, Juan Lopez, Scott Grayson, Alejandro Mueller Cyclic polymers are differentiated from more common linear polymers by their ring-like topology and lack of chain ends. Unlike linear counterparts, cyclic polymers are characterized with many unique properties including reduced hydrodynamic volume, improved thermal stability, and reduced domain spacing in self-assemblies. Improved synthetic techniques utilizing controlled polymerizations, quantitative click reactions, and preparative GPC have enabled the production of high purity linear and cyclic poly($\varepsilon $-caprolactone) (PCL) analogs. To date, cyclic PCL is known to exhibit increased rates of crystallization and the formation of more thermodynamically stable crystals. Since then, blends of linear and cyclic PCL have demonstrated unique thermal properties, deviating from the aforementioned trend, suggesting possible threading of linear within the cyclic. The work herein aims to continue exploring this unique phenomenon of cyclic polymers and to further develop an understanding of their structure-property relationships. [Preview Abstract] |
(Author Not Attending)
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M1.00073: Threading events in ring polymer melts: a detailed geometric analysis and their connection with the slow relaxation modes Vlasis Mavrantzas, Dimitrios Tsalikis, Dimitris Vlassopoulos We will present results from a detailed geometric analysis of atomistic configurations of ring polyethylene oxide melts accumulated in the course of very long molecular dynamics (MD) simulations at $T=$413K and $P=$1atm which allowed us to locate ring-ring threading events and quantify their strengths and survival times. We have identified a variety of threading situations and studied their dependence on ring molecular weight. We have found that threadings can last up to several times the corresponding ring relaxation time, which can explain (at least in part) the appearance of slow relaxation modes observed experimentally in entangled polymer rings [2]. We confirm this by proposing a new expression for the stress relaxation modulus of entangled polymer rings that is found to provide excellent fits to experimentally measured curves. [1] D.G. Tsalikis, V.G. Mavrantzas, D. Vlassopoulos, \textit{ACS Macro Lett.} 5, 755 (2016). [2] M. Kapnistos, M. Lang, D. Vlassopoulos, W. Pyckhout-Hintzen, D. Richter, D. Cho, T. Chang, M. Rubinstein, \textit{Nature Materials} 7, 997 (2008). [Preview Abstract] |
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M1.00074: The Effect of the Size and Type (Dimensionality) of Carbon Nano-Fillers on the Optical Propertes of of Polystyrene Composites. Adnan Jaradat A set of samples of polystyrene composites with Multi-wall carbon nanotubes (MWCNTs), Graphene nanosheets, and Carbon Black nanospheres (CB) have been prepared with concentrations from 0.01{\%} up to 0.05{\%} using casting technique. The effect of type and dimensionality of the nanofiller on the optical properties of polystyrene composite have been studied. The optical absorbance, reflectance and transmittance were recorded using UV-VIS in the wave length range 290 to 700nm. The results of this study show that films with Multi-Wall Carbon Nanotubes (MWCNTs) filler have the highest refractive index, while films with Carbon Black (CB) filler have the lowest refractive index. The estimated optical band gap was found to depend on the type and dimensionality of the filler with values range between 4.15eV to 3.90eV. The dielectric constant has been calculated using the optical measurements. The study show that lower the dimensionality of the filler gives the highest value of the dielectric constant. [Preview Abstract] |
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M1.00075: Conducting polymer-metal nanoparticle composites with controlled dimensionality Kyoungwook Kim, Moon Jeong Park Conducting polymers have extensively been studied for diverse applications such as electronic devices and energy conversion systems owing to their high electrical conductivity and low-temperature processing conditions. Particularly, the composite materials composed of conducting polymers and metal nanoparticles have become increasingly important to increase their functionalities. In the present study, we synthesize the conducting polymer/metal nanoparticle composites and demonstrate the importance of controlling the dimensionality of resultant materials to enhance electrical conductivity. Two-dimensional conducting polymers prepared on ice surfaces showed the long-range ordered edge-on $\pi $-$\pi $ stackings that offer well-arranged molecular sites for nucleating nanocrystals with high density. This enabled us to achieve high redox catalytic activity, which marked a significant improvement from the literature. [Preview Abstract] |
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M1.00076: Kinetic View of Nanoparticle Assemblies in Supramolecular Nanocomposite Thin Films Jingyu Huang Nanocomposite thin films containing hierarchically structured nanoparticle (NP) assemblies are ideal candidates for the fabrication of metamaterials. However, when the particle and polymer chain have similar feature sizes, macrophase separation between the polymers and NPs are usually observed. Controlling NP diffusivity in polymer matrix provides an opportunity to control the kinetic pathways for NP assembly and to access 3-D NP assemblies in non-equilibrium states. Here, we present the thin film 3-D hierarchical assembly of NPs in block copolymer-based supramolecular thin films under solvent vapor annealing (SVA) by varying the ratio between the particle size and suparmolecule periodicity. By manipulating the NP diffusion kinetics in the supramolecular matrix, surface aggregation of NPs was suppressed and NPs co-assembled with supramolecules to form 3-D morphologies in thin films. The present studies opened a viable route to construct functional composite thin films containing large nanoparticles via kinetic control. [Preview Abstract] |
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M1.00077: Novel Technique for Quantitative Fast Scanning Calorimetry on Electrospun Fibers David Thomas, Nelaka Govinna, Christoph Schick, Peggy Cebe Fast scanning chip calorimetry allows for the study of polymers which have rapid nucleation and/or crystallization kinetics, or degrade within their melting range. Heating rates used, up to 4000 K/s, allow studies of hetero and homogeneous nucleation at time scales inaccessible with conventional calorimeters, whose rates are typically \textless 0.5 K/s. Polyethylene terephthalate (PET) and polyvinyl alcohol (PVA) were chosen in the development of a new methodology to obtain quantitative fast scanning thermal data from electrospun nanofibers using a Flash DSC1. The structure of nanofibers requires special methods to load nanogram-sized samples onto a UFSC1 sensor. Fibers were directly spun onto TEM grids which provide a durable substrate to support bundles of nanofibers and possess excellent thermal conductivity allowing for a strong, repeatable signal and ensure good sample to sensor contact. As spun samples were held isothermally at temperatures ranging from T$_{\mathrm{g}}$ to T$_{\mathrm{m}}$ then heated at 2,000 K/s to assess as-spun crystallinity and cold crystallization behaviors. Above T$_{\mathrm{m}}$ the fibers break up into micro- and nano-droplets. On these samples, melt crystallization experiments were performed to study nucleation and crystallization of polymer confined to nanodroplet morphology. [Preview Abstract] |
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M1.00078: Investigation of polymorphism for amorphous and semi-crystalline poly (-ethylene terephthalate-) using high-pressure Brillouin spectroscopy Jonghyun Song, Young-Ho Ko, Muhtar Ahart, Jae-Hyeon Ko High-pressure Brillouin spectroscopy was applied to clarify quantitatively the physical and mechanical difference of a polymer with distinct structures consisting of the same elements. The pressure dependences of elastic properties, Young's modulus, shear modulus, bulk modulus, and Poisson's ratio for an amorphous poly (-ethylene terephthalate-) [(-PET-)] and a semi-crystalline PET were compared for pressures up to 10 GPa. A collapse of free volume for two PETs was ascertained at the different value of pressure with different slopes of elastic properties, Young's modulus, shear modulus, and bulk modulus. Although the Poisson's ratios of a semi-crystalline PET increased linearly upon the pressure, those of an amorphous PET were almost constant. The P-V equation of state (EOS) for an amorphous PET was also determined and their isothermal bulk moduli extracted from Birch- Murnaghan and Vinet EOS were 6.3 GPa and 6.7 GPa, respectively. [Preview Abstract] |
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M1.00079: Nanostructured functional hybrid materials via self-assembly of brush block copolymers Dong-po Song, Yue Gai, Benjamin Yavitt, James Watkins The self-assembly of well-ordered nanoparticle (NP) / block copolymer (BCP) composites enables precise control over the spatial distribution of NP arrays, providing a simple route to the low-cost ``bottom-up'' fabrication of hybrid materials with enhanced mechanical, optical and electric properties. Here we summarize the fabrication of nanocomposites via the self-assembly of brush BCPs (BBCPs). In comparison to conventional materials based on linear BCPs, the BBCP hybrids exhibit many attractive features, including rapid supramolecular self-assembly (\textless 5 min), macroscopic ordering, large lattice parameters (\textgreater 100 nm), and high loading of functional additives (\textgreater 70 wt{\%}). Both the self-assembled structures and the compositions of the nanocomposites can be widely tuned for applications such as photonic crystals or coatings, nonlinear optics, and metamaterials. In addition, BBCPs were employed as templates for the mesoporous hybrid materials that have large mesopores (up to 40 nm) and high loadings of functional NPs (up to 50 wt{\%}). Simple solutionbased processing and rapid self-assembly of brush BCP nanocomposites are promising for roll-to-roll manufacturing of low-cost and flexible devices. [Preview Abstract] |
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M1.00080: Using in-Situ Ellipsometry to Monitor Self-Assembly of Polymer Nanocomposites during Solvent Annealing Melissa J. Vettleson, Chen Li, Ethan C. Glor, Robert C. Ferrier, Russell J. Composto, Zahra Fakhraai The solvent vapor annealing (SVA) process can efficiently drive the self-assembly of block copolymers and polymer nanocomposites (PNCs); a variety of morphologies and arrangements may be achieved. Unfortunately, due to a lack of simple and effective in-situ characterization methods, little is known of the details of the process. We have developed an in-situ method of analyzing dispersity and orientational anisotropy of gold nanorods as well as other anisotropic nanoparticles in PNCs using spectroscopic ellipsometry. This method can be used to track changes in PNC films during the SVA process. While monitoring changes in the thickness and optical properties of the films in-situ, we assess the changes in particle arrangement and alignment due to the swelling process by tracking the changes in the sample’s index of refraction and optical birefringence. Using this method we study the effect of brush/media interactions on the final dispersion state and study the effects of both swelling and drying processes on the kinetically trapped states of dispersion in PNC samples. [Preview Abstract] |
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M1.00081: Raman Investigations on PVC-Functionalized Single Wall Carbon Nanotube Composites. Jorge Cisneros, Dorina Chipara, Elamin Ibrahim, Mircea Chipara Polyvinylchloride (PVC) is a widely used polymer whose applications are limited by poor thermal and flame stability. Nanofillers typically enhance the thermal stability and reduce flammability of polymers. Composites containing PVC loaded by COOH functionalized SWNT (PVC-fSWNT) have been obtained by solution mixing. The polymeric matrix was dissolved in THF, the nanofiller was added to the solution, and the as obtained mixture was sonicated for 1 hour. The solvent has been evaporated by heating at 90~oC in an oven for about 12 hours. The concentration of fSWNT ranged from 0 \textbraceleft $\backslash ${\%}\textbraceright wt. up to 20 \textbraceleft $\backslash ${\%}\textbraceright wt. Thermo gravimetric analysis (TGA) has been performed by using a TA instrument Q500 operating at various heating rates (ranging from 10 to 50~oC/min) from 50~oC to 1000~oC. Measurements have been performed by using a Renishaw InVia confocal Raman microscope, equipped with lasers operating at 432 and 785 nm. The analysis is focused on the effect of polymeric matrix on the fSWNT lines and on the modifications of the Raman lines assigned to the polymeric matrix. Raman measurements on PVC-fSWNT nanocomposites thermally degraded in air in the temperature range 50 to 300~oC are reported. [Preview Abstract] |
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M1.00082: Chain-Scale Polymer Dynamics Through Homogeneously Confining Nanoparticles Eric Bailey, Huikuan Chao, Robert A. Riggleman, Karen I. Winey The addition of nanoparticles (NPs) to a polymer matrix can significantly enhance polymer mechanical and functional properties. Recent tracer diffusion experiments in nanocomposites show that polymer diffusion is significantly reduced relative to the bulk. In fact, a master curve was developed by plotting diffusion coefficients normalized by that of the bulk polymer against the confinement parameter, ID/2Rg, where ID is the interparticle distance and Rg is the tracer size. To further study the role of confinement, coarse-grained MD simulations are used to systematically study the independent effect of ID and Rg on chain-scale dynamics. A uniquely constructed simulation box with a monolayer of hexagonally packed NPs creates regions of homogeneously confined polymer and pristine bulk polymer. This reveals the magnitude and length scale of NP-induced perturbations for several values of ID/2Rg. Displacement distributions show significant asymmetries in polymer motion near NPs and localized diffusion coefficients show more than a 25{\%} reduction in diffusion coefficient. Surprisingly, chain dynamics are perturbed several times Rg from the NP region. These MD simulations are then compared to calculations on a minimal model in the same simulation environment. [Preview Abstract] |
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M1.00083: Coarse-grained simulation of polymer-filler blends Gregg Legters, Vikram Kuppa, Gregory Beaucage The practical use of polymers often relies on additives that improve the property of the mixture. Examples of such complex blends include tires, pigments, blowing agents and other reactive additives in thermoplastics, and recycled polymers. Such systems usually exhibit a complex partitioning of the components. Most prior work has either focused on fine-grained details such as molecular modeling of chains at interfaces, or on coarse, heuristic, trial-and-error approaches to compounding (eg: tire industry). Thus, there is a significant gap in our understanding of how complex hierarchical structure (across several decades in length) develops in these multicomponent systems. This research employs dissipative particle thermodynamics in conjunction with a pseudo-thermodynamic parameter derived from scattering experiments to represent polymer-filler interactions. DPD simulations will probe how filler dispersion and hierarchical morphology develops in these complex blends, and are validated against experimental (scattering) data. The outcome of our approach is a practical solution to compounding issues, based on a mutually validating experimental and simulation methodology. [Preview Abstract] |
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M1.00084: Block Copolymer Directed Biomimetic Mineral Formation for Polymer Nanocomposites Sarah Gleeson, Tony Yu, Xi Chen, Michele Marcolongo, Christopher Li Bone is a hierarchically structured biocomposite comprised of mineralized collagen fibrils. The mechanical properties of bone can be precisely tuned by the structure and morphology of the mineral nanocrystals as well as the organic collagen fibrils. Synthetic materials that can mimic the nanostructure of natural bone show promise to replicate bone's structural function, yet little is known about the mechanism of mineral formation. We previously have shown that hierarchically ordered polymer fibers control the distribution and orientation of hydroxyapatite, enhancing mechanical properties and biocompatibility. We demonstrate a new method for mineralization by forming block copolymer single crystal films of polycaprolactone-\textit{block-}poly(acrylic acid) (PCL-$b$-PAA) so that lamellar anionic PAA nanodomains recruit mineral ions and provide one-dimensional confinement to induce orientation. The effect of the anionic domain dimensions on mineral content, orientation, and structure within the polymer matrix is shown. The mechanical properties of the nanocomposite are evaluated to determine the role of mineral orientation and crystallinity in composite strength. These results can be used to tailor the physical mineralization environment to create a more biomimetic bone material. [Preview Abstract] |
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M1.00085: Large nanoparticle assembly in block copolymer-based supramolecules Yihan Xiao, Ting Xu Self-assembly of nanoparticles into 1-D, 2-D and 3-D nanostructures is promising for exploiting their collective properties. A significant challenge to realize their potential is to fabricate 3-D assembly of nanoparticles with designed structures and functionalities. Top-down approaches such as lithography are insufficient to generate hierarchical 3-D assemblies. Block copolymer (BCP) directed self-assembly, provides an alternative avenue to address these limitations, but is restrictive to nanoparticle size (d) to be below a fraction of BCP periodicity (D). The restriction in particle size prohibits the application of the method to nanoparticles with exciting size-dependent properties. We show that nanocomposites composed of block copolymer-based supramolecules and nanoparticles offer a platform to obtain nanostructured composites with single particle precision using nanoparticles in the size range of tens of nanometer. Excess small molecules are critical in preventing macrophase separation and achieving a d/D ratio up to 1.6. The supramolecular approach opens up a new route to overcome present challenges toward designer nanocomposites. [Preview Abstract] |
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M1.00086: Polymer Dynamics of Grafted Nanoparticle Composites. Steven Lee, Wei Peng, Rahmi Ozisik The viscoelastic properties of nanoparticles containing two types of grafted chain components in linear polymer composites were investigated via Molecular Dynamics simulations. Two component grafts were simulated at different graft densities and molecular weights using bead-spring model. Static and dynamic properties of graft and matrix chains were analyzed as a function of deformation parameters. Results are compared to experimental observations obtained from literature. [Preview Abstract] |
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M1.00087: The Effect of Charged Macromolecules on the Crystallization of Ionic Solutes during Solution Evaporation Seyoung Kim, Jewon Choi, Soo-Hyung Choi, Kookheon Char Charged macromolecules are crucial components in bio-mimetic crystallization as they modify size, shape, and the phase of ionic minerals, since the electrostatic binding between charged molecules and ionic mineral surface alters the surface energy in a specific crystallographic direction. We use poly(acrylic acid) (PAA) and block copolymer micelles (BCMs) containing polystyrene (PS) cores and PAA brushes as modifiers of CaSO$_{\mathrm{4}}$ hemihydrate crystals, which are grown through the evaporation of solution droplets. The evaporation at the air-liquid interfaces directs the nucleation and growth of crystallization to proceed locally near the interface. The addition of linear PAAs or spherical BCMs with the crystallizing mineral varied the dominant facet as well as the aspect ratio of the crystals. For the linear PAAs added, it is noted that the interference of crystallization becomes weak as the length of PAA is increased, while, for the BCMs added, the interference becomes weak as the ratio of PAA to PS blocks is decreased. Hence, the modification of crystal growth of minerals is largely dependent upon the bulkiness of charged objects, i.e., the conformational constraint of charged chains for the surface adsorption. [Preview Abstract] |
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M1.00088: Flattening process of polymer chains irreversibly adsorbed on a solid Mani Sen, Naisheng Jiang, Justin Cheung, Maya Endoh, Tadanori Koga, Daisuke Kawaguchi, Keiji Tanaka We report the structural relaxation process of irreversibly adsorbed polymer chains that lie flat on a solid (``flattened chains (FC)'') via thermal annealing. Amorphous polystyrene (PS) on quartz, which together constitute a weakly attractive system, was used as a model system and the local chain conformations of the FC were investigated by sum frequency generation spectroscopy (SFG). Two different film preparation processes (i.e., spin coating and dip coating) were used to create different initial chain conformations. PS films were annealed at T\textgreater \textgreater T$_{\mathrm{g}}$ to reach the ``quasiequilibrium'' state and subsequently rinsed with chloroform, a good solvent to uncover the buried FC. SFG results revealed that the backbone chains (constituted of CH and CH$_{\mathrm{2}}$ groups) of the FC preferentially orient to the weakly interactive substrate surface via thermal annealing regardless of the initial chain conformations, while the orientation of the phenyl rings becomes randomized. We postulate that increasing the number of surface-segmental contacts (i.e., enthalpic gain) is the driving force to overcome the conformational entropy loss in the total free energy. [Preview Abstract] |
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M1.00089: Self-organized structures of $\pi $-conjugated polymer chains at the solid-polymer interface Zhongjie Hu, Mani Sen, Levent Sendogdular, Maya K. Endoh, Tadanori Koga, Chang-Yong Nam The interfacial structure of poly(3-hexylthiophene) (P3HT) conjugated polymer on planar solid substrates was investigated by a combination of surface sensitive experimental techniques. 50 nm-thick spin-cast P3HT films were prepared on hydrogen fluoride etched Si substrates and then annealed at 170 $^{\circ}$ C for up to 100 h under vacuum. The films were then solvent-leached with chloroform repeatedly until the thickness of the residual layer remained unchanged. The X-ray reflectivity and atomic force microscopy experiments elucidated the formation of homogenous 3.5 nm-thick adsorbed P3HT layer on the Si substrate. Grazing incidence X-ray diffraction (GIXD) illuminated that the $\pi $-conjugated polymer chains in the absorbed layer still predominantly self-assembled into ``edge-on'' orientated lamella at the interface despite the reduced degree of the lamellar ordering compared with that of the original 50 nm-thick P3HT thin film. In addition, the interfacial structure of a P3HT:[6,6]-phenyl C$_{\mathrm{61}}$-butyric acid methyl ester (PCBM) blend film was studied by the same experimental strategy, and the details will be also discussed in the presentation. [Preview Abstract] |
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M1.00090: Tailoring ion transport to improve thermoelectric properties of mixed polymer thermoelectrics Shubhaditya Majumdar, Gabriel E. Sanoja, Nicole Michenfelder-Schauser, Colin R. Bridges, Rachel A. Segalman Polymer thermoelectrics show potential for simultaneously possessing high Seebeck coefficients and electrical conductivities by coupling electrochemical reactions at the electrodes with independent pathways for ion and electron transport. We show that by blending commercially-available PEDOT:PSS with a metal--polymer complex, the thermal diffusion of ions due to the Soret effect and the entropy of the electrochemical reactions can be leveraged to obtain Seebeck coefficients of O(10 mV/K). The transient behavior of the Seebeck coefficient in these systems can be systematically modified based on the nature of the ionic species. We describe the chemistry necessary to realize these phenomena in dry and ambient conditions and suggest future pathways to further optimize the figure of merit. These findings are an improvement over previous studies wherein such effects were demonstrated only in high-humidity environments, thus allowing us to perform detailed experimental analysis of the energy transport phenomena in such polymer thermoelectrics. [Preview Abstract] |
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M1.00091: Multiscale Simulations of PS-PEO Block Copolymers with LiPF$_{6}$ Ions in Lamellar Phase: Dynamics Vaidyanathan Sethuraman, Santosh Mogurampally, Venkat Ganesan Hybrid simulations, which include coarse-graining and inverse coarse-graining steps, are performed to characterize the dynamic properties of polystyrene-polyethylene oxide (PS-PEO) block copolymer (BCP) melt in the ordered lamellar phase doped with Li-PF$_{6}$ salt at the atomistic level. The ion dynamics in the block copolymer melts are studied as a function of salt concentration. Further, the ion dynamics are studied as a function of the distance from the interface to identify the spatial heterogeneity in ion dynamics. To identify the mechanism of ion transport, the inter- and intra- chain hopping are quantified. [Preview Abstract] |
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M1.00092: Structural properties of thiophenes investigated with simulations of a coarse-grained model Jutta Luettmer-Strathmann, Amani Almutairi Thiophenes have important applications in organic electronics, energy conversion, and storage. The interfacial layer of an organic semiconductor in contact with a metal electrode has important effects on the performance of thin-film devices. However, the structure of this layer is not easy to model. In recent work, we developed a coarse-grained model for alpha-oligothiophenes in the bulk and near gold surfaces. We describe the molecules as linear chains of bonded, discotic particles with Gay-Berne potential interactions between non-bonded ellipsoids. In this work, we investigate structural properties of thiophenes with simulations of our coarse-grained model. [Preview Abstract] |
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M1.00093: Lithium Metal Batteries Using Cross-linked Polymer Electrolytes: Importance of the Electrode/Polymer Electrolyte Interefaces Qiwei Pan, Dmitri Barbash, Christopher Li Lithium metal batteries (LMBs) are of high demand these days, since they show ten times higher of capacity when compared to the currently used graphite anode in the lithium ion batteries. However, the uneven deposition of lithium on the lithium metal which leads to growth of lithium dendrites that can short-circuit the cell is still a big problem for this technology. Nowadays, the all solid-state polymer electrolytes (SPEs) show their potential use in the LMBs due to their excellent lithium dendrite growth resistance and superior safety. In this work, a serious of cross-linked SPEs with different network structures are used in the LMBs with a LiFePO$_{\mathrm{4}}$ cathode. High performance LMBs with excellent rate capability and long cycle life can be obtained at 90 °C. Furthermore, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-Ray photoelectron spectroscopy (XPS) were firstly introduced to study these LMBs. For the first time, it is found that the interfaces of the cathode\textbar SPE and Li\textbar SPE play important roles in the stability of the polymer LMBs. It is also found that these interfaces are stable to temperature. The obtained LMBs show high performance at the medium temperature range. [Preview Abstract] |
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M1.00094: Sol-gel transition behavior of aqueous peptide-amphiphile (C16-W3K) solutions: effects of alkyl-tail length, mechanical shear, temperature, and salt Masashi Yamamoto, Takahiro Otsuka, Yoshinori Orimo, Tomoki Maeda, Atsushi Hotta Peptide amphiphiles (PA) possess nanoscale micelle structures and excellent biocompatibility. In aqueous PA solution, PA molecules can self-assemble through various configurations into spherical and wormlike micelles, which can occasionally form hydrogels. C16-W3K is one of the unique PA, whose micelle configurations can transfer from spherical to wormlike structures in its aqueous solution over time, while the wormlike micelles could also lead to gelation. In our recent research, the effects of the length of the hydrophobic alkyl tail and other external factors of C16-W3K on the gelation behavior of the C16-W3K solution have been discussed. It has been revealed that longer alkyl-tails could facilitate the gelation of the C16-W3K solution, and that the external stimuli, such as mechanical shear and heat, could promote faster gelation of the C16-W3K solution. It was also found that salt could adjust the pH of the C16-W3K solution, having profound influence on the gelation behavior of the C16-W3K solution. In fact, the gelation of the C16-W3K with a higher storage modulus could be obtained from relatively acidic solutions, while the gelation of the C16-W3K solution was firmly suppressed in highly basic solutions. [Preview Abstract] |
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M1.00095: Deformation Behavior of Monolayer Assemblies of Polystyrene Grafted Nanoparticles Yang Jiao, Ming-Siao Hsiao, Lawrence Drummy, Richard Vaia Assemblies of polymer-grafted nanoparticles (PGNs) are of interest to a wide array of structural, photonic and electrical applications. In contrast to nanoparticles dispersed in a free polymer matrix, the grafted polymer determines particle spacing. The extent to which these grafted polymers are entangled determines the robustness and strength. Here, we investigate the correlation between PGN architecture (nanoparticle radius, graft density, graft molecular weight) and the deformation mechanism of polystyrene-grafted PGNs. In contrast to highly stretched conformations within a dense brush of short chains, the canopy height, h, for PGNs with sparse grafting density (0.05 ch/nm2), scales as h $\approx $ N$^{1/3\, }$in as-cast films, and relaxes to h $\approx $ N$^{0}$ for annealed films. This implies densification and chain relaxation occur due to these volumetrically frustrated PGN designs. An increase in polymerization degree, regardless of grafting density, results in a conformational transition to semidilute polymer brush (SDPB), accompanied by an increase in fracture toughness. Overall, these studies of low graft density PGNs imply that a unique canopy architecture exists that optimizes the critical application requirement of simultaneous maximization of nanoparticle volume fraction and toughness. [Preview Abstract] |
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M1.00096: Free Surface Flows and Extensional Rheology of Polymer Solutions Jelena Dinic, Leidy Nallely Jimenez, Madeleine Biagioli, Alexandro Estrada, Vivek Sharma Free-surface flows -- jetting, spraying, atomization during fuel injection, roller-coating, gravure printing, several microfluidic drop/particle formation techniques, and screen-printing -- all involve the formation of axisymmetric fluid elements that spontaneously break into droplets by a surface-tension-driven instability. The growth of the capillary-driven instability and pinch-off dynamics are dictated by a complex interplay of inertial, viscous and capillary stresses for simple fluids. Additional contributions by elasticity, extensibility and extensional viscosity play a role for complex fluids.~We show that visualization and analysis of capillary-driven thinning and pinch-off dynamics of the columnar neck in an asymmetric liquid bridge created by dripping-onto-substrate (DoS) can be used for characterizing the extensional rheology of complex fluids. Using a wide variety of complex fluids, we show the measurement of the extensional relaxation time, extensional viscosity, power-law index and shear viscosity. Lastly, we elucidate how polymer composition, flexibility, and molecular weight determine the thinning and pinch-off dynamics of polymeric complex fluids. [Preview Abstract] |
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M1.00097: Coarse-Grained Simulations of 3D Printing Zilu Wang, Andrey Dobrynin 3D printing is a revolutionary manufacturing technique which makes it possible to fabricate a 3D object of any shape and size that is hard to make by traditional methods. We use coarse-grained molecular dynamics simulations to model the Continuous Liquid Interface Production (CLIP) 3D printing techniques. This technique utilizes a continuous curing of the liquid precursor by the UV light within a thin layer during pulling the crosslinked polymeric object out of a liquid pool. Our simulations show that the quality of the shape of the 3D printed objects is determined by a fine interplay between elastic and capillary forces. With decreasing the size of the printed features, the object shape deformations are controlled by optimization of the surface area of the exposed interface. This results in large deviations of the printed shape from the programed one. The high quality of the printed features is obtained when its size is larger than the elastocapillary length -- ratio of the surface tension and modulus of crosslinked polymeric material. The condition when size of the feature becomes comparable with the elastocapillary length could be considered as a resolution limit for this 3D printing technique. Using our simulation results we have identified the source of the object shape deformations and developped a set of rules for calibration of the parameters to meet the accuracy requirements. To improve printing quality we have redesigned the CLIP 3D technique. Our simulations show that the proposed modifications of the printing process could improve printing quality. [Preview Abstract] |
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M1.00098: Synthesis and characterization of polypeptide-Co3O4 nano-conjugates. Bithi Paul, Mahmud Reaz, Md Abdullah-Al Mamun, Adam Wanekaya, Robert Delong, Haribhua Gholap, Kartik Ghosh Nanoconjugates, composites of inorganic nanomaterials and biomolecules such as DNA, RNA, and proteins, establish sequences of a wide varieties nano-bio boundaries. The formation of these boundaries strongly depends on complex bio physicochemical reactions. Polypeptide nanostructures exhibit a unique type of self-assembled bio-material having many interesting properties and applications. Nanoparticles of Co3O4 exhibit ferromagnetism at room temperature. In this work, we are investigating structural and magnetic properties of polypeptide-Co33O4 nano-conjugates. Polypeptide nanotubes were made using Phenylalanine, diphenyl hexafluoride isopropanol, and deionized water using sol-gel method. The peptide tubes were hybridized with Co3O4 through the reduction of Co ions from CoCl2 aqueous solution and the heat treatment. SEM images show that polypeptide nanotubes are nicely decorated with inorganic nanoparticles. EDX data indicate conjugation between peptide nanotubes and Co3O4. To characterize the metallic oxide phase and the interface more prominently, nano-bio composites were probed using XRD, Raman spectroscopy, and magnetic measurement. This research work is supported by National Cancer Institute (1R15 CA139390-01). [Preview Abstract] |
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M1.00099: Composite reinforced metallic cylinder for high-speed rotation Dr. Sahadev Pradhan The objective of the present study is to design and development of the composite reinforced thin metallic cylinder to increase the peripheral speed significantly and thereby? improve the separation performance in a centrifugal gas separation processes through? proper optimization of the internal parameters. According to Dirac equation (Cohen? (1951)), the maximum separative work for a centrifugal gas separation process increases? with 4th power of the peripheral speed. Therefore, it has been intended to reinforce the? metallic cylinder with composites (carbon fibers: T-700 and T- 1000 grade with suitable? epoxy resin) to increase the stiffness and hoop stress so that the peripheral speed can? be increased significantly, and thereby enhance the separative output. Here, we have developed the mathematical model to investigate the elastic stresses of? a laminated cylinder subjected to mechanical, thermal and thermo-mechanical loading.? A detailed analysis is carried out to underline the basic hypothesis of each formulation.? Further, we evaluate the steady state creep response of the rotating cylinder and analyze? the stresses and strain rates in the cylinder. [Preview Abstract] |
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M1.00100: Semi-crystalline morphologies of linear and cyclic poly($\epsilon$-caprolactones) in the diffusion-limited film thickness regime Giovanni Kelly, Amelia Bergeson, Farihah Haque, Scott Grayson, Julie Albert Thin and ultrathin films of semi-crystalline polymers have been studied for decades due to their far-reaching applications including opto-electronic materials and biological studies of drug delivery and cell adhesion. This body of work has focused on every aspect of crystallization, from the fundamental thermodynamics and kinetics of crystal growth to methods for affecting crystalline morphologies via blending with other polymers. Due to significant synthetic challenges, one area where progress has lagged behind is the study of non-linear architectures, especially ring polymers. However, pioneering work by polymer chemists around the world has closed that gap, and we are beginning to observe important differences between ring and linear polymers in bulk materials. As a complement to those advances, this work aims to compare the morphologies of linear and cyclic poly($\epsilon$-caprolactones) (PCL) observed in heavily-confined ultrathin films where crystal growth is diffusion-limited. Understanding how confinement effects alter morphology will provide invaluable insight into differences in crystal growth as a function of molecular architecture. [Preview Abstract] |
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M1.00101: Synthesis and thin film morphology of linear and cyclic poly($\epsilon$-caprolactone) Amelia Bergeson, Farihah Haque, Giovanni Kelly, Scott Grayson, Julie Albert Polymers have a wide variety of applications in the scientific community as well as everyday life. Poly($\epsilon$-caprolactone) (PCL), a semi-crystalline aliphatic polyester, has found important applications including drug delivery devices. The procedure for synthesizing linear PCL is well-documented and thus linear PCL has been studied in various systems, including bulk and thin films. On the other hand, the ability to synthesize cyclic PCL has only recently been developed. The synthesis of cyclic PCL from the linear analogue can be accomplished via “click” chemistry. Characterization of thin films of cyclic PCL via atomic force microscopy and optical microscopy produced novel results with respect to morphology and crystallization kinetics. These observations are not limited to the pure cyclic thin films, but also appear in various blends of linear and cyclic PCL. [Preview Abstract] |
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M1.00102: Thermally induced lamellar reorganization and thickening in spherical poly (L-lactic acid) crystalsome Mark Staub, Hao Qi, Christopher Li Understanding fundamental aspects of spherical crystals is important for a variety of applications such as encapsulation and drug delivery. The curved nature of these crystals gives rise to differences in key crystallographic concepts such as grain boundaries and defect formation when compared to flat crystals. This curved crystallography is difficult to study experimentally, especially at the nanoscale. Our group has recently shown how an oil in water miniemulsion can be used to direct the crystallization of poly (L-lactic acid) (PLLA) at a curved liquid/liquid interface. This produces nanosized, polymer single-crystal-like capsules termed “crystalsomes” with increased stability and mechanical properties compared with non-crystalline counterparts. This system will serve as our model for examining spherical crystallography. In this work, combined wide angle X-ray diffraction, Atomic force microscopy, and differential scanning calorimetry is employed to examine how the curved interface effects crystal thickening and reorganization compared to flat PLLA crystals. The influence of degree of curvature on these processes is also studied by examining crystalsomes with differing diameters. [Preview Abstract] |
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M1.00103: Cholesteric networks for creation of Liquid Crystalline Nose (LCN). Petr Shibaev, Xiaoyurui Wang, Violet Guzman, Lee Vigilia, William Charles, Daniel Carrozzi Novel cholesteric siloxane polymers with mesogenic pendant groups were synthesized and studied for the detection of volatile organic compounds (ethanol, toluene, cyclohexane, and acetic acid). Cholesteric polymers have numerous advantages over low molar mass liquid crystals since they can be prepared as thin films and be very useful for fast visual detection of volatile organic compounds (VOCs). Interaction of VOCs with chiral polymers lead to changes of order parameter, twisting power of chiral dopants, and swelling of the polymer matrix. These effects result in a spectral shift of the selective reflection band of cholesteric polymers. The magnitude and direction of the spectral shift depend on the chemical structure of the VOC and the composition of cholesteric matrix. These effects are analyzed and discussed for different chemical structures of the matrix. The selectivity of response to different VOCs makes the creation of ``liquid crystalline nose'' (LC nose) not a distant possibility. [Preview Abstract] |
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M1.00104: Chain Folding and Lamellar Thickening Behavior in Polymer Crystallization based on self-consistent field theory Ping Tang, Faqiang Liu, Yuliang Yang Chain folding is a main characteristic in polymer crystallization which remains challenging in theoretical investigations, due to its spanning from the microscale of chain segment and mesoscale of entire chain trajectory in lamellae. The self-consistent field theory (SCFT) based on multi-block rod-coil chain model is employed to investigate the crystalline behavior. The chain conformation in the crystalline and amorphous regions is described with Caussian chain and rigid rods. The results indicate that lamellae thickness and the proportion of adjacent re-entry conformation depend on the combined effect of crystalline enthalpy, spatial distribution in amorphous region, and interfacial energy resulting from fold energy and conformation loss of amorphous chain at the interface. The influence of crystalline enthalpy, crystalline degree, lamellae thickness and interfacial energy on chain folding are studied. The results show that crystalline enthalpy reduces the probability of fold structure at large interfacial energy while almost no effect at small interfacial energy, indicating a synergistic effect between interfacial energy and crystalline enthalpy on the chain folding. It is also found that lamellae thickness promotes the fold structure while crystalline degree has an opposite effect. Our model demonstrates advantages in accurately describing the comprehensive features of polymer chain in polymer semi-crystal system and provided a semi-quantitative thermodynamic picture of chain folding in polymer crystallization. [Preview Abstract] |
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M1.00105: Exploring potential inhomogeneities induced by large deformation in polymer glasses Xiaoxiao Li, Yexin Zheng, Mesfin Tsige, Shi-Qing Wang Non-polymeric organic glasses rarely yield during external deformation. In contrast, polymeric glasses of high molecular weight can always undergo ductile deformation during which segmental mobility greatly increases [1]. We carried out molecular dynamics simulation based on a coarse-grained model [2] to investigate how polymeric glasses of high and low molecular weights respond differently to large deformation. In both uniaxial extension and simple shear, we observed inhomogeneous responses, e.g., spatially varying segmental mobility and strain localization. The presentation reports such inhomogeneities at different temperatures and rates for both long and short chain systems. [1] Bending, B.; Christison, K.; Ricci, J.; Ediger, M. Macromolecules 2014, 47, (2), 800-806. [2] Hsu, D. D.; Xia, W.; Arturo, S. G.; Keten, S. Macromolecules 2015, 48, (9), 3057-3068. [Preview Abstract] |
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M1.00106: Impact of melt-deformation on molecular structure and mechanical behavior of glassy polymers Jianning Liu, Xiaoxiao Li, Zhichen Zhao, Shi-Qing Wang This work studies effects of melt deformation such as extension and compression on mechanical behavior of glassy polymers. Depending on how the entanglement network is altered during melt deformation, mechanical properties of polystyrene and poly(methyl methacrylate) are changed at temperatures below Tg. Conversely, the observed mechanical behavior below Tg reveals how molecular structures at segmental levels have undergone distortion due to melt stretching or shear. This research expands well beyond our previous investigations that have demonstrated how and why melt-stretched PS and PMMA turns ductile at room temperature....$^{\mathrm{1}}$ and why a cold-drawn ductile polymer glass produces significant retractive stress upon annealing above the cold-drawing temperature..$^{\mathrm{2}}$ .1.Wang, S.-Q.; Cheng, S.; Lin, P.; Li, X. A phenomenological molecular model for yielding and brittle-ductile transition of polymer glasses. \textit{J. Chem. Phys. }\textbf{2014,} 141, (9), 094905. 2.Cheng, S.; Wang, S.-Q. Elastic Yielding after Cold Drawing of Ductile Polymer Glasses. \textit{Macromolecules }\textbf{2014,} 47, (11), 3661-3671. [Preview Abstract] |
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M1.00107: Changes of structure and properties in physical aging of polycarbonate Toshiaki Ougizawa, HIsashi Jufuku, Kai Hayashi Changes in amount of enthalpy relaxation and tensile properties with physical aging were measured in polycarbonate (PC) which is one of typical glassy polymer. PC annealed at the slightly lower temperature than $T_{\mathrm{g}}$ showed endothermic peak above $T_{\mathrm{g}}$ in DSC measurement and more brittle behavior in tensile measurements. And PC annealed at 30$^{\mathrm{o}}$C lower temperature than usual $T_{\mathrm{g}}$ showed 2 $T_{\mathrm{g}}$ and volume expansion in initial stage of annealing. After that the sample showed usual physical aging behavior as shown above. By contrast, it was found that the PC annealed at temperature (60$^{\mathrm{o}}$C or less) much lower than the $T_{\mathrm{g}}$ did not show those behaviors and new endothermic peak at temperature much lower than the $T_{\mathrm{g\thinspace }}$was observed. Based on these results, it was considered that the metastable structure, which was formed by annealing glassy polymer at temperature much lower than the$ T_{\mathrm{g}}$, suppresses the appearance of endothermic peak above $T_{\mathrm{g}}$ and the lowering of the mechanical properties by physical aging. [Preview Abstract] |
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M1.00108: Abstract Withdrawn
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M1.00109: Volume Recovery of Polymeric Glasses: Application of a Capacitance-based Measurement Technique Nazam Sakib, Sindee Simon Glasses, including polymeric glasses, are inherently non-equilibrium materials. As a consequence, the volume and enthalpy of a glass evolve towards equilibrium in a process termed structural recovery. Several open questions and new controversies remain unanswered in the field. Specifically, the presence of intermediate plateaus during isothermal structural recovery has been reported in recent enthalpy work. In addition, the dependence of the relaxation time on state variables and thermal history is unclear. Dilatometry is particularly useful for structural recovery studies because volume is an absolute quantity and volumetric measurements can be done in-situ. A capillary dilatometer, fitted with a linear variable differential transducer, was used previously to measure volume recovery of polymeric glass formers in our laboratory. To improve on the limitations associated with that methodology, including competition between the range of measurements versus the sensitivity, a capacitance-based technique has been developed following the work of Richert, 2010. The modification is performed by converting the glass capillary dilatometer into a cylindrical capacitor. For precision in capacitance data acquisition, an Andeen-Hagerling ultra-precision capacitance bridge (2550A, 1 kHz) is used. The setup will be tested by performing the signatures of structural recovery as described by Kovacs, 1963. Experiments are also planned to address the open questions in the field. [Preview Abstract] |
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M1.00110: Elastic yielding of melt-stretched glassy polymers below glass transition temperature Zhichen Zhao, Yexin Zheng, Mesfin Tsige, Shi-Qing Wang We have recently shown how effects of melt deformation on mechanical behavior of glassy polymers may be understood in terms of a molecular model [1], which can explain why melt-stretched polystyrene becomes completely ductile at room temperature. In our further investigation along this line, we uncovered a phenomenon that appears unknown in the literature. Mechanical tests reveal that melt-deformed PS and PMMA exhibit a sizable elastic retractive stress when annealed at temperatures that are still significantly below their glass transition temperatures. This work systematically investigates how characteristics of this elastic yielding, e.g., induction time and magnitude of the tensile stress, change as a function of the temperature at which melt stretching is carried out, the degree of melt stretching, the annealing temperature, composition of the glassy polymers, and aging history. [1]Wang, S. Q., Cheng, S., Lin, P., {\&} Li, X. (2014). A phenomenological molecular model for yielding and brittle-ductile transition of polymer glasses.The Journal of chemical physics,~141(9), 094905.. [Preview Abstract] |
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M1.00111: Solvent Size Dependent Structure Of Diblock Copolymer Micelles In N-alkane Sangho Lee, Tae-Young Heo, Soo-Hyung Choi Block copolymers can self-assemble into micelles in selective solvents. Theoretical description for the micelle structure is described the balance between core block stretching and core block-solvent interaction with the assumption that the core is melt state. So, core block was stretched and solvent entropy effect(e.g.solvent penetration into core)was simplified at the theoretical models. However, we observed PS-PEP micelle in squalane that the core block was nearly fully relaxed. In this study, we investigate the micelle structure as a function of solvent size. Here, we use Poly(styrene-b-ethylene-alt-propylene) in selective solvent such as n-alkanes. Solvents are favorable for PEP corona block and unfavorable PS core block. As solvent size decreases, solvent easily can penetrate into core, however, interaction parameter χ increases systematic. Critical micelle temperature(CMT) and detailed micelle structure were measured by Small-Angle X-ray Scattering. Interestingly, we observed that the CMT decreases as solvent size decreases. The core block is fully relaxed by comparing with core radius and 2 |
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M1.00112: Assembly and Conformation of PNIPAM and Molecular Analogs Below the LCST Xiaolong Lang, Michael J. A. Hore Poly(alkyl acrylamides), most notably poly(N-isopropylacrylamide) (PNIPAM), are widely studied thermoresponsive polymers. Linear PNIPAM, poly (N-n-propylacrylamide) (PNnPAM) and poly (N-cyclopropylacrylamide) (PNCPAM) were synthesized via RAFT polymerization to obtain polymers with varying end groups. The the polymers were studied with a combination of small-angle neutron scattering (SANS) and multi-angle (static) light scattering (MALS) to determine the influence of end group and monomer structure on assembly and conformation of the polymers in solution. Large scale clustering of the polymers is observed below the LCST, and as the terminal group became more hydrophobic, polymers formed micelles. These results are compared to 3- and 4-arm star-branched PNIPAM with similar end groups. The results indicate that, despite making up only a small fraction of the polymer, the terminal groups play a large role in both the conformation and assembly of PNIPAM and its analogs below the LCST. For star PNIPAM, changes to the structure of the polymer core led to distinct changes in the large scale clustering behavior of the polymer. [Preview Abstract] |
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M1.00113: Glassy dynamics of intermediate-chain-stiffness crystallizable polymer melts Hong Nguyen, Robert Hoy We contrast the dynamics in model unentangled polymer melts of chains of three different stiffnesses: flexible, intermediate, and rodlike. Flexible and rodlike chains, which readily solidify into close-packed crystals (respectively with randomly oriented and nematically aligned chains), display simple melt dynamics with Arrhenius temperature dependence and a discontinuous change upon solidification. Intermediate-stiffness chains, however, are fragile glass-formers displaying Vogel-Fulcher dynamical arrest, despite the fact that they also possess a nematic-close-packed crystalline ground state. No clear static-structural cause of this dynamical arrest is found. However, we find that the intermediate-stiffness chains display qualitatively different cooperative dynamics. Specifically, their stringlike motion (cooperative rearrangement) is correlated along chain backbones in a way not found for either flexible or rodlike chains. This activated "crawling" motion is clearly associated with the dynamical arrest observed in these systems, and illustrates one way in which factors controlling the crystallization vs. glass formation competition in polymers can depend nonmonotonically on chain stiffness. [Preview Abstract] |
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M1.00114: From Comb-like Polymers to Bottle-Brushes Heyi Liang, Zhen Cao, Andrey Dobrynin, Sergei Sheiko We use a combination of the coarse-grained molecular dynamics simulations and scaling analysis to study conformations of bottle-brushes and comb-like polymers in a melt. Our analysis show that bottle-brushes and comb-like polymers can be in four different conformation regimes depending on the number of monomers between grafted side chains and side chain degree of polymerization. In loosely-grafted comb regime (LC) the degree of polymerization between side chains is longer than side chain degree of polymerization, such that the side chains belonging to the same macromolecule do not overlap. Crossover to a new densely-grafted comb regime (DC) takes place when side chains begin to overlap reducing interpenetration of side chains belonging to different macromolecules. In these two regimes both side-chains and backbone behave as unperturbed linear chains with the effective Kuhn length of the backbone being close to that of linear chain. Further decrease spacer degree of polymerization results in crossover to loosely-grafted bottle-brush regime (LB). In this regime, the bottle-brush backbone is stretched while the side-chains still maintain ideal chain conformation. Finally, for even shorter spacer between grafted side chains, which corresponds to densely-grafted bottle-brush regime (DB), the backbone adopts a fully extended chain conformation, and side-chains begin to stretch to maintain a constant monomer density. [Preview Abstract] |
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M1.00115: Gluing Gels by Soft Nanoparticles Ryan Sayko, Zhen Cao, Heyi Liang, Andrey Dobrynin Nanoparticles have been recently shown to act as effective adhesives between two soft materials. Using a combination of theoretical calculations and molecular dynamics simulations, we investigated the contact mechanics of a soft nanoparticle at the interface of two gel-like surfaces. Depending on the nanoparticle size and the elastic modulus of nanoparticle and gels, the reinforced interface could be in a bridging or Pickering state. The equilibrium radius of contact, and the deformations of nanoparticle and gels are controlled by a dimensionless parameter - elastocapillary number, describing both adhesive and wetting regimes. We calculated the potential of mean force between the equilibrium contact state and the separated state using the Weighted Histogram Analysis Method. Simulation results show that soft nanoparticles could achieve a larger work of separation compared with a rigid nanoparticle. [Preview Abstract] |
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M1.00116: Dynamics of Bottlebrush Networks Zhen Cao, William Daniel, Mohammad Vatankhah-Varnosfaderani, Sergei Sheiko, Andrey Dobrynin The deformation dynamics of bottlebrush networks in a melt state is studied using a combination of theoretical, computational, and experimental techniques. Three main molecular relaxation processes are identified in these systems: (i) relaxation of the side chains, (ii) relaxation of the bottlebrush backbones on length scales shorter than the bottlebrush Kuhn length ($b_{\mathrm{K}})$, and (iii) relaxation of the bottlebrush network strands between cross-links. The relaxation of side chains having a degree of polymerization (DP),~$n_{\mathrm{sc}}$, dominates the network dynamics on the time scales $\tau_{\mathrm{0}}$~\textless ~$t$~$\le \quad \tau _{\mathrm{sc}}$, where $\tau_{\mathrm{0}}$~and $\tau _{\mathrm{sc}}$~$\approx \quad \tau_{\mathrm{0}}(n_{\mathrm{sc}}$~$+$ 1)$^{\mathrm{2}}$~are the characteristic relaxation times of monomeric units and side chains, respectively. In this time interval, the shear modulus at small deformations decays with time as~$G_{\mathrm{0}}^{\mathrm{BB}}(t) \quad \sim $~$t^{\mathrm{-1/2}}$. On time scales~$t$~\textgreater $\tau_{\mathrm{sc}}$, bottlebrush elastomers behave as networks of filaments with a shear modulus~$G_{\mathrm{0}}^{\mathrm{BB}}(t) \quad \sim $ ($n_{\mathrm{sc}}$~$+$ 1)$^{\mathrm{-1/4}}t^{\mathrm{-1/2}}$. Finally, the response of the bottlebrush networks becomes time independent at times scales longer than the Rouse time of the bottlebrush network strands. In this time interval, the network shear modulus depends on the network molecular parameters as~$G_{\mathrm{0}}^{\mathrm{BB}}(t) \quad \sim $ ($n_{\mathrm{sc}}$~$+$ 1)$^{\mathrm{-1}}N^{\mathrm{-1}}$. Analysis of the simulation data shows that the stress evolution in the bottlebrush networks during constant strain-rate deformation can be described by a universal function. [Preview Abstract] |
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M1.00117: Control of polymer network topology in semi-batch systems Rui Wang, Bradley Olsen, Jeremiah Johnson Polymer networks invariably possess topological defects: loops of different orders. Since small loops (primary loops and secondary loops) both lower the modulus of network and lead to stress concentration that causes material failure at low deformation, it is desirable to greatly reduce the loop fraction. We have shown that achieving loop fraction close to zero is extremely difficult in the batch process due to the slow decay of loop fraction with the polymer concentration and chain length. Here, we develop a modified kinetic graph theory that can model network formation reactions in semi-batch systems. We demonstrate that the loop fraction is not sensitive to the feeding policy if the reaction volume maintains constant during the network formation. However, if we initially put concentrated solution of small junction molecules in the reactor and continuously adding polymer solutions, the fractions of both primary loop and higher-order loops will be significantly reduced. There is a limiting value (nonzero) of loop fraction that can be achieved in the semi-batch system in condition of extremely slow feeding rate. This minimum loop fraction only depends on a single dimensionless variable, the product of concentration and with single chain pervaded volume, and defines an operating zone in which the loop fraction of polymer networks can be controlled through adjusting the feeding rate of the semi-batch process. [Preview Abstract] |
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M1.00118: Effects of the Number of Hydrogen Bonds on Mechanical Properties of Block Copolymer-Based Supramolecular Elastomers Atsushi Noro, Takato Kajita, Yushu Matsushita A series of polystyrene-b-[poly(butyl acrylate)-co-polyacrylamide]-b-polystyrene triblock copolymers with almost the same molecular weight but with various mole fractions of acrylamide units was prepared. Tensile tests revealed that the larger maximum tensile stress was attained when the triblock copolymer had the larger fraction of acrylamide units in a melt middle block. This is because the effective cross-link density in the sample is larger. But further increase of acrylamide units in the melt middle block caused decrease of the breaking elongation. This is because stress concentration at glassy domains by elongation easily occurs when the number of hydrogen bonds incorporated into the melt middle block is large. [Preview Abstract] |
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M1.00119: Surface instabilities of elastic bilayers with patterned stiff films Tetsu Ouchi, Ryan Hayward Wrinkles and creases represent two fundamental modes of elastic instability for surfaces under compression. Wrinkles usually form on bilayers of a stiff film on a soft foundation, while creases usually form on the surface of a single soft layer. Although both modes have been widely studied on their own, the interplay between these two phenomena for bilayers with patterned stiff films is poorly understood. Here, we fabricated laterally-patterned films of stiff material laminated on an elastomer substrate, and analyzed the effects of the pattern geometries on surface instability modes. We have characterized the formation and propagation of wrinkles on `islands' of the stiff film, as well as the formation of creases at the edges of islands and in-between neighboring islands. At sufficiently high strains, neighboring islands may come into contact, and wrinkle troughs may also serve as nucleation sites for formation of creases that channel across the elastomer surface. [Preview Abstract] |
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M1.00120: Abstract Withdrawn
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M1.00121: Charge Transport and Ion Dynamics in Copolymers Containing Ammonium-based Polymerized Ionic Liquids Matthew Harris, Maximilian Heres, Veronika Strehmel, Roberto Benson, Joshua Sangoro Charge transport is investigated in copolymers containing polymerized ionic liquids (polyIL) using broadband dielectric spectroscopy. The lowest volume fraction polyIL copolymer studied exhibits interfacial polarization at the polyIL/PMMA phase boundary. At the intermediate volume fraction, ionic diffusion rates are identical to those of the polyIL homopolymer but ionic conductivity is lower due to a reduction in the number density of mobile charge carriers. The highest polyIL volume fraction studied showed enhanced conductivity over the PIL homopolymer due to improved ion dissociation, evidenced by increased static permittivity. We demonstrate that ion transport can be enhanced in a PIL block copolymer system by incorporating a non-conducting phase and conclude that the conductivities of the PIL copolymers are significantly altered by varying the volume fraction. [Preview Abstract] |
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M1.00122: Interaction and Anomalous Diffusion of Polyelectrolytes in Polyzwitterionic Complexes. Kehua Lin, Benxin Jing, Yingxi Zhu Oppositely charged polyelectrolytes can associate in aqueous solution form distinct condensed phase such as liquid-like coacervates and solid/gel-like complexes. While a great deal is known about their phase behaviors, the interaction and structural dynamics of polyelectrolyte complexes remain unclear. Use zwitterionic polymer, poly (sulfobetaine methacrylate) (PSBMA), we compare its interaction and complex formation with polycation, poly(2-vinylpyridine) (P2VP) and polyanion, poly(styrene sulfonate) (PSS) in aqueous solution. We observe the formation of biphasic PSBMA-P2VP coacervates at low salt, in sharp contrast to the formation of PSBMA-PSS gel at the same solution condition, given that PSBMA is net negatively charged in the salted solution. To examine the interplay between polyelectrolyte interaction and structural dynamic of polyelectrolyte complexes, we investigate the self-diffusion of single P2VP and PSS in PSBMA-based complexes by fluorescence correlation spectroscopy and fluorescence recovery after photobleaching. Fickian diffusion behavior is observed with PSS in PSBMA-PSS gel. However, fast and slow diffusion modes are observed in the dense PSBMA-P2VP coacervate after the removal of supernatant, suggesting inhomogeous structure of dense coacervates. Fickian diffusion of P2VP in PSBMA-P2VP coacervates could be recovered at high salt. A simple model is proposed to describe the impact of competing electrostatic and entropic forces on the dynamic heterogeneity in macroscopically homogenous polyzwitterionic complexes. [Preview Abstract] |
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M1.00123: A Cation-containing Polymer Anion Exchange Membrane based on Poly(norbornene) Frederick Beyer, Samuel Price, Xiaoming Ren, Alice Savage Cation-containing polymers are being studied widely for use as anion exchange membranes (AEMs) in alkaline fuel cells (AFCs) because AEMs offer a number of potential benefits including allowing a solid state device and elimination of the carbonate poisoning problem. The successful AEM will combine high performance from several orthogonal properties, having robust mechanical strength even when wet, high hydroxide conductivity, and the high chemical stability required for long device lifetimes. In this study, we have synthesized a model cationic polymer that combines three of the key advantages of Nafion. The polymer backbone based on semicrystalline atactic poly(norbornene) offers good mechanical properties. A flexible, ether-based tether between the backbone and fixed cation charged species (quaternary ammonium) should provide the low-Tg, hydrophilic environment required to facilitate OH- transport. Finally, methyl groups have been added at the beta position relative to the quaternary ammonium cation to prevent Hoffman elimination, one mechanism by which AEMs are neutralized in a high pH environment. In this poster, we will present our findings on mechanical properties, morphology, charge transport, and chemical stability of this material. [Preview Abstract] |
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M1.00124: Single-ion conducting diblock terpolymers for lithium-ion batteries Melody Morris, Thomas H. Epps, III Block polymer (BP) electrolytes provide an attractive route to overcome the competing constraints of high conductivity and mechanical/thermal stability in lithium-ion batteries through nanoscale self-assembly. For example, macromolecules can be engineered such that one domain conducts lithium ions and the other prevents lithium dendrite formation. Herein, we report on the behavior of a single-ion conducting BP electrolyte that was designed to facilitate the transport of lithium ions. These polymers differ from traditional salt-doped BP electrolytes, which require the addition of a lithium salt to bestow conductivity and typically suffer from substantial counterion motion that reduces efficiency. New single-ion BPs were synthesized, and the nanoscale morphologies were determined using small angle X-ray scattering and transmission electron microscopy. Electrolyte performance was measured using AC impedance spectroscopy and DC polarization, and the results were correlated to nanoscale morphology and ion content. Enhanced physical understanding of single-ion BPs was gained by connecting the ion mobility to the chemistry, chain structure, and ion content of the single-ion BP. These studies can be applied to other charged-neutral block polymers to elucidate the effects of ion content on self-assembly and macroscopic properties. [Preview Abstract] |
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M1.00125: Laponite concentration optimized for the thermoresponsive gelation of PEG-rich PLGA-PEG-PLGA/laponite solution Keishi Tanimoto, Tomoki Maeda, Atsushi Hotta The aqueous solution of poly (D,L-lactic acid-co-glycolic acid)-b-poly (ethylene glycol)-b-poly (D,L-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) changes from sol to gel states by increasing temperature. Considering the biomedical use of PLGA-PEG-PLGA as e.g. an injectable drug delivery material, lowering the solute concentration of the hydrogel with a lower molecular weight of the PLGA block is highly significant. Our group has recently developed a high water-content hydrogel composed of laponite, an inorganic nanoparticle and PLGA-PEG-PLGA with a relatively small PLGA block (PLGA-PEG-PLGA of 800-1500-800) at the solute concentration of 3.9 weight percent. In this study, the laponite concentration was optimized for the synthesized PLGA-PEG-PLGA with different molecular weights of PLGA ranging from 250 g/mol to 1900 g/mol. The molecular weight of PEG was fixed at 1500 g/mol. It was found that as the molecular weight of PLGA decreased from 1900 g/mol to 250 g/mol, the laponite concentration required for the thermoresponsive gelation of aqueous PLGA-PEG-PLGA/laponite solution slightly increased to 1.25 weight percent [Preview Abstract] |
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M1.00126: Controlling the biodegradability of poly(butylene succinate-co-butylene adipate) (PBSA) by solvents used in the dried-gel process Hana Yamazaki, Saya Kamitabira, Tomoki Maeda, Atsushi Hotta Considering an environmentally friendly material, poly(butylene succinate-co-butylene adipate)(PBSA) is one of the attractive biodegradable plastics that can be eventually degraded into H$_{\mathrm{2}}$O and CO$_{\mathrm{2}}$ by neighboring water molecules and microorganisms after the disposal. In order to expand the application of PBSA, the precise control of the biodegradability of PBSA is necessary. In this study, the dried-gel process was introduced to control the biodegradability of PBSA. The dried PBSA gels were prepared by using three different solvents (toluene, cyclohexanone, and o-dichlorobenzene). The scanning electron microscopy (SEM) micrographs revealed that the PBSA prepared by toluene had smaller spherocrystals than the other PBSA dried-gels prepared by cyclohexanone or o-dichlorobenzene. The biodegradability testing by immersing the three types of PBSA in NaOH aq. showed that the percentage of the weight loss of the PBSA produced by toluene was the highest. The results indicated that the microstructures of PBSA could be controlled by changing solvents during the gel preparations, and that the biodegradability of PBSA could therefore be efficiently modified by changing solvents. [Preview Abstract] |
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M1.00127: Impact of Helical Polypeptoid Polymer Chain Shape on Block Copolymer Self-Assembly Emily Davidson, Adrianne Rosales, Anastasia Patterson, Ronald Zuckermann, Rachel Segalman Polypeptoid chain shape is tunable across a range of degrees of helicity via the introduction and sequence of bulky, chiral side chains; as the polypeptoid chain's degree of helicity is increased, the chain stiffness increases. This work shows that these effects are translated to bulk self-assembly where increases in chain stiffness for chemically identical materials on the monomer level drives increases in the diblock domain spacing. By selectively placing the helical part of the peptoid adjacent to or far from the block junction, we show that the stabilized peptoid helix distant from the block junction results in a significantly greater degree of overall domain stretching. Furthermore, a diblock with a helical polypeptoid block displays a higher order-disorder transition relative to the diblock with the chemically analogous but disordered block. [Preview Abstract] |
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M1.00128: The Effect of Tunable Surface Energy Interlayers on the Control of Phase Behavior and Orientation of Block Copolymers in 2D Confinement Youngkeol Kim, Sungyoul Hwang, Kookheon Char There have been many studies to investigate the phase behavior of block copolymers (BCPs) in cylindrical confinement. In the nanometer scale 2D confinement, the phase behavior of BCPs is mainly dependent upon the commensurability of BCPs within confinement and interfacial interaction. However, most studies have focused only on the effects of commensurability on the microdomains of BCP. In this study, we employed organosilicates (OS) which have surface energy, tunable by curing temperature, as interlayers to examine the phase behavior and orientation of BCPs. The OS interlayer was coated on the inner surface of anodized aluminum oxide (AAO) pores by template-wetting method and cured in a range of temperature to control the surface energy of the interlayers. Lamellae-forming poly(styrene-$b$-methyl methacrylate) (PS-b-PMMA) (SMA) was infused into the OS-coated AAO pores by capillary forces. With the detailed analysis, we could identify that the self-assembly of SMA within 2D confinement is influenced by competing entropic and enthalpic effects as the interfacial energy is varied. By simply controlling the curing temperature of the OS interlayer, various morphologies and orientations arising from both the preferential and neutral wetting were identified. [Preview Abstract] |
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M1.00129: Effects of Morphology on Dynamics of Block Copolymer Systems Kuan-Hsuan Shen, Lisa Hall It is well known that block copolymers can microphase separate into ordered structures such as lamellae, hexagonally packed cylinders, or the bicontinuous double gyroid phase. Understanding the dynamics of the chains themselves and of added selective small molecule penetrants is relevant to the design of polymeric systems for transport applications. We expect that chain and penetrant dynamics are strongly dependent on morphology, while chain dynamics are also significantly impacted by individual polymer conformations within the morphology. For instance, in prior work on tapered polymers with a midblock of various concentration profiles, chains that fold back and forth across the lamellar interface were shown to have significantly decreased diffusion. Here we use coarse-grained molecular dynamics simulations to study how chain and penetrant dynamics depend on domain spacing, polymer conformations, and microphase morphology. We initialize systems of various fractions of A monomers in lamellar, cylinder, or gyroid microphases by growing polymers in a constrained random walk such that the two blocks are placed on opposite sides of the interface. We include, for comparison, systems with the same fraction of A that are initialized (and kinetically trapped) in different microphases, and show how this impacts polymer relaxation. How the dependence of penetrant diffusion on morphology relates to that of polymer chains will also be discussed. [Preview Abstract] |
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M1.00130: Gyroid structure via highly asymmetric ABC and AB blends Seonghyeon Ahn, Jongheon Kwak, Chungryong Choi, Jin Kon Kim Gyroid structures are very important because of their co-continuous and network structures. However, a block copolymer shows gyroid structures only at ~35$\%$ volume fraction of one block. In this study, we designed ABC/AB blend system. B (polystyrene (PS)) is the matrix, while A (polyisoprene (PI)) and C (poly(2-vinyl pridine (P2VP)) are the core part. This blend shows gyroid structures at 20$\%$ volume fraction, that is smaller than that observed at diblock copolymer. Morphologies of neat block copolymers and blends were characterized by TEM and small angle X-ray scattering. [Preview Abstract] |
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M1.00131: Synthesis and kinetics studies of poly(styrene-b-vinylmethylsiloxane) and its thin film ordering by thermal and solvent annealing Sourav Chatterjee, Md Fakar Uddin, Baraka Lwoya, Julie N.L. Albert Nano-structured thin film materials are important materials that find uses in templating and membrane applications. Block copolymers (BCP) have gained considerable attention for next-generation lithographic masks due to their self-assemble into morphologies with periodic sub 20 nm feature sizes with high regularity and reproducibility. A novel synthetic block copolymer of poly(styrene-b-vinylmethylsiloxane) (PS-b-PVMS) was synthesized. Like poly(styrene-b-dimethylsiloxane), this polymer has a high Flory Huggins interaction parameter between blocks to minimize feature size. Furthermore, incorporation of the vinyl side group provides an opportunity for post-polymerization chemical modification to manipulate the interaction parameter or impart functionality for various applications. Synthesis and kinetic studies of PS-b-PVMS as well as PS and PVMS homopolymers will be presented. All polymers are well characterized by proton NMR and GPC. As proof of concept, we show that block copolymers having different block fractions self-assemble into the expected nanostructures (lamellae, cylinders, spheres). Thin film studies also will be presented showing how the ordering of PS-b-PVMS is affected by different solvent and thermal annealing conditions. [Preview Abstract] |
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M1.00132: Thermodynamic Interactions in Model Polyolefin/Polydiene Blends Jialin Qiu, Katrina Mongcopa, Ruixuan Han, Carlos López-Barrón, Megan Robertson, Ramanan Krishnamoorti The Flory-Huggins interaction parameter $\chi$ is used to describe the interactions between polymers and is of crucial importance in determining the processing conditions for polymer mixtures and block copolymers. The temperature dependence of $\chi$ between 1,2-polybutadiene and saturated 1,2-polybutadiene was investigated. 1,2-Polybutadiene was synthesized by anionic polymerization with 1,2-dipiperidinoethane as an additive to achieve high vinyl content (99.0\%). The synthesized 1,2-polybutadiene was saturated with deuterium to provide contrast for small-angle neutron scattering (SANS) experiments. Two series of blends were prepared with differing molecular weight. Values of $\chi$ were extracted from fitting the Random Phase Approximation (RPA) to SANS data. Additionally, $\chi$ was extracted from Zimm analysis, using the low-angle scattering intensity. $\chi$ extracted by RPA and Zimm analyses were in good agreement. The temperature dependencies of $\chi$ characterized for two separate blends of differing molecular weight were consistent with one another. The large $\chi$ parameter observed in this system indicates strong repulsion in blends of polydienes and polyolefins. [Preview Abstract] |
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M1.00133: Study of Self-Assembly in Block Copolymer (BCP)-Homopolymer Blends using Dissipative Particle Dynamics (DPD) Simulations Amy Goodson, Md Fakar Uddin, Julie Albert We demonstrate the use of Dissipative Particle Dynamics (DPD) simulations to study self-assembly behavior of block copolymer (BCP) melts and BCP-homopolymer blends. DPD is a coarse-grained simulation technique that preserves hydrodynamics, thereby allowing simulations to capture not only equilibrium conformations but also understand the pathways by which they form. DPD simulations of pure A-block-B melts conducted at varying f and chi*N produce a phase diagram that mimics the trends seen experimentally and in Self-Consistent Field Theory (SCFT). These simulations also reproduce expected domain spacing relationships with chi*N. DPD simulations of BCP-homopolymer blends match results obtained experimentally in our group. As homopolymer is added to a symmetric BCP, lamellar domain spacing swells. At a critical homopolymer content, the lamellar structure is lost and a non-symmetric, bicontinous microstructure forms. We also examine the relationship of block and homopolymer molecular weights and the microstructure observed in the blend. [Preview Abstract] |
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M1.00134: Thin film Phase behavior and domain spacing of binary and ternary homopolymer/block copolymer (BCP) blends. Md Fakar Uddin, Baraka S. Lwoya, Amy Goodson, Amira Muhsen, Julie N.L. Albert The phase behavior of binary and ternary blends composed of poly(styrene-$b$-dimethylsiloxane) (PS-$b$-PDMS) and corresponding homopolymers of polystyrene (PS) and polydimethylsiloxane (PDMS) in thin films was investigated using atomic force microscopy(AFM). Films were cast on preferential surfaces that led to parallel orientation upon thermal annealing. AFM height images revealed the formation of islands or holes at the surface of the films from which the domain spacing was determined. The addition of PS to PS-$b$-PDMS changes the composition, which results in domain swelling as well as a shift in nano/microstructure in binary blends. For ternary blends, incorporation of PS and PDMS in the BCP system is done such that the overall composition of the blends remains the same as the pristine PS-$b$-PDMS. Again, domain spacing increased with increasing homopolymer addition; because the lamellar nano/microstructure was retained, a shift from holes to islands was observed for constant film thickness. Additionally, as long as the thin film blends retain morphological integrity, the theoretical and experimental surface coverage of island/hole features showed good agreement for both binary and ternary blend systems. [Preview Abstract] |
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M1.00135: Molecular Dynamics Simulation on Rheological and Dyanmics Properties of Dynamically Asymmetric Binary Polymer Blends Wei Peng, Rahmi Ozisik, Pawel Keblinski The rheological and dynamic properties of dynamically asymmetric binary polymer blends are studied via Molecular Dynamics simulations. The current study is inspired by Senses et al. (Senses, E.; Isherwood, A.; Akcora, P. ACS Appl. Mater. Interfaces 2015, 7, 14682), where a reversible thermal stiffening behavior was observed in a nanocomposite, in which the matrix chains and surfactant polymer chains on the nanofillers showed 200 ºC difference in their glass transition temperatures (Tgs). In this work, we studied the rheological and dynamic properties of a blend system with two distinct blend morphologies: a well-mixed blend and a phase separated blend, representing dynamically coupled and dynamically confined states, respectively. The blend systems are made up of two types of bead-spring model chains with a large glass transition difference. Simulation results showed that the mixed systems were drastically stiffer than the unmixed ones -- the storage modulus of the mixed blend was almost an order of magnitude greater than that of the neat matrix polymer. The effects of various parameters such as chain length and volume fraction of high-Tg chains on various static, dynamic and viscoelastic properties were further investigated to explore the mechanism of the stiffening. [Preview Abstract] |
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M1.00136: Fluoropolymer based composite with Ag particles as 3D printable conductive ink for stretchable electronics Amit Kumar, Thanh Giang La, Xinda Li, Hyun Joong Chung The recent development of stretchable electronics expands the scope of wearable and healthcare applications. This creates a high demand in stretchy conductor that can maintain conductivity at high strain conditions. Here, we describe a simple fabrication pathway to achieve stretchable, 3D-printable and low-cost conductive composite ink. The ink is used to print complex stretchable patterns with high conductivity. The elastic ink is composed of silver(Ag) flakes, fluorine rubber, an organic solvent and surfactant. The surfactant plays multiple roles in in the composite. The surfactant promotes compatibility between silver flakes and fluorine rubber; at the same time, it affects the mechanical properties of the hosting fluoropolymers and adhesion properties of the composite. Based on experimental observations, we discuss the exact role of the surfactant in the composite. The resulting composite exhibits high conductivity value of 8.49 *10 $^{\mathrm{4}}$ S/m along with high reliability against repeated stretching/releasing cycles. Interesting examples of transfer printing of the printed ink and its applications in working devices, such as RFID tag and antennas, are also showcased. [Preview Abstract] |
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M1.00137: Fabrication of the stereocomplex polylactide nanofibers for the improvement of the thermomechanical properties of poly(L-lactide) Naruki Kurokawa, Atsushi Hotta Stereocomplex polylactide (sc-PLA) crystals can be generated through the mixture of enantiomeric polylactides, presenting high mechanical properties and high thermal resistance. In this study, sc-PLA was electrospun into nanofibers and compounded into poly(L-lactide) (PLLA) to improve the thermomechanical properties of PLLA. The synthesis condition of the sc-PLA nanofibers was optimized by adjusting the conductivity of the dichloromethane (DCM) solvent by adding pyridine. The sc-PLA nanofibers with the average diameter of 367 nm were successfully fabricated by selecting the solvent composition of DCM : pyridine $=$ 7 : 3 with the sc-PLA concentration of 7 weight percent. By measuring the conductivity, it was found that the conductivity of the mixed solvents of DCM : pyridine $=$7 : 3 was the highest, which was, in fact, 81.4 times higher than that of pure DCM. The fine sc-PLA nanofibers were compounded into PLLA by compression molding. The storage modulus of sc-PLA/PLLA was 21.8 times higher than that of pure PLLA at the fiber concentration of 15 weight percent. The sc-PLA nanofibers were found to be useful as a reinforcement material for PLLA to improve the thermomechanical properties. [Preview Abstract] |
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M1.00138: Active microrheology of entangled biopolymer composites link polymer flexibility and length to molecular force response Robert Fitzpatrick, Cole Hauer, Carl Kyrillos, Ryan McGorty, Rae Robertson-Anderson Entangled polymers have complex viscoelastic properties that are tuned by polymer lengths and flexibilities. Entangled composites of distinct polymers offer added versatility and display nonlinear mechanics, serving as a platform for multifunctional materials. To determine the role of flexibility and length in polymer composites we use optical tweezers and confocal microscopy to measure mechanical and structural properties of co-entangled actin and DNA. Actin filaments have lengths of 5-20 $\mu$m, comparable to their persistence length, while DNA of similar lengths have hundreds of persistence lengths per chain. To characterize the nonlinear mechanics of actin-DNA composites, we optically drive a microsphere through the composite and measure the induced force during and following strain. We characterize viscoelasticity and relaxation timescales; and determine the dependence of these quantities on the actin:DNA ratio (0:1-1:0) and DNA length (4-100 $\mu$m). We use confocal microscopy to image distinctly–labeled co-entangled actin and DNA and characterize network homogeneity and fluctuations. Initial results show actin and DNA are well-integrated and form structurally homogenous networks that exhibit stiffness and relaxation times that increase nonlinearly with increased actin. [Preview Abstract] |
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M1.00139: On PVDF-Carbon Nanotubes Composites Chamath Dannagoda, Maxim Sumets, Karen Martirosyan, Heinrich Foltz, Mircea Chipara Carbon Nanostructures (Vapor Grown Carbon Nanofibers and Single Walled Carbon Nanotubes; CN) have been dispersed within polyvinylidene fluoride (PVDF) by melt mixing, using a three steps program (mixing at 190 ~C for 60 rpm and 30 minutes, at 210 ~ C for 80 rpm and 15 minutes, and at 180 ~C and 60 rpm for 30 minutes.) The mixing was set at a relatively high temperature as the melting temperature of PVDF is about 177 $^{\mathrm{o}}$C. The as obtained composites were hot pressed into small discs with a diameter of 1 cm and a thickness of about 1 mm. Raman investigations on these samples have been done before the deposition of the electrical contacts. The temperature and frequency dependence of the electrical properties of these nanocomposites was measured. The details regarding the electrical conduction mechanisms are reported. The effect of the CN concentration and aspect ratio on the electrical properties is analyzed within the percolation theory. Additional DSC data was used to analyze glass, melting, and crystallization temperatures and their effect on charge transport. [Preview Abstract] |
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M1.00140: PEO-C60 NanocompositesComposites Roberto Rangel, Dorina Chipara, Hilario Cortez, Edgar Munoz, Mircea Chipara The effect of the nature of dispersion fluid (solvent or non-solvent) on the physical properties and structure of nanocomposites obtained by dispersing C60 within a high molecular weight polyethylene oxide (PEO)-was investigated in detail by Raman spectroscopy, Wide Angle X-Ray Scattering, Differential Scanning Calorimetry, and thermogravimetric analysis. Optical and electron microscopy were used to assess the dispersion of the nanofiller. The fluid component was selected to be a solvent for the polymeric matrix. However, the fluids were selected to be non-solvent (water) or solvents (chlorophorm, toluene) for the nanofiller. In all cases, the mixtures or solutions fluid $+$nanofiller$+$polymer were stirred 1 hour, sonicated 30 minutes, and then left in an oven at 110$^{\mathrm{o}}$C for 12 h to fully remove the solvent. The as obtained solid nanocomposites were further tested. TGA has been used to confirm solvent evaporation. The study aims at a better understanding of the role of the nanofiller solubility in the dispersion of nanomaterials within polymeric matrices. [Preview Abstract] |
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M1.00141: Gibbs Ensemble Simulations of the Solvent Swelling of Polymer Films Thomas Gartner, Thomas Epps, III, Arthi Jayaraman Solvent vapor annealing (SVA) is a useful technique to tune the morphology of block polymer, polymer blend, and polymer nanocomposite films. Despite SVA's utility, standardized SVA protocols have not been established, partly due to a lack of fundamental knowledge regarding the interplay between the polymer(s), solvent, substrate, and free-surface during solvent annealing and evaporation. An understanding of how to tune polymer film properties in a controllable manner through SVA processes is needed. Herein, the thermodynamic implications of the presence of solvent in the swollen polymer film is explored through two alternative Gibbs ensemble simulation methods that we have developed and extended: Gibbs ensemble molecular dynamics (GEMD) and hybrid Monte Carlo (MC)/molecular dynamics (MD). In this poster, we will describe these simulation methods and demonstrate their application to polystyrene films swollen by toluene and $n$-hexane. Polymer film swelling experiments, Gibbs ensemble molecular simulations, and polymer reference interaction site model (PRISM) theory are combined to calculate an effective Flory-Huggins $\chi $ ($\chi_{eff})$ for polymer-solvent mixtures. The effects of solvent chemistry, solvent content, polymer molecular weight, and polymer architecture on $\chi_{eff}$ are examined, providing a platform to control and understand the thermodynamics of polymer film swelling. [Preview Abstract] |
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M1.00142: Thin film self-assembly of PVMS-b-PMMA block copolymer Baraka Lwoya, Md Uddin, Sourav Chatterjee, Julie Albert Self-assembly of block copolymers has been explored for numerous years with a primary emphasis on nanolithographic templates and membrane applications. Block copolymers (BCPs) hold great promise as next-generation patterning materials for sub-10 nm nano-electronic applications. However, the inherent properties to develop smaller more ordered thin films (\textasciitilde 10-100 nm) is greatly hindered by the inability of the low segregation strength of conventional polymers such as poly(styrene-\textit{block}-methylmethacrylate). We aim at addressing this issue by firstly synthesizing strongly segregating BCPs of poly(vinylmethylsiloxane-\textit{block}-methyl methacrylate) (PVMS-$b-$PMMA) with different block volume fractions. Second, we induce self-assembly by either thermal or solvent annealing and characterize the morphology by atomic force microscopy (AFM). In addition, the use of a block with a pendant vinyl group provides the ability to functionalize the PVMS segment by thiol-ene reaction, either to further control of the segregation strength or to impart desirable surface chemical properties (e.g., adhesion/lift-off in templating or functionality in membranes). [Preview Abstract] |
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M1.00143: Direct visualization of nanoparticle dynamics at liquid interfaces Yige Gao, Paul Kim, David Hoagland, Tom Russell Ionic liquids, because of their negligible vapor pressures and moderate viscosities, are suitable media to investigate the dynamics of different types of dispersed nanoparticles by scanning electron microscopy. No liquid cell is necessary. Here, Brownian motions of nanoparticles partially wetted at the vacuum-liquid interface are visualized by low voltage SEM under conditions that allow single particle tracking for tens-of-minutes or longer. Conductive, nonconductive, semiconductive, and core-shell conductive-nonconductive nanoparticles have all been studied, and their interactions with each other in one- and two-component layers, as manifested in particle trajectories, differ significantly. For example, Au-coated silica nanoparticles aggregate above a threshold current, whereas aggregated silica-coated Au nanoparticles disaggregate at the same conditions. The impacts of surface concentration of nanoparticle dynamics were observed for one-component and two-component layers, with both global and localized motions visualized for single particles even in dense environments. As the surface concentration increases, the diffusion coefficient drops, and when the concentration reaches a critical threshold, the nanoparticles are essentially frozen. [Preview Abstract] |
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M1.00144: SOFT CONDENSED MATTER |
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M1.00145: Impact of projectiles of different geometries on dry granular media using DEM simulations Spandana Vajrala, Hosain Bagheri, Heather Emady, Hamid Marvi Recently, several studies involving numerical and experimental methods have focused on the study of impact dynamics in both dry and wet granular media. Most of these studies considered the impact of spherical projectiles under different conditions, while representative models could involve more complex shapes. Examples include such things as an animal’s foot impacting sand or an asteroid hitting the ground. Dropping different shaped geometries with conserved density, volume and velocity on a granular bed may experience contrasting drag forces upon penetration. This is the result of the difference in the surface areas coming in contact with the granular media. Therefore, this work will utilize three-dimensional Discrete Element Modelling (DEM) simulations to observe and compare the impact of different geometries like cylinder and cuboid of same material properties and volume. These geometries will be impacted on a loosely packed non-cohesive dry granular bed with the same impact velocities where the effect of surface area in contact with the granular media will be analyzed upon impact and penetration. [Preview Abstract] |
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M1.00146: Simulation of active polygons in 2 dimensions. Robert Martin, Johannes Zwanikken Many phases of matter are being studied in the field of Soft Matter beyond the standard categories of gas, liquid and solid. The rules that govern these phases are often well understood in thermal equilibrium, but do not apply to dissipative or active systems of self-propelled particles. We study the dynamics of 2-dimensional active polygons by means of simulation techniques, to characterize the formation of structure and substructures in driven ensembles, and search for a theoretical framework that relates these phases to the dynamical properties of the particles. [Preview Abstract] |
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M1.00147: The rheology and microstructure of aging thermoreversible colloidal gels {\&} attractive driven glasses Norman Wagner, Melissa Gordon, Christopher Kloxin The properties of colloidal gels and glasses are known to change with age, but the particle-level mechanisms by which aging occurs is are fully understood, which limits our ability to predict macroscopic behavior in these systems. In this work, we quantitatively relate rheological aging to structural aging of a model, homogenous gel and attractive driven glass by simultaneously measuring the bulk properties and gel microstructure using rheometry and small angle neutron scattering (Rheo-SANS), respectively. Specifically, we develop a quantitative and predictive relationship between the macroscopic properties and the underlying microstructure ($i.e.,$ the effective strength of attraction) of an aging colloidal gel and attractive driven glass and study it as a function of the thermal and shear history. Analysis with mode coupling theory is consistent with local particle rearrangements as the mechanism of aging, which lead to monotonically increasing interaction strengths in a continuously evolving material and strongly supports aging as a trajectory in the free energy landscape dominated by local particle relaxations. The analyses and conclusions of this study may be 1) industrially relevant to products that age on commercial timescales, such as paints and pharmaceuticals, 2) applicable to other dynamically arrested systems, such as metallic glasses, and 3) used in the design of new materials. [Preview Abstract] |
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M1.00148: The diffusion and the size of a knot in a polymer with side chains Liang Dai, Patrick Doyle Knots can occur in biopolymers, e.g. DNA and peptides, and synthetic polymers. Polymers often have side chains. We perform Brownian dynamics simulations to investigate the effects of side chains on the diffusion and the size of a knot on a stretched polymer. Three parameters in our model control knots: the length of side chains $L_{side}$, the gap between two adjacent side chains $L_{gap}$, and the stretching force f. The knot size $L_{knot}$ is primarily controlled by f. Two distinct regimes are identified. In one regime with $L_{knot}\ll L_{gap}$, the diffusion process is stepwise due to the discrete barriers induced by side chains. In the other regime with $L_{knot}\gg L_{gap}$, the diffusion is continuous and is slowed down due to the friction caused by side chains. The knot size in the small-gap regime changes non-monotonically with the length of the side chain. When the side chain length becomes more than a critical value, the knot shrinks to a small size and rearranged to have side chains outside the knot core to minimize excluded volume interactions. Overall, our results can guide the control of knots by side chains. Furthermore, knotting can be used to investigate molecular friction because knotting ensures significant contact between polymer segments in the knot core. [Preview Abstract] |
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M1.00149: Ferromagnetic rollers in a harmonic confinement Andreas Kaiser, Alexey Snezhko, Igor S. Aranson We present the emergence of flocking and global rotation in a system of rolling ferromagnetic microparticles energized by a vertical alternating magnetic field confined in a harmonic potential. By combing experiments and discrete particle simulations, we have identified primary physical mechanisms leading to the emergence of large-scale collective motion: spontaneous symmetry breaking of the clock / counterclockwise particle rotation, collisional alignment of particle velocities, and random particle re-orientations due to shape imperfections. We also emphasize a subtle role of rotational noise: While the low-frequency flocking appears to be noise-insensitive, the reentrant flocking happens to be noise-activated. Moreover, we uncover a new relation between collective motion and synchronisation. [Preview Abstract] |
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M1.00150: Jamming within Lattices Prairie Wentworth-Nice, Amy Graves Numerical methods are used in two dimensions to find the minimum energy configuration of soft bidisperse spheres, in the presence of lattices of fixed, pointlike particles. The lattice provides a supporting structure for the jammed configuration, resulting in changes in the jamming threshold. The excess coordination number and other properties of interest near jamming are calculated as a function of the lattice structure and number density. [Preview Abstract] |
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M1.00151: Silica Polypeptide Composite Particles as Responsive Materials for Jamming Transition Studies Alyssa Blake, Paul Russo Silica polypeptide composite particles consisting of an inorganic, colloidal silica core and an organic polypeptide shell can be used as model systems for studying biological and physical particle interactions. The polypeptide shell can undergo secondary conformational transitions between an alpha helix and random coil conformation, which results in a stimuli responsive material. Jamming of responsive materials has mainly used stimuli responsive polymers such as PNIPAM but these particles can undergo similar changes by switching the polypeptide conformation. Preliminary jamming studies of the polypeptide composite particles, using fluorescence photobleaching recovery, can be conducted to determine how responsive polymers effect the jamming phase transition of soft colloidal materials. [Preview Abstract] |
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M1.00152: Structured Liquids with pH-Triggered Reconfigurability Caili Huang, Brett Helms, Gregory Smith, Thomas Russell The ability to manipulate the shape of liquids in an external field and trapping these non-equilibrium shapes holds significant promise for the development of bicontinuous fluids, novel encapsulants for delivery systems, or all-liquid separations media. We find that the complementary electrostatic interactions of amine-terminated polydimethylsiloxane (PDMS-NH2) dissolved in a hydrophobic fluid (oil) and carboxlic acid functionalized nanoparticles (NPs) dispersed in water results in the formation of NP-surfactants (NPs with a well-defined number of ligands dynamically attached). The NP-surfactant assemblies are disordered yet dynamic, similar to those seen with NPs, and when the fluids are deformed, more NP-surfactants form at the interface such that, upon release of the deformation field, the NP-surfactants jam at the interface locking-in highly non-equilibrium shapes of the fluids. Such structured liquids can be reconfigured back into their equilibrium spherical shapes remotely using a water-soluble photoacid generator, which is triggered by light to disrupt the dynamic complementarity between the polymers and NPs in their jammed state. We present a detailed analysis of NP-surfactant dynamics as a function of pH. [Preview Abstract] |
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M1.00153: Kinetic growth of binary colloidal crystals in monolayer An Pham, Ryohei Seto, Eliot Fried, Benjamin B. Yellen A two-dimensional binary mixture of colloidal particles is a convenient experimental model for probing the dynamics of phase transitions in alloys. Here, we report a combined experimental and numerical study on the crystallization kinetics of binary colloidal particles suspended in a quasi-two-dimensional fluid film. To assess the size of the crystals, we use bond-order parameters and cluster aggregation algorithms to determine the mean domain sizes of crystals formed in different annealing conditions. Our study indicates that particle defects are the main source of frustration, limiting the growth of large crystals. We have grown crystals with almost 1500 particles in experiments; however simulations suggest that crystals having more than 10000 particles can be formed in a system free of particle defects. The average size and kinetic growth of domains are in agreement between experiments and simulations, when particle defects are included in simulation as the same concentration found in experiments. [Preview Abstract] |
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M1.00154: In Situ Visualization of the Growth and Fluctuations of Nanoparticle Superlattice in Liquids Zihao Ou, Bonan Shen, Qian Chen We use liquid phase transmission electron microscopy to image and understand the crystal growth front and interfacial fluctuation of a nanoparticle superlattice. With single particle resolution and hundreds of nanoscale building blocks in view, we are able to identify the interface between ordered lattice and disordered structure and visualize the kinetics of single building block attachment at the lattice growth front. The spatial interfacial fluctuation profiles support the capillary wave theory, from which we derive a surface stiffness value consistent with scaling analysis. Our experiments demonstrate the potential of extending model study on collective systems to nanoscale with single particle resolution and testing fundamental theories of condensed matter at a length scale linking atoms and micron-sized colloids. [Preview Abstract] |
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M1.00155: Modulating elastic band gap structure in layered soft composites using sacrificial interfaces Qianli Chen A wide range of engineered and natural composites exhibit a layered architecture whereby individual building blocks are assembled layer by layer using cohesive interfaces. The enhancement of toughness in those biological materials is partially attributed to wavy surfaces and cohesive interaction along the interfaces between bulk materials. In this study, we present a novel mechanism for evolving acoustic band gap structure in a model system of these composites through patterning the microstructure in a way that triggers non-planar interfacial deformations between the layers as they are stretched. Through the controlled deformation and growth of interlayer channels under macroscopic tension, we observe the emergence of multiple band gaps due to Bragg diffraction and local resonance. The variability of the band gap width develops due to the competition between stiffness changes as the hyperelastic material is changed and the evolving geometry due to the non-uniform deformation of the interfaces which lead to complex channel shapes and scattering response. We describe these phenomena in details for three example microstructures and discuss the implications of our approach for harnessing controlled deformation in modulating band gap properties of composite materials. [Preview Abstract] |
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M1.00156: How the Degree of Hydrophobicty Effects how Water Meets a Hydrophobic Surface Adele Poynor By definition hydrophobic substances hate water. Water placed on a hydrophobic surface will form a drop in order to minimize its contact area. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low-density depletion layer forms near the surface. We investigate the role of contact angle on depletion layer formation using the surface sensitive technique of Surface Plasmon Resonance [Preview Abstract] |
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M1.00157: Nematic phase in the CE-regime of colossal magnetoresistive manganites Emily Ochoa, Cengiz Sen, Elbio Dagotto We report nematic phase tendencies around the first order CE transition in the two-orbital double exchange model with Jahn-Teller phonons at electronic density $n=0.5$. Starting with a random state at high temperatures, we employ a careful cool-down method using a Monte Carlo algorithm. We then monitor the spin structure factor $S(q)$ of the CE phase as a function of temperature. Near the critical temperature, $S(q)$ grows with decreasing temperature for both right- and left-ordered CE ladders, followed by a spontaneous symmetry breaking into one or the other as the critical temperature is achieved. Below the critical temperature a pure CE state with a staggered charge order is obtained. Our results are similar to those observed in pnictides in earlier studies.[1]\\ \\ [1]Shuhua Liang, Adriana More, and Elbio Dagotto, Phys. Rev. Lett. {\bf 111}, 047004 (2013). [Preview Abstract] |
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M1.00158: Effective Binding Affinities of Mucin-like Polymers, A Computational Study Emiko Zumbro, Katharina Ribbeck, Alfredo Alexander-Katz Mucins are proteoglycan polymers found in mucus that play a key role in preventing infection, but their capabilities have yet to be mimicked by synthetic materials. Mucins have a dense bottlebrush structure that may display many low-affinity binding sites to interact with proteins such as lectins. Polyvalent binding site displays enhance the binding strength for low-affinity monovalent interactions but it is unknown how polyvalent system shape, size, and binding site density affect these interactions. Since the parameter space of polyvalent inhibitors is large and difficult to sample experimentally, we built a simulation to predict structural effects on binding affinities of polyvalent motifs. To evaluate the relative K$_{\mathrm{D}}$'s of polyvalent and monovalent inhibitors, we use a Brownian dynamics bead-spring model coupled with a reactive polymer-pathogen binding model. It bridges length and timescales and can sample large polymer systems that bind proteins at the sub-nanometer lengthscale. We are using competitive inhibition assays to validate the simulation and measure the enhanced inhibitory effect that polyvalency gives over free binding sites. This simulation gives design principles to optimize the structure and effectiveness of polyvalent inhibitors. [Preview Abstract] |
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M1.00159: DNA-linked NanoParticle Lattices with Diamond Symmetry: Stability, Shape and Optical Properties Hamed Emamy, Alexei Tkachenko, Oleg Gang, Francis Starr The linking of nanoparticles (NP) by DNA has been proven to be an effective means to create NP lattices with specific order. Lattices with diamond symmetry are predicted to offer novel photonic properties, but self-assembly of such lattices has proven to be challenging due to the low packing fraction, sensitivity to bond orientation, and local heterogeneity. Recently, we reported an approach to create diamond NP lattices based on the association between anisotropic particles with well-defined tetravalent DNA binding topology and isotropically functionalized NP. Here, we use molecular dynamics simulations to evaluate the Gibbs free energy of these lattices, and thereby determine the stability of these lattices as a function of NP size and DNA stiffness. We also predict the equilibrium shape for the cubic diamond crystallite using the Wulff construction method. Specifically, we predict the equilibrium shape using the surface energy for different crystallographic planes. We evaluate surface energy directly form molecular dynamics simulation, which we correlate with theoretical estimates from the expected number of broken DNA bonds along a facet. Furthermore we study the optical properties of this structure, e.g optical bandgap. [Preview Abstract] |
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M1.00160: Probing Thermal Properties of Hydrogels Laureen Meroueh, Shaoting LIn, Gang CHen, Xuanhe ZHao Hydrogels, with compositions ranging from 90-99\% water and the rest polymer and their liquid yet solid-like behavior promise various uses in the biomedical field, such as drug transport vehicles, cancer therapy, biosensors, medical electrodes, tissue engineering, etc. The structure of the polymer network that forms the hydrogel gives rise to different thermal transport properties of hydrogel. In this work, we utilize various methods to probe these thermal properties, such as time-domain thermoreflectance (TDTR) and transmission with embedded nanoparticles, laser flash analysis, and the classic hot-wire thermal conductivity measurement. These studies shed light on heat conduction mechanisms in hydrogels. [Preview Abstract] |
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M1.00161: Surface Tension of Alcohol-Water Mixtures Using Molecular Dynamics Simulations. Abdalla Obeidat, Hind Abu-Ghazleh Molecular dynamics is used to calculate the surface tension of alcohol-water mixtures. The gromos force fields of united atoms and all atoms of alcohols (methanol, ethanol, propanol, and acetone) has been used. The surface tension of alcohols has been calculated at different temperatures ranges from 200-300K, while for mixtures, the surface tension has been calculated at 298K with different concentrations. In all simulations, Gromacs is used with periodic boundary conditions in all dimensions. The simulated results are compared with the experimental values in literature, and with Monte-Carlo simulations as well. [Preview Abstract] |
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M1.00162: Retardation of Bulk Water Dynamics by Disaccharide Osmolytes Nimesh Shukla, Lee Chen, Enrico Pomarico, Majed Chergui, Christina Othon Bioprotective nature of disaccharides is hypothesized to derive from the modification of the hydrogen bonding network of water which protects biomolecules through lowered water activity at the protein interface. Using ultrafast fluorescence spectroscopy, we measured the relaxation of bulk water dynamics around the induced dipole moment of two fluorescent probes (Lucifer Yellow Ethylenediamine and Tryptophan). Our results indicate a reduction in bulk water reorganization rate of approximately 30{\%}. We observe this retardation in the low concentration regime measured at 0.1 and 0.25 M, far below the onset of glassy dynamics. This water structuring should be significant in crowded biological systems, contributing to a global change in protein energy landscape, resulting in a significant enhancement of protein stability under environmental stress. We observed similar dynamic reduction for two disaccharide osmolytes, sucrose and trehalose, with trehalose being the more effective in reducing solvation dynamics. [Preview Abstract] |
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M1.00163: Effect of a surface tension imbalance on a partly submerged cylinder Stoffel Janssens, Vikash Chaurasia, Eliot Fried We perform a force analysis of a circular cylinder which lays between a liquid--gas interface and acts as a barrier between a surfactant-free surface and a surfactant-loaded surface. The respective surfaces have uniform surface tensions $\gamma_a$ and $\gamma_b$ which generate a surface tension imbalance $\Delta \gamma=\gamma_a-\gamma_b$, also referred to as surface pressure. In addition to the general force analysis, we determine the effect of $\Delta\gamma$ on the load-bearing capacity of a floating cylinder upon sinking for a specific set of parameters. Moreover, we demonstrate that $\Delta \gamma$ induces a horizontal force component which in magnitude is equal to $\Delta \gamma$, when measured per unit length cylinder, and use an energetic argument to prove that this relation applies to prismatic bodies in general. [Preview Abstract] |
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M1.00164: Rheology of a nematic liquid crystal between two coaxial cylinders subjected to a pulsatile gradient pressure Daniel Martínez, Carlos Velázquez, Juan Adrián Reyes It is considered a nematic liquid crystal (NLC) filling the region between two coaxial cylinders. We study the rheological behavior of a NLC subjected to a pulsatile gradient pressure and an external radial electric field. For the 4’-n-pentyl-4-cyanobiphenyl (5CB) NLC, we consider soft anchoring and non-slip boundary conditions to numerically calculate the director’s alignment corresponding to the first and second frequency modes and the velocity profile induced by the flow. Finally, we calculate the apparent viscosity of the nematic. [Preview Abstract] |
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M1.00165: Bending, force recovery, and D-cones in origami inspired model geometries Theresa Eldar, damith rozairo, Andrew B. Croll The need for materials with advanced functionality has driven a considerable amount of modern materials science. One idea that has gained significant traction is combining of the ideas Origami and Kirigami with existing materials to build in advanced functionality. In most origami damage is induced in order to trap areas of high curvature in desirable locations in a material. However, the long term and dynamic consequences of local failure are largely unknown. In order to gauge the complex interplay of material properties, relaxation and failure in a set of model thin films, a series of bending and force recovery experiments were carried out. We focus on three materials; polydimethylsiloxane (PDMS), polycarbonate (PC), and polystyrene (PS) chosen for their varying responses to stress. We first measured the load bearing capacity of a single bend in each material, examining the force recovery of bends at various curvatures. Next we examined a ‘doubly’ folded system in which a single developable cone was created in a similar manner. While the D-cone clearly has massive local consequences for each system, it plays an insignificant role in the system’s overall behavior. Finally, we considered higher order combinations of d-cones, ridges and bends. [Preview Abstract] |
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M1.00166: Unusually large unit cell of lipid bicontinuous cubic phase: towards nature's length scales Hojun Kim, Cecilia Leal Lipid bicontinuous cubic phases are of great interest for drug delivery, protein crystallization, biosensing, and templates for directing hard material assembly. Structural modulations of lipid mesophases regarding phase identity and unit cell size are often necessary to augment loading and gain pore size control. One important example is the need for unit cells large enough to guide the crystallization of bigger proteins without distortion of the templating phase. In nature, bicontinuous cubic constructs achieve unit cell dimensions as high as 300 nm. However, the largest unit cell of lipid mesophases synthesized in the lab is an order of magnitude lower. In fact, it has been predicted theoretically that lipid bicontinuous cubic phases of unit cell dimensions exceeding 30 nm could not exist, as high membrane fluctuations would damp liquid crystalline order. Here we report non-equilibrium assembly methods of synthesizing metastable bicontinuous cubic phases with unit cell dimensions as high as 70 nm. The phases are stable for very long periods and become increasingly ordered as time goes by without changes to unit cell dimensions. [Preview Abstract] |
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M1.00167: A Computational Approach to Model Neutron Scattering Data from Lipid Bilayers Jan-Michael Carrillo, John Katsaras, Bobby Sumpter, Rana Ashkar The successful interpretation of multimodal characterization experiments of soft materials, such as lipid membranes in complex environments, requires the use of efficient computer simulation protocols, which are intended to supplant the spatially and temporally limited experimental measurements of membrane structures and dynamics. Here, we describe our coarse-grained MD simulation approach that can mimic neutron scattering data from unilamellar lipid vesicles over a range of bilayer rigidity. Specifically, we simulate vesicle form factors and membrane thickness fluctuations determined from small angle neutron scattering (SANS) and neutron spin echo (NSE) experiments, respectively. Our simulations accurately reproduce trends from experiments and lay the groundwork for investigations of more complex membrane systems. [Preview Abstract] |
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M1.00168: Structure and Stability of Colloid-Nanoparticle Mixtures Braden M. Weight, Alan R. Denton Colloidal particles can acquire charge through dissociation of counterions in a polar solvent. The resulting electrostatic interactions between particles stabilize the suspension against aggregation due to van der Waals forces and can affect physical properties. We explore the influence of added nanoparticles on structure and phase behavior of charge-stabilized colloidal suspensions. To reduce complexity, we model electrostatic interparticle interactions via effective Yukawa (screened-Coulomb) pair potentials, which implicitly include counterions and salt ions in the Debye screening constant. Within this coarse-grained model, we perform molecular dynamics simulations of mixtures of charged colloids and nanoparticles. Over ranges of parameters (charges, sizes, and concentrations of the two species), we analyze particle configurations to compute radial distribution functions and static structure factors. These structural properties reveal that nanoparticles tend to weaken correlations between colloids, thus destabilizing colloidal crystals. We further show that nanoparticles may be implicitly incorporated into an effective colloid-colloid pair potential to facilitate modeling of complex multicomponent systems and to guide experiments and applications to nanocomposite materials. [Preview Abstract] |
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M1.00169: Study of percolation behavior depending on molecular structure design Ji Woong Yu, Won Bo Lee Each differently designed anisotropic nano-crystals(ANCs) are studied using Langevin dynamic simulation and their percolation behaviors are presented. Popular molecular dynamics software LAMMPS was used to design the system and perform the simulation. We calculated the minimum number density at which percolation occurs(i.e. percolation threshold), radial distribution function, and the average number of ANCs for a cluster. Electrical conductivity is improved when the number of transfers of electrons between ANCs, so called "inter-hopping process", which has the considerable contribution to resistance decreases and the number of inter-hopping process is directly related with the concentration of ANCs. Therefore, with the investigation of relationship between molecular architecture and percolation behavior, optimal design of ANC can be achieved. [Preview Abstract] |
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M1.00170: Selective Plane Illumination Differential Dynamic Microscopy with Adaptive Optics Devynn Wulstein, Ryan McGorty We measure the dynamics of colloidal particles and DNA molecules using differential dynamic microscopy (DDM) on images captured through selective-plane illumination microscopy (SPIM). Combining DDM, a digital Fourier microscopy method, and SPIM, an optical sectioning microscopy technique, we can analyze the dynamics of concentrated suspensions of colloids and biopolymers. Further, selective-plane illumination differential dynamic microscopy (SPIDDM) exploits the spatial variations of the Gaussian light-sheet to obtain diffusion data over a wide range of spatial frequencies. Presented work focuses on in vitro measurements of colloids, DNA molecules and cytoskeleton networks. We have measured the collective dynamics of DNA in actin and microtubule networks spanning an order of magnitude in spatial frequencies. This work could easily extend to living samples given SPIDDM's sparing use of excitation light. We are currently adding adaptive optics into our light-sheet microscope with a deformable mirror. We discuss using adaptive optics for multiple purposes. The mirror corrects optical aberrations due to the sample holder and the sample. We are also using adaptive optics to optimize the three-dimensional point spread function for DDM measurements. Using the deformable mirror to purposefully introduce known aberrations could allow for a more precise measurement of colloidal or molecular dynamics in three-dimensions. [Preview Abstract] |
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M1.00171: The use of magnetic bottles to determine the susceptibility of paramagnetic nanoparticles Brandon Harris, H. Daniel Ou-Yang We present a new technique for determining the magnetic susceptibility of paramagnetic nanoparticles. Current methods of determining the magnetic properties of nanoparticles seem to be limited to ferromagnetic materials. Our magnetic bottles system uses microelectrodes to generate a highly localized magnetic field in a microfluidic environment. In our experiments, the fluorescently labeled paramagnetic nanoparticle concentration near the localized magnetic field can be measured using confocal fluorescence microscopy. The magnetic field distribution within the magnetic bottle, a region too small to be measured using conventional probes, can be calculated using COMSOL Multiphysics simulations. The magnetic field distribution can also be independently measured using paramagnetic nanoparticles of a known susceptibility. When a paramagnetic nanoparticle suspension is exposed to a magnetic field, the nanoparticle concentration will follow a Boltzmann distribution. The energy factor in the Boltzmann distribution is proportional to the product of the magnetic susceptibility and the square of the magnetic field. This method can be used to measure the susceptibility of any paramagnetic nanoparticle from its density distribution in a known magnetic field. [Preview Abstract] |
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M1.00172: Biomedical Applications of Nanoparticles Ashley Rice, Ana Oprisan, Sorinel Oprisan, Cèdric Giraudet, Fabrizio Croccolo Nanoparticles of iron oxide have a high surface area and can be controlled by an external magnetic field. Since they have a fast response to the applied magnetic field, these systems have been used for numerous in vivo applications, such as MRI contrast enhancement, hyperthermia, drug delivery, and cell separation. We performed a total of six imaging experiments using direct imaging and shadowgraphy methods in order to investigate the concentration-driven fluctuations using magnetic nanoparticles in the absence and in the presence of a magnetic field. The direct imaging and shadowgraphy experimental setups both involved a glass cell filled with magnetic nanocolloidal suspension and water with the concentration gradient oriented against the gravitational field and a superluminescent diode (SLD) as the light source. We recorded the diffusion with a CCD camera and used a dynamic structure factor algorithm for image processing in order to extract the thermophysical properties such as the structure factor and the correlation time. The difference between the direct imaging method and the shadowgraphy method is the presence of an object on the CCD camera during direct imaging. Using the correlation time, we were able to determine the diffusion coefficient. [Preview Abstract] |
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M1.00173: The Role of Interaction Heterogeneity in the Self-Assembly of DNA-Functionalized Colloids Talid Sinno, Ian Jenkins, John Crocker Heterogeneity is generally considered to be a detrimental factor for the self-assembly of colloidal particles into ordered structures. While this is well-established for certain types of heterogeneity such as size polydispersity, here we show, using a combination of equilibrium and non-equilibrium simulations, that heterogeneity in the pairwise interaction strength among a collection of particles may in fact be useful for nucleation of crystalline phases. In particular, we consider interaction heterogeneities that may arise from density variations of DNA oligomers grafted on the surface of sub-micron spherical particles to drive self-assembly. The beneficial impact of interaction heterogeneity is shown to arise from a synergistic combination of two effects. First, we employ umbrella sampling simulations to show that heterogeneity strongly lowers the free energy barrier associated with the nucleation of crystals by the formation of strongly-bound small clusters. Concurrently, non-equilibrium growth simulations show that variations in the interaction strength between particles inhibit gelation and polycrystallinity by keeping the number of such nuclei low, allowing individual nuclei to grow unhindered. [Preview Abstract] |
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M1.00174: 3D coherent X-ray diffractive imaging of an Individual colloidal crystal grain A. Shabalin, J.-M. Meijer, M. Sprung, A. V. Petukhov, I. A. Vartanyants Self-assembled colloidal crystals represent an important model system to study nucleation phenomena and solid-solid phase transitions. They are attractive for applications in photonics and sensorics. We present results of a coherent x-ray diffractive imaging experiment performed on a single colloidal crystal grain. The full three-dimensional (3D) reciprocal space map measured by an azimuthal rotational scan contained several orders of Bragg reflections together with the coherent interference signal between them. Applying the iterative phase retrieval approach, the 3D structure of the crystal grain was reconstructed and positions of individual colloidal particles were resolved. We identified an exact stacking sequence of hexagonal close-packed layers including planar and linear defects. Our results open up a breakthrough in applications of coherent x-ray diffraction for visualization of the inner 3D structure of different mesoscopic materials, such as photonic crystals. [Preview Abstract] |
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M1.00175: Contrasting Drainage and Stratification in Horizontal Vs Vertical Micellar Foam Films Ewelina Wojcik, Subinuer Yilixiati, Yiran Zhang, Vivek Sharma Understanding and controlling the drainage kinetics of thin films is an important problem that underlies the stability, lifetime and rheology of foams and emulsions. ~In foam films formed with micellar solutions, the surfactant is present as interfacially-adsorbed layer at both liquid-air interfaces, as well as in bulk as self-assembled supramolecular structures called micelles. Ultrathin micellar films exhibit stratification due to confinement-induced structuring and layering of micelles. Stratification in micellar foam films is manifested as stepwise thinning over time, and it leads to the coexistence of flat domains with discretely different thicknesses. In this contribution we use Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols to visualize and analyze thickness transitions and variations associated with stratification in micellar foam films made with sodium dodecyl sulfate (SDS). We contrast the drainage and stratification dynamics in horizontal and vertical foam films, and investigate the role played by gravitational, viscous, interfacial and surface forces. [Preview Abstract] |
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M1.00176: Visualizing Nanoscopic Topography and Patterns in Freely Standing Thin Films. Subinuer Yilixiati, Yiran Zhang, Collin Pearsall, Vivek Sharma Thin liquid films containing micelles, nanoparticles, polyelectrolyte-surfactant complexes and smectic liquid crystals undergo thinning in a discontinuous, step-wise fashion. The discontinuous jumps in thickness are often characterized by quantifying changes in the intensity of reflected monochromatic light, modulated by thin film interference from a region of interest. Stratifying thin films exhibit a mosaic pattern in reflected white light microscopy, attributed to the coexistence of domains with various thicknesses, separated by steps. Using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols developed in the course of this study, we spatially resolve for the first time, the landscape of stratifying freestanding thin films. In particular, for thin films containing micelles of sodium dodecyl sulfate (SDS), discontinuous, thickness transitions with concentration-dependent steps of 5-25 nm are visualized and analyzed using IDIOM~protocols. We distinguish~nanoscopic rims, mesas and craters and show that the~non-flat features are sculpted by oscillatory, periodic, supramolecular structural forces that arise in confined fluids [Preview Abstract] |
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M1.00177: Graphene-based liquid crystal cell Rajratan Basu The two dimensional graphene-honeycomb structure can interact with the liquid crystal's (LC) benzene rings through $\pi -\pi $ electron stacking. This LC-graphene interaction gives rise to a number of interesting physical and optical phenomena in the LC. We show that monolayer graphene films impose planar alignment on the LC. On the other hand, graphene acts as a transparent conductor. We show that a graphene-based LC cell can be fabricated without using any aligning layers and ITO electrodes. Graphene itself can be used as the electrodes as well as the aligning layers, obtaining an electro-optic effect of the LC inside the cell. [Preview Abstract] |
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M1.00178: Dielectric Anistropy and Elastic Constants Near the Nematic-Smectic A Transition Angelo Visco, Rizwan Mahmood, Donald Zapien The present work examines the behavior of dielectric anisotropy and the elastic constants associated with the deformation of liquid crystal molecules under the influence of an AC electric field and measured by an Automatic Liquid Crystal Tester (ALCT). The systems investigated are of various concentrations of 5CB (4-Cyano-4'-pentylbiphenyl) and 8CB (4-octyl-4'-cyanobiphenyl) liquid crystal as a function of temperature. These studies are important due to the complexity of the coupling between the orientational (nematic) and positional (smectic A) order parameters that can drive this transition to be either continuous or discontinuous. Theoretically, NA transition is weakly first order due to nematic director fluctuations in semctic A phase. This is similar to the transition from normal to superconductor. Thus, there exists a triple point similar to He3/He4 mixtures. Moreover, despite more than four decades of intense work, our understanding of this complex and interesting problem remains unclear. \newline [Preview Abstract] |
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M1.00179: Switching of liquid crystal devices between reflective and transmissive modes Hui-Chi Lin, Chih-Hung Wang Transflective liquid crystal displays (LCD) are commonly known that each pixel is divided into reflective (R) and transmissive (T) subpixels. The R mode uses ambient light, while the T mode utilizes a backlight to display images. However, the division of the pixel decreases the light efficiency and the resolution. This study demonstrates a gelator-doped liquid crystal (LC) devices, that is switchable between R and T modes, without sub-pixel division. The R and T modes are designed to have bend configurations with phase retardation of $\pi $/2 and $\pi $, respectively. The phase retardation of a LC device can be varied and fixed by the thermoreversible association and dissociation of the gelator molecules. It is believed that the proposed device is a potential candidate for portable information systems. [Preview Abstract] |
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M1.00180: Investigating Confinement Effects on Cholesteric Liquid Crystals Kyle Kabasares, Charles Melton, Linda Hirst Liquid crystal (LC) droplets provide the ability to study how confinement can affect macroscopic properties studied previously only in bulk material. Understanding properties such as elasticity and topological defects are important from both a scientific and practical standpoint. Advances in material applications, both biological and electronic, rely on characterizing the properties of LC and other soft matter based materials. In this project, we studied chiral nematic, also known as cholesteric liquid crystal (CLC) droplets in a mixture with water. We observed the material properties through polarized light microscopy, and we characterize properties such as defect textures and phase transitions on CLC samples of varying concentration. This study illustrates a versatile approach to studying confinement and self-assembly which can possibly be extended to other soft matter materials. [Preview Abstract] |
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M1.00181: A study on the twisted-escape radial configuration of lyotropic chromonic liquid crystals confined to cylinders Rui Chang, Karthik Nayani, Jinxin Fu, Nils Persson, Elsa Reichmanis, Jung Ok Park, Mohan Srinivasarao Nematic liquid crystals commonly exhibit escape radial configuration when confined to cylinders with normal surface anchoring. Lyotropic chromonic liquid crystals confined to cylinders exhibit a departure from the escape radial configuration by developing a twist distortion. This symmetry-breaking configuration is distinguished by its birefringence pattern with an increase of the transmitted intensity in the center of the cylinder. The length distribution and the average length of chromonic aggregates were estimated from a model for self-assembling systems. The contrasting scaling of splay and bend elastic modulus with aggregation length leads to the changes in the director field and the birefringence pattern. For high concentrations, we observed a co-existence of the twisted escape radial configuration with the doubly twisted configuration. The anchoring violation in doubly twisted domains is rationalized by the weak anchoring strength which is overcome by means of the saddle splay contribution to the free energy. Our experiments enable the estimation of the normal anchoring strength with the help of numerical calculations. [Preview Abstract] |
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M1.00182: Cherenkov radiation in cholesteric induced by slow charged particles. Juan Adrian Reyes, Jorge-V Fonseca, Carlos Alberto Velazquez We have elaborated a model for calculating the radiated energy spectrum of a charged traveling particle in a cholesteric liquid crystal at constant velocity. For this purpose we have evaluated the polarization of the cholesteric induced by traveling charged particle which can be expressed in terms of the electric field of the particle moving within the cholesteric. We have established Maxwell equations governing the mentioned field in the reciprocal space and solve them in the small birefringence approximation. We have shown that there exists radiation for any particle speed value and have calculated the radiated energy for hypoluminic particle velocities. We have calculated the spectrum for which radiation is emitted in terms of the speed particle and the traveling particle angle and obtain also the distribution of energy radiated versus frequency, emission angle, particle speed angle and particle traveling angle with respect to the cholesteric helix. [Preview Abstract] |
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M1.00183: Translational and Rotational Diffusion of Cholesterol in Lipid Membranes Younghoon Oh, Bong June Sung Cholesterol introduces structural order and dynamic fluidity to lipid membranes. The translational and rotational diffusion of cholesterol relates closely to the structural order and fluidity. However, its diffusional behavior, especially the dynamic heterogeneity of cholesterol, remains elusive at a molecular level. In this work, we investigate the peculiar rotational dynamics of cholesterols and its relation to heterogeneous dynamics of binary component lipid membranes. We perform coarse-grained molecular dynamics simulations using Martini force fields. A previous study revealed that lipids underwent translational and rotational hopping motions in single component gel phase lipid membranes [1]. In the binary component lipid membranes, however, we find no hopping motions for lipids in liquid ordered and disordered phases. Interesting is that cholesterol undergoes rotational hopping motions regardless. We also find that the rotational hopping angle of cholesterol is about 120 degrees, which may be due to the asymmetric cross sectional structure of the cholesterol. [1] Y. Oh, J. Kim and B. J. Sung, Phys. Rev. E. 93, 012409 (2016) [Preview Abstract] |
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M1.00184: Effects of Cationic Pendant Groups on Ionic Conductivity for Anion Exchange Membranes: Structure−Conductivity Relationships Sojeong Kim, Soo-Hyung Choi, won bo Lee Anion exchange membranes(AEMs) have been widely studied due to their various applications, especially for Fuel cells. Previous proton exchange membranes(PEMs), such as Nafions® have better conductivity than AEMs so far. However, technical limitations such as slow electrode kinetics, carbon monoxide (CO) poisoning of metal catalysts, high methanol crossover and high cost of Pt-based catalyst detered further usages. AEMs have advantages to supplement its drawbacks. AEMs are environmentally friendly and cost-efficient. Based on the well-defined block copolymer, self-assembled morphology is expected to have some relationship with its ionic conductivity. Recently AEMs based on various cations, including ammonium, phosphonium, guanidinium, imidazolium, metal cation, and benzimidazolium cations have been developed and extensively studied with the aim to prepare high- performance AEMs. But more fundamental approach, such as relationships between nanostructure and conductivity is needed. We use well-defined block copolymer Poly(styrene-block-isoprene) as a backbone which is synthesized by anionic polymerization. Then we graft various cationic functional groups and analysis the relation between morphology and conductivity. [Preview Abstract] |
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M1.00185: Lipid structure, lateral order and intermembrane forces Uri Raviv Using solution x-ray scattering and advanced analysis tools, developed in our lab (J. Chem. Info. Modeling 56, 1518, 2016), we are investigating the high-resolution structure of charged and/or dipolar lipids under various aqueous solution conditions (Soft Matter, 7, 1512, 2011; Langmuir, 27, 7419, 2011;J. Phys. Chem. B, 115, 14501, 2011;Langmuir, 27, 14767, 2011;Langmuir, 28, 2604, 2012.;J. Phys. Chem. B, 116, 3519 , 2012;Soft Matter. 9, 10640, 2013;Langmuir, 30, 14725, 2014.;J. Phys. Chem. A, 120, 3390, 2016.). These conditions include, different salt solutions containing monovalent, multivalent, or polyvalent ions, as well as ionic liquids. We determine the electron density profile along the normal to the membrane plane and the spacing between bilayers when lamellar phases form. Using the osmotic stress method, we are determining the forces between these bilayers under different conditions and compare with the predicted interactions based on thermal fluctuations and a modified Poisson Boltzmann theory. This comparison reveals the extent of ion dissociation, entropic effects, membrane elastic properties, and the non electrostatic interactions between the ions and the lipid membranes. We are also revealing the lateral order within the bilayers, using solution wide angle x-ray scattering experiments and our advanced analysis tools. [Preview Abstract] |
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M1.00186: Synthetic Molecular Evolution of Membrane-Active Peptides William Wimley The physical chemistry of membrane partitioning largely determines the function of membrane active peptides. Membrane-active peptides have potential utility in many areas, including in the cellular delivery of polar compounds, cancer therapy, biosensor design, and in antibacterial, antiviral and antifungal therapies. Yet, despite decades of research on thousands of known examples, useful sequence-structure-function relationships are essentially unknown. Because peptide-membrane interactions within the highly fluid bilayer are dynamic and heterogeneous, accounts of mechanism are necessarily vague and descriptive, and have little predictive power. This creates a significant roadblock to advances in the field. We are bypassing that roadblock with synthetic molecular evolution: iterative peptide library design and orthogonal high-throughput screening. We start with template sequences that have at least some useful activity, and create small, focused libraries using structural and biophysical principles to design the sequence space around the template. Orthogonal high-throughput screening is used to identify gain-of-function peptides by simultaneously selecting for several different properties (e.g. solubility, activity and toxicity). Multiple generations of iterative library design and screening have enabled the identification of membrane-active sequences with heretofore unknown properties, including clinically relevant, broad-spectrum activity against drug-resistant bacteria and enveloped viruses as well as pH-triggered macromolecular poration. [Preview Abstract] |
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M1.00187: Amphiphilic polypeptoids connect lipid bilayers to rearrange unilamellar liposomes to closely spaced multilayered structures. Vijay John, Yueheng Zhang, Sunting Xuan, Donghui Zhang, Marzhana Omarova Hydrophobically modified polypeptoids (HMPs) are amphiphilic pseudo-peptidic macromolecules with hydrophobic groups attached randomly along the polypeptoid backbone. We show that these biocompatible polymers connect across lipid bilayers and thus form layered structures on liposomes. The transition from single bilayer to multiple bilayer structures is characterized by small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). We propose a mechanism whereby the HMPs insert their hydrophobic tails into adjacent bilayers and thereby serve as the connective glue between bilayers. At higher HMP concentrations, the liposomes are entirely disrupted into much smaller micelle-like structures through extensive hydrophobe insertion. Interestingly, these small structures can reattach to fresh unilamellar liposomes and self-assemble to form new two-bilayered liposomes reminiscent of two-bilayered organelles such as the nucleus in eukaryotic cells. The observations have significance to designing new nanoscale drug delivery carriers. Replace this text with your abstract body. [Preview Abstract] |
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M1.00188: Examination of Various Mobility Intervals to Establish Multiple Dynamic Time Scales in Supercooled Liquids Dillon Sanders, Jacop Eapen Investigations of string-like cooperative motion in supercooled liquids have mostly considered the fastest-moving, or most “mobile”, particles in the system. Previous analysis has noted the close association of the time scales associated with strings formed by these highly-mobile particles to the peak time of the non-Gaussian parameter, and by extension the alpha-relaxation time that characterizes the “cage-breaking” regime that occurs before the onset of diffusive motion. More recent work has uncovered the existence of other dynamic time scales in glassy systems that are associated with the dynamics of particles with very low mobility. In this work we consider the cooperative motion of particles over a wide range of mobilities, from the fastest-moving particles to those that are relatively slow, and establish the existence of multiple dynamic time scales arising from particular mobility intervals. We discuss the relationship between these time scales and other characteristic times of the system, such as the structural relaxation time associated with viscosity. Our analysis intends to shed light on the idea that the dynamics of less-mobile particles is the driving force behind the structural relaxation of glass-forming systems. [Preview Abstract] |
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M1.00189: Avoided criticality and slow relaxation in frustrated two dimensional models Ilya Esterlis, Steven Kivelson, Srinivas Raghu, Gilles Tarsus Frustration, and the associated phenomenon of ``avoided criticality'' have been proposed as an explanation for the dramatic relaxation slowdown in glass-forming liquids. To test this, we have undertaken a Monte-Carlo study of possibly the simplest such problem, the 2-dimensional XY model with frustration corresponding a small flux, $f$, per plaquette. At $f=0$, there is a Berezinskii-Kosterlitz-Thouless transition at $T^*$, but at any small but non-zero $f$, this transition is avoided, and replaced (presumably) by a vortex-ordering transition at much lower temperatures. We thus have studied the evolution of the dynamics for small $f$ as the system is cooled from above $T^*$ to below. While we do find strongly temperature dependent slowing of the dynamics as $T$ crosses $T^*$, and that simultaneously the dynamics becomes more complex, neither effect is anywhere nearly as dramatic as the corresponding phenomena in glass-forming liquids. At the very least, this implies that the properties of supercooled liquids must depend on more than the mere existence of an avoided transition. [Preview Abstract] |
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M1.00190: Frank-Kasper and other superlattice formations in a series of \textit{AB}$_{n}$ type giant molecules precisely constructed by functionalized nanoparticles. Stephen Cheng, Xueyan Feng, Ruimeng Zhang, Chih-Hao Hsu, Gengxin Liu, Tao Li A novel set of precisely defined \textit{AB}$_{n}$ type giant molecules has been designed and synthesized. They are consisted of one functionalized hydrophilic polyhedral oligomeric silsesquioxane (DPOSS) ($A)$ connected with different numbers of hydrophobic BPOSS cages ($B$, $n=$1-7). With variation of the number of coordinated hydrophobic POSS $B$, different superlattice structures could be formed at a sub-20-nm scale. For example, the superlattice structure of DPOSS-BPOSS$_{\mathrm{1}}$ can form a normal lamellar structure while DPOSS-BPOSS$_{\mathrm{2\thinspace }}$changes to a double-dyroids phase. With increasing the number of BPOSS, hexagonal close packed cylinder phase can be formed by DPOSS-BPOSS$_{\mathrm{3}}$. For DPOSS-BPOSS$_{\mathrm{4,\thinspace }}$DPOSS-BPOSS$_{\mathrm{5\thinspace }}$and DPOSS-BPOSS$_{\mathrm{6}}$, all of these giant molecules show the Frank-Kasper A15 phase, while DPOSS-BPOSS$_{\mathrm{7\thinspace }}$can assembly into a sigma phase. With deep understanding of this set of model \textit{AB}$_{n}$ type giant molecules with functional ``nano-atoms'', it is promising to construct new generations of giant molecules for further development of functional materials with desired structures and macroscopic properties. [Preview Abstract] |
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M1.00191: Numerical approach on dynamic self-assembly of colloidal particles Muhamet Ibrahimi, Serim Ilday, Ghaith Makey, Ihor Pavlov, Özgün Yavuz, Oguz Gulseren, Fatih Omer Ilday Far from equilibrium systems of artificial ensembles are crucial for understanding many intelligent features in self-organized natural systems. However, the lack of established theory underlies a need for numerical implementations. Inspired by a novel work$^{\mathrm{1}}$, we simulate a solution-suspended colloidal system that dynamically self assembles due to convective forces generated in the solvent when heated by a laser. In order to incorporate with random fluctuations of particles and continuously changing flow, we exploit a random-walk based Brownian motion model and a fluid dynamics solver prepared for games, respectively. Simulation results manage to fit to experiments and show many quantitative features of a non equilibrium dynamic self assembly, including phase space compression and an ensemble-energy input feedback loop. \begin{enumerate} \item Ilday, Serim, et al. \textit{APS March Meeting Abstracts}. 2016. \end{enumerate} [Preview Abstract] |
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M1.00192: Phase Behavior of Patchy Spheroidal Fluids. Thienbao Carpency We employ Gibbs-ensemble Monte Carlo computer simulation to assess the impact of shape anisotropy and particle interaction anisotropy on the phase behavior of a colloidal (or, by extension, protein) fluid comprising patchy ellipsoidal particles, with an emphasis on critical behavior. More specifically, we obtain the fluid-fluid equilibrium phase diagram of hard prolate ellipsoids having Kern-Frenkel surface patches under a variety of conditions and study the critical behavior of these fluids as a function of particle shape parameters. It is found that the dependence of the critical temperature on aspect ratio for particles having the same volume can be described approximately in terms of patch solid angles. In addition, ordering in the fluid that is associated with particle elongation is also found to be an important factor in dictating phase behavior. [Preview Abstract] |
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M1.00193: Controlled steering and propulsion of nanohelices Tapio Ala-Nissil\"a, Maria Michiko Alcanzare, Vaibhav Thakore Fuel-free controlled propulsion and steering of in aqueous solutions have been experimentally demonstrated for microscale particles by taking advantage of the coupled rotational and translational motion. The grand challenge at the nanoscale is overcoming thermal effects which can alter the direction of motion and interfere with the propulsion. The hybrid lattice-Boltzmann Molecular Dynamics method with full hydrodynamic interactions and thermal fluctuations [1] is used to demonstrate that controlled propulsion and maneuverability is possible for helically shaped structures at a sufficiently high P\'eclet number. The magnetic helical structure interacts with a rotating magnetic field. The interaction induces a torque that propels the helix in the fluid through the coupled rotational and translational motion. The P\'eclet number and the propulsive velocity are quantified at various field frequencies. The propulsive velocities are observed to be linear with the field frequencies up to a certain step-out frequency which depends on the helical structure.\\ 1. S.T.T. Ollila {\it et al.}, J. Chem. Phys. {\bf 134}, 064902 (2011); Multiscale Model. Simul. {\bf 11}, 213 (2013). [Preview Abstract] |
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M1.00194: Analysis of Local Rheological Properties of Crystalline Polymer by Dynamic X-ray Diffraction Shuhei Nozaki, Ken Kojio, Atsushi Takahara, Kohki Aoyama, Hiroyasu Masunaga Polymer materials form the hierarchical structure from nanometer to micrometer scales. Since the mechanical properties are correlated with the hierarchical structure, the precise evaluation of mechanical properties considering the size of the hierarchical structure is important. Recently, the time-resolved measurement of molecular aggregation structure using microbeam have been carried out diffraction at synchrotron radiation facilities. Analyzing change of crystal structure using microbeam X-ray diffraction under cyclic dynamic strain will give rheological properties of local region of crystalline polymers. In this study, a time-resolved microbeam wide-angle X-ray diffraction was used to study local rheological properties for inside and outside of isotactic polypropylene (iPP) spherulite under cyclic dynamic strain. Local dynamic storage modulus (E’) and loss modulus (E”) were obtained from change of d-spacing in (110) planes of alpha form of iPP crystal for inside and outside of iPP spherulite at a condition with strain of 0.01 and 0.1 Hz. The local E’ values were larger than those obtained from dynamic viscoelastic property measurement. This might be due to lower modulus of amorphous phase of bulk iPP. [Preview Abstract] |
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M1.00195: Access resistance in ion transport through graphene nanopores Subin Sahu, Michael Zwolak The effect of the bulk electrolyte on the measured resistance of a nanopore has been a long-standing challenge. Typically, this effect is referred to as the access resistance and -- under certain strict assumptions regarding the potential and the geometry -- depends only on the pore radius. Simulations are often employed to compare the resistance of different ion types, protein configurations, or pore geometries. We demonstrate that there is a bulk contribution within the sizes accessible with simulations. We show how to make use of the standard series resistance formula to extract the pore resistance (that includes both the pore and the access resistance). These results shed light on common assumptions used in computing access resistance, as well as on the proper simulation of ion transport. [Preview Abstract] |
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M1.00196: STATISTICAL AND NONLINEAR PHYSICS |
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M1.00197: Microscopic Statistical Characterisation of the Congested Traffic Flow and Some Salient Empirical Features Bo Yang, Ji Wei Yoon, Christopher Monterola We present large scale, detailed analysis of the microscopic empirical data of the congested traffic flow, focusing on the non-linear interactions between the components of the many-body traffic system. By implementing a systematic procedure that averages over relatively unimportant factors, we extract the effective dependence of the acceleration on the gap between the vehicles, velocity and relative velocity. Such relationship is characterised not just by a few vehicles but the traffic system as a whole. Several interesting features of the detailed vehicle-to-vehicle interactions are revealed, including the stochastic distribution of the human responses, relative importance of the non-linear terms in different density regimes, symmetric response to the relative velocity, and the insensitivity of the acceleration to the velocity within a certain gap and velocity range. The latter leads to a multitude of steady-states without a fundamental diagram. The empirically constructed functional dependence of the acceleration on the important dynamical quantities not only gives the detailed collective driving behaviours of the traffic system, it also serves as the fundamental reference for the validations of the deterministic and stochastic microscopic traffic models in the literature. [Preview Abstract] |
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M1.00198: Low-temperature linear thermal rectifiers based on Coriolis forces Suwun Suwunnarat, Huanan Li, Ragnar Fleischmann, Tsampikos Kottos We investigate thermal rectification due to a Coriolis force in a setup of three-terminal symmetric harmonic junctions. By adjusting the angular velocity of the rotating platform, which induces a Coriolis force, we can control the preferred heat transport direction. The concept is demonstrated by using a simple three-terminal triangular lattice. [Preview Abstract] |
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M1.00199: Distortion of online reputation by excess reciprocity: quantification and estimation of unbiased reputation Tomaso Aste, Giacomo Livan, Fabio Caccioli The peer-to-peer (P2P) economy relies on establishing trust in distributed networked systems, where the reliability of a user is assessed through digital peer-review processes that aggregate ratings into reputation scores. Here we present evidence of a network effect which biases digital reputations, revealing that P2P networks display exceedingly high levels of reciprocity. In fact, these are so large that they are close to the highest levels structurally compatible with the networks’ reputation landscape. This indicates that the crowdsourcing process underpinning digital reputation is significantly distorted by the attempt of users to mutually boost reputation, or to retaliate, through the exchange of ratings. We uncover that the least active users are predominantly responsible for such reciprocity-induced bias, and that this fact can be exploited to obtain more reliable reputation estimates. Our findings are robust across different P2P platforms, including both cases where ratings are used to vote on the content produced by users and to vote on user profiles. [Preview Abstract] |
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M1.00200: Modeling antibody diversity during affinity maturation in the germinal center Luis Miguel De Jesús Astacio, Assaf Amitai, Mehran Kardar The adaptive immune system is responsible for the construction of new antibodies capable of targeting an almost limitless repertoire of pathogens. In response to an infection, naive B cells incorporate into germinal centers and their clones undergo affinity maturation. During this stage, antibodies with higher affinity survive while those with lower affinity undergo apoptosis. Furthermore, a recent study suggests that the affinity maturation process is stochastic and akin to a rapid form of evolution. Our project focused on understanding how antibody diversity changes with respect to time during affinity maturation. A series of computational models of ascending complexity were developed and implemented in Matlab and were used to extract descriptive statistical parameters of the simulated process. It was shown that a probabilistic description of the affinity maturation process is possible by means of computational simulations and that many important statistical values can be derived from such models, including the evolution of diversity with respect to time, coexistence probability of multiple types and mean time for fixation to one type. The project represents an opportunity to understand how the adaptive immune system efficiently produces new antigen-specific antibodies. [Preview Abstract] |
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M1.00201: Microbes under pressure Oskar Hallatschek In natural settings, microbes tend to grow in dense populations where they need to push against their surroundings to accommodate space for new cells. The associated contact forces play a critical role in a variety of population-level processes, including biofilm formation, the colonization of porous media, and the invasion of biological tissues.Here, we reveal a collective mechanism of confinement that promotes the build-up of large mechanical pressures in microbial populations. Microfluidic experiments on budding yeast populations in space-limited environments show that self-driven jamming arises from the gradual formation and sudden collapse of force chains driven by microbial proliferation, extending the framework of driven granular matter. The resulting contact pressures can become large enough to slow down cell growth, to delay the cell cycle in the G1 phase, and to strain or even destroy the microenvironment through crack propagation. Finally, we discuss how discuss how collective pushing dynamics can promote the emergence of mutational jackpot events. Our results suggest that self-driven jamming and build-up of large mechanical pressures is a natural tendency of microbes growing in confined spaces, contributing to microbial pathogenesis and biofouling. [Preview Abstract] |
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M1.00202: Defect interactions in anisotropic two-dimensional fluids Ralf Stannarius, Kirsten Harth Disclinations in liquid crystals bear striking analogies to defect structures in a wide variety of physical systems, they are excellent models to study fundamental properties of defect interactions. Freely suspended smectic C films behave like quasi 2D polar nematics. An experimental procedure is introduced to capture high-strength disclinations in localized spots. After they are released in a controlled way, the motion of the mutually repelling topological charges is studied. We demonstrate that the classical models, based on elastic one-constant approximation, fail to describe their dynamics correctly. In realistic liquid crystals, the models work only in ideal configurations. In general, additional director walls modify interactions substantially. [Preview Abstract] |
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M1.00203: Architected Squirt-flow Materials for Energy Dissipation Tal Cohen, Patrick Kurzeja, Katia Bertoldi Hetrogenieties at the pore level of fluid saturated materials have been shown to generate a dominant mode of dissipation by a local flow mechanism known as squirt-flow. In the present study we investigate the internal void architectures that lead to squirt-flow, in an attempt to maximally enhance the material dissipation. We consider materials that can elastically undergo large deformations and thus we account for both material and geometrical nonlinearities. We show, by combination of analytical and numerical investigation, that an intelligent design of the internal structure can dramatically increase the dissipation levels in comparison with equivalent homogeneous internal designs. Therefore we suggest squirt-flow as a promising mechanism to be incorporated in future architected materials that can effectively and reversibly dissipate energy. [Preview Abstract] |
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M1.00204: Low Reynolds Number Bacterial Robots Grant Giesbrecht, Katha Ni, Isaac Vock, Bruce Rodenborn The dynamics of prokaryotic motility in a fluid is important in a wide range of fields. Our experiment models the locomotion of bacteria with a robotic swimmer made using a computer controlled DC motor that drives a helical flagellum formed from welding wire. Because of its small size, a bacterium swimming in water is like our robot swimming in corn syrup. We compensate for the size difference by placing the robot in highly viscous silicone oil. Previous research measured helical propulsion of a swimmer far from a boundary (Rodenborn et al., PNAS 2013). However proximity to a boundary strongly affects bacterial swimming. We have designed a system to precisely control the distance from the flagellum to the tank wall, and have made some of the first macroscopic measurements of boundary effects on helical propulsion. [Preview Abstract] |
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M1.00205: Realization of an information ratchet under real time feedback control Govind Paneru, Dong Yun Lee, Hyuk Kyu Pak We have designed an information ratchet that is capable of transporting a Brownian particle in one direction and extracting work from a single heat bath by utilizing the information about the microscopic state of the system. The feedback control system is capable of performing an error-free measurements with a precision of 2 nm or less. By taking account of the unavailable information, we have demonstrated that the system achieves an upper bound of extractable work and thereby validates the generalized second law of thermodynamics. We have also confirmed the generalized Jarzyski equality for the case of error-free measurements. [Preview Abstract] |
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M1.00206: Feedback trap using optical force Yonggun Jun, Hyuk Kyu Pak Recently, the feedback trap using electrophoretic force (ABEL trap) has been used in the experimental study of non-equilibrium thermodynamics such as Landauer's erasure principle. This trap can trap and manipulate a small particle in solution by canceling the Brownian fluctuations. Here, we propose a simple way to control a bead using optical force with feedback and show the dynamics of a single particle in the virtual potential. [Preview Abstract] |
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M1.00207: Examining Correlation between Information Entropy and Thermodynamic Entropy in Liquid Crystal Jiajing Guan, John Cressman Here we report on experiments in electroconveciting liquid crystals where we acquired data that enabled the simultaneous calculation of the information and thermodynamic entropy. Although most theories are based in thermodynamic entropy, information entropy is often easier to ascertain. Therefore, we aimed to test whether information entropy could be used as a surrogate for thermodynamic entropy. Our initial investigations established that both entropy measures have related fluctuations during large transitions. We have further examined the dependence of information and thermodynamic entropy on driving voltages. Finally, we have studied the correlation between temporal fluctuations in information and thermodynamic entropy while the crystal is driven in a steady state. [Preview Abstract] |
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M1.00208: A model for Entropy Production, Entropy Decrease and Action Minimization in Self-Organization Georgi Georgiev, Atanu Chatterjee, Thanh Vu, Germano Iannacchione In self-organization energy gradients across complex systems lead to change in the structure of systems, decreasing their internal entropy to ensure the most efficient energy transport and therefore maximum entropy production in the surroundings. This approach stems from fundamental variational principles in physics, such as the principle of least action. It is coupled to the total energy flowing through a system, which leads to increase the action efficiency. We compare energy transport through a fluid cell which has random motion of its molecules, and a cell which can form convection cells. We examine the signs of change of entropy, and the action needed for the motion inside those systems. The system in which convective motion occurs, reduces the time for energy transmission, compared to random motion. For more complex systems, those convection cells form a network of transport channels, for the purpose of obeying the equations of motion in this geometry. Those transport networks are an essential feature of complex systems in biology, ecology, economy and society. [Preview Abstract] |
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M1.00209: Weak magnetic field effect on the growth of bacteria on plain glass and nano-ripple glass pattern. Iram Saleem, Samina Masood, Derek Smith, Wei-Kan Chu Bacterial growth on plain glass surface and glass nano-ripple structure fabricated by gas cluster ion beam irradiation shows more growth on the nanostructure. We compared the growth of two gram negative rod-shaped bacteria, E.coli and Pseudomonas aeruginosa. Bacteria gets trapped between the nano grooves and grows in size making larger colonies. We also studied the effect of weak magnetic field (uniform and non-uniform) on the growth of the two bacteria, E.coli and Pseudomonas aeruginosa, on the nano-ripple glass surface. Different behavior in the bacterial growth~was observed~on the glass nano-ripple surface inside and outside the magnetic field. Bacteria seems to grow more in the absence of the magnetic field. Bacteria growing on a nano ripple pattern inside the magnetic field tends to make smaller colonies. Uniform magnetic field shows uniform growth on the substrate and much smaller colonies. Magnetic field effects the growth of bacteria on the nano ripple substrate by decreasing the size of the colonies [Preview Abstract] |
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M1.00210: A Computational Study of Phenotype Switching in Bacillus Subtilis Biofilm Howard Smith, xiaoling Wang, Yi Jiang Bacillus Subtilis (B. Subtilis), is known to differentiate into three main phenotypes during biofilm growth. Novel techniques to track the spatial and temporal evolution of the three main phenotypes exhibited by B. Subtilis have been developed. However, the techniques do not explain the environmental causes of the phenotype switching and how this leads to the spatiotemporal organization of the biofilm. We hypothesize that cells switch their phenotype according to nutrients and autoinducer levels. We test the hypothesis using a hybrid agent-based and continuous model. The bacteria in our model are individual cells that can (i) grow and divide by the intake of nutrients, (ii) produce and secrete EPS, (iii) form spores and (iv) produce an auto inducer. Using a threshold for nutrient and thresholds for autoinducers, we were able to reproduce the experimental spatiotemporal dynamics. From our simulations we observed that in order to reproduce experimental results, two different autoinducers were necessary. The results also suggest that low-EPS producing biofilms generally obtained higher cell populations. Furthermore, most of the cells that become spore forming cells arise from matrix producing cells. [Preview Abstract] |
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M1.00211: GPU-Accelerated Hybrid Algorithm for 3D Localization of Fluorescent Emitters in Dense Clusters Yoon Jung, Anthony Barsic, Rafael Piestun, Nikta Fakhri In stochastic switching-based super-resolution imaging, a random subset of fluorescent emitters are imaged and localized for each frame to construct a single high resolution image. However, the condition of non-overlapping point spread functions (PSFs) imposes constraints on experimental parameters. Recent development in post processing methods such as dictionary-based sparse support recovery using compressive sensing has shown up to an order of magnitude higher recall rate than single emitter fitting methods. However, the computational complexity of this approach scales poorly with the grid size and requires long runtime. Here, we introduce a fast and accurate compressive sensing algorithm for localizing fluorescent emitters in high density in 3D, namely sparse support recovery using Orthogonal Matching Pursuit (OMP) and L1-Homotopy algorithm for reconstructing STORM images (SOLAR STORM). SOLAR STORM combines OMP with L1-Homotopy to reduce computational complexity, which is further accelerated by parallel implementation using GPUs. This method can be used in a variety of experimental conditions for both in vitro and live cell fluorescence imaging. [Preview Abstract] |
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M1.00212: Glass-like dynamics in the folded state of human interphase chromosome Guang Shi, Changbang Hyeon, Devarajan Thirumalai Genomic DNA in eukaryotes cell is wrapped around nucleosomes and packaged in cell nucleus. Advances in Hi-C and super resolution microscopy have given quantitative information on the folded state of chromosome as well as its dynamics on length scale from several kilo base pairs to hundreds of millions of base pairs. We created a copolymer model to study organization and dynamics of human interphase chromosome. We show that compartments seen in Hi-C experiment is a manifestation of micro-phase separation between active and repressive loci. The dynamics in the package state has all the characteristics of glasses. An indication of glassiness is the crossover from confined diffusion to the subdiffusion in the motion of the chromatin loci. The glassiness of chromosome dynamics provides a balance between stability and mobility on biologically relevant time scale. [Preview Abstract] |
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M1.00213: Mobility and Conformational Dynamics of large DNA diffusing through Cytoskeletal Networks Kathryn Regan, Shea Ricketts, Devynn Wulstein, Ryan McGorty, Rae M. Robertson-Anderson The high concentrations of proteins crowding cells greatly influence intracellular DNA dynamics. These crowders, ranging from small mobile proteins to large cytoskeletal filaments such as semiflexible actin and rigid microtubules, can hinder diffusion and induce conformational changes in DNA. The rigidity, mobility, and concentration of crowders all play a role in DNA transport, yet previous studies have mainly focused on the effect of small mobile crowders on transport. At the same time the rigid cytoskeleton has been identified as a key factor suppressing viral transfection and gene delivery. Here, we use fluorescence microscopy and custom single-molecule conformational tracking algorithms to measure center-of-mass transport and time-varying conformational sizes and shapes of single 115 kbp DNA molecules diffusing in networks of actin filaments and microtubules. We determine the dependence of protein concentration (6 -- 23 $\mu $M) and rigidity (actin vs microtubules) on DNA dynamics. Corresponding measurements with monomeric actin and tubulin identify the roles that network rigidity versus excluded volume play in transport. Initial results show that crowding by microtubules induces anomalous transport and larger, slower conformational fluctuations of DNA. [Preview Abstract] |
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M1.00214: Changes in the Coherent Dynamics of Nanoconfined Room Temperature Ionic Liquids Kevin Vallejo, Melissa Cano, Song Li, Gernot Rotner, Antonio Faraone, Jose Banuelos Confinement and temperature effects on the coherent dynamics of the room temperature ionic liquid (RTIL) [C$_{10}$MPy$^{+}$] [Tf$_{2}$N$^{-}$] were investigated using neutron spin-echo (NSE) in two silica matrices with different pore size. Several intermolecular forces give rise to the bulk molecular structure between anions and cations. NSE provided dynamics (via the coherent intermediate scattering function) in the time range of 0.004 to 10 ns, and at Q-values corresponding to intermediate range ordering and inter- and intra-molecular length scales of the RTIL. Pore wall effects were delineated by comparing bulk RTIL dynamics with those of the confined fluid in 2.8 nm and 8 nm pores. Analytical models were applied to the experimental data to extract decay times and amplitudes of each component. We find a fast relaxation outside the experiment time window, a primary relaxation, and slow, surface-induced dynamics, which all speed up with increased temperature, however, the temperature dependence differs between bulk and confinement. This study sheds light on the structure and dynamics of RTILs and is relevant to the optimization of RTILs for green technologies and applications. [Preview Abstract] |
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M1.00215: Dynamical Properties of Magnetized 2-Dimensional one component Plasma Girija Dubey, Godfrey Gumbs, Vassilios Fessatidis Molecular dynamics simulation are used to examine the effect of a uniform perpendicular magnetic field on a two-dimensional interacting electron system. In this simulation we include the effect of the magnetic field claasically through the Lorentz force. Both the Coulomb and the magnetic are included dirctly in the electron dynamics to study their combined effect on the dynamical and static properties of the 2D system.Results are presented for the velocity auto correlation function, the root mean square displacement, self correlation function and pair correlation function in the presence and absence of an external magnetic field. Our simulation results, clearly show that the external magnetic field has no effect on the static properties, but it affects the dynamics. [Preview Abstract] |
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M1.00216: Crystalline-gel-molten phase transitions of water in calcium dipicolinate (Ca-DPA) Subodh Tiwari, Ankit Mishra, Chunyang Sheng, Pankaj Rajak, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta The heat resistance of bacterial spores directly correlates to the protoplast dehydration and presence of dipicolinic acid (DPA) and its associated metal salts at the core. Bacteria's structural integrity in moist heat conferred by high concentration of DPA and calcium DPA salts depends on the properties are additional water molecules and temperature. In our reactive MD simulations, we characterize different possible phases and the transport properties of water molecules. We observed solid-gel and gel-liquid phase transitions of the hydrated Ca-DPA system. These simulations reveal monotonically decreasing solid-gel-liquid transition temperatures with increasing cell hydration, reflecting the experimental trend of moist-heat resistance of bacterial spores. We also observed that the calcification of bacterial spores further increases the transition temperatures. [Preview Abstract] |
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M1.00217: Boundary mediated position control of traveling waves Steffen Martens, Alexander Ziepke, Harald Engel Reaction control is an essential task in biological systems and chemical process industry. Often, the excitable medium supporting wave propagation exhibits an irregular shape and/or is limited in size. In particular, the analytic treatment of wave phenomena is notoriously difficult due to the spatial modulation of the domain's. Recently [S. Martens et al., PRE \textbf{91}, 022902; JCP \textbf{145}, 094108], we have provided a first systematic treatment by applying asymptotic perturbation analysis leading to an approximate description that involves a reduction of dimensionality; the $3$D RD equation with spatially dependent NFBCs on the reactants reduces to a $1$D reaction-diffusion-advection equation. Here, we present a novel method to control the position $\phi(t)$ of traveling waves in modulated domains according to a prespecified protocol of motion. Given this protocol, the ``optimal'' geometry of reactive domains $Q(x)$ is found as the solution of the perturbatively derived equation of motion. Noteworthy, such a boundary control can be expressed in terms of the uncontrolled wave profile and its propagation velocity, rendering detailed knowledge of the reaction kinetics unnecessary. [Preview Abstract] |
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M1.00218: The Ring of Fire: The Effects of Slope upon Pattern Formation in Simulated Forest Fire Systems Robin Morillo, Niklas Manz We report about spreading fire fronts under sloped conditions using the general cellular automaton model and data from physical scaled-down experiments. Punckt \textit{et al.} published experimental and computational results for planar systems [\textit{Wildfires in the Lab: Simple Experiment and Models for the Exploration of Excitable Dynamics}, J.\ Chem.\ Educ.\ \textbf{92}(8), 1330-1337, 2015] and our preliminary results confirmed the expected speed-slope dependence of fire fronts propagating up or down the hill with a cut-off slope value above which no fire front can exist. Here we focus on two fascinating structures in reaction-diffusion systems: circular expanding target pattern and rotating spirals. We investigated the behaviors of both structures with varied values for the slope of the forest and the homogeneity of the trees. For both variables, a range of values was found for which target pattern or spiral formation was possible. [Preview Abstract] |
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M1.00219: Flagellar dynamics reveal the distribution of chemotactic signaling molecule CheY-P in \textit{E. coli } Roshni Bano, Patrick Mears, Yann Chemla, Ido Golding \textit{E. coli }cells swim in a random walk consisting of "runs" --- during which the flagella that propel the cell rotate counter-clockwise (CCW) --- and "tumbles"--- during which one or more flagella rotate clockwise (CW). The tumbling frequency is modulated by the phosphorylation state of the signaling molecule CheY, which depends on the cell's environment. Phosphorylated CheY (CheY-P) binds to a flagellar motor and engenders a change in rotation state from CCW to CW. Despite advances in methods used to observe chemotactic signaling, it remains a challenge to measure the CheY-P level in cells directly. Here, we used an optical trap assay coupled with fluorescence microscopy to observe the dynamics of fluorescently labelled flagella in individual cells. By measuring the distribution of flagellar states in multi-flagellated cells and using our recent finding that each flagellar motor independently measures the cellular CheY-P concentration, we are able to extract the probability distribution of the CheY-P level in the cell. This analysis reveals the magnitude of fluctuations in chemotactic signaling in the live cell. We further investigate how this CheY-P distribution changes when cells encounter chemical gradients and perform chemotaxis. [Preview Abstract] |
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M1.00220: Tracking particles during avalanches on a conical bead pile Haidar Esseili, Avi Vajpeyi, Susan Lehman A conical bead pile subject to slow driving and an external magnetic field is used as a simple system to investigate the effect of cohesion on avalanche dynamics, including event size and time between events. Steel beads are dropped onto the pile from different heights, and avalanches are recorded by the change in mass as beads fall off the pile. Our experimental results for the probability distribution function compare well to the results of an analytic theory from a mean-field model of slip avalanches [Dahmen, Nat Phys 7, 554 (2011)]. The model also makes predictions about behaviors, such as event duration, which we previously could not measure experimentally. To more fully characterize the avalanching behavior of the pile over time, a high-speed camera is now in use to record the largest avalanches. To capture the full conical pile using a single camera, the camera with a wide-angle lens was placed nearly directly above the pile apex. We have modified particle tracking algorithms shared by N.T. Ouellette for our system and are tracking 5000 surface beads during each avalanche. Results from these new measurements allow a more complete characterization of avalanche behavior, including avalanche duration and the extent of the avalanche over the pile. [Preview Abstract] |
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M1.00221: Optimization of a Universal Granular Gripper Using Geometrical Inserts Edward Davis, Brian Utter, Kaixiang Shi, Ryder Winans, Charles Kim Universal robotic grippers utilize granular jamming in order to pick up objects of various sizes and fragility. Grains within an elastic membrane easily mold to an object's shape, and when evacuated, the granular material undergoes a jamming transition such that the gripper becomes rigid and grasps the object. We optimize the maneuverability and holding force of the device for the application of positioning retractors during thyroidectomies. We aim to improve on prior universal grippers by attaching retractors directly to an insert within the membrane to increase coupling with the granular medium. We present data for a range of insert geometries with the goal of achieving maximum holding force under vacuum and with maximal maneuverability without vacuum. [Preview Abstract] |
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M1.00222: Hannay's hoop revisited beyond asymptotics Hwan Bae, John F. Lindner A frictionless bead sliding on a rotating hoop is a classic example of an anholonomic system. Hannay's hoop has been studied in the asymptotic limit of very slow rotations. We study this system for \textit{arbitrary} rotations and elucidate the Hannay angle by computing the forces on the bead in both inertial and rotating frames. We consider ellipses, stadia and generalize to higher dimensions. We describe experimental realizations of the hoop anholonomy. [Preview Abstract] |
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M1.00223: Soliton creation, propagation, and annihilation in aeromechanical arrays of one-way coupled bistable elements Tessa Rosenberger, John F. Lindner We study the dynamics of mechanical arrays of bistable elements coupled one-way by wind. Unlike earlier hydromechanical unidirectional arrays, our aeromechanical one-way arrays are simpler, easier to study, and exhibit a broader range of phenomena. Soliton-like waves propagate in one direction at speeds proportional to wind speeds. Periodic boundaries enable solitons to annihilate in pairs in even arrays where adjacent elements are attracted to opposite stable states. Solitons propagate indefinitely in odd arrays where pairing is frustrated. Large noise spontaneously creates soliton- antisoliton pairs, as predicted by prior computer simulations. Soliton annihilation times increase quadratically with initial separations, as expected for random walk models of soliton collisions. [Preview Abstract] |
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M1.00224: Sliding on a spinning asteroid (geodesics on a rotating ellipsoid) Nathaniel Moore, John F. Lindner We computationally study the motion of a mass sliding on the surface of a rotating asteroid, with or without gravity, idealized as geodesics on a rotating ellipsoid. We identify qualitatively different families of motion, including chaotic and periodic motions, which generate visually striking patterns. We summarize the effects of gravity and spin on the dynamics. [Preview Abstract] |
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M1.00225: Period Doubling in Bubbling from a Submerged Nozzle Jordan Dennis, Laura Grace, Susan Lehman The timing of bubbles rising from a nozzle submerged in a viscous solution was measured to examine the period-doubling route to chaos in this system. A narrow nozzle was submerged in a mixture of water and glycerin, and nitrogen was supplied to the nozzle at a varying flow rate. The bubbles were detected using a laser and photodiode system; when the bubbles rise through the laser beam, they scatter the light so that the signal at the photodiode decreases. The period between bubbles as well as the duration of each bubble (a function of bubble size and bubble velocity) was determined, and examined as the nitrogen flow rate increased, for solutions with five different concentrations of glycerin. Bubbles were also recorded visually using a high-speed camera. Within the flow rates tested, we observed a bifurcation of the period to period-2 behavior for all solutions tested, and a further bifurcation to period-4 for all solutions except pure glycerin. The solution viscosity affected both the onset of the bifurcation and the precise bubble behavior during the bifurcation. Unusually, a short period/long period pair of bubbles recurring at a regular interval was sometimes observed in the low flow regime which is typically period-1, an observation which requires further investigation. [Preview Abstract] |
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M1.00226: Chaotic electrodes in photoconductive antenna for the enhancement of coherent terahertz beam Dong Ho Wu, Benjamin Graber, Louis Pecora, Christopher Kim In a curved waveguide trajectories of a particle (or eigenmodes of a wavefunction) diverge or converge exponentially with time so that the Lyapunov coefficient becomes larger or smaller than zero. Hence particles (or wave functions) tend to spread out with a convex waveguide or to concentrate with a convex shape waveguide. With a rippled waveguide containing both convex and concave shapes, one can control such divergent and convergent dynamic behavior of particles to modulate and concentrate them in particular locations. For the development of a new terahertz photoconductive antenna, we exploited such chaotic dynamics. A pair of chaotic electrodes in the photoconductive antenna drives thermal electrons away from the surface plasma producing a primary terahertz beam and makes the electrons to concentrate in locations slightly away from the plasma. While it minimizes the thermal electrons disrupting the plasma, the localized and concentrated electrons can be stimulated by the primary terahertz beam, and generate additional, spontaneous, coherent terahertz radiations through the process known as the Dicke superradiance. Hence our new photoconductive antenna with a pair of chaotic electrodes generates a noticeably enhanced coherent terahertz beam. [Preview Abstract] |
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M1.00227: Non-Perturbative approach to the distribution of zeros of the S-matrix of lossy chaotic cavities and its applications to coherent perfect absorption Yan Fyodorov, Suwun Suwunnarat, Tsampikos Kottos We employ the Random Matrix Theory framework to calculate the scattering matrix zeros of a chaotic cavity with a localized absorber embedded in it. Our approach extends beyond the perturbative weak-coupling limit of the cavity with the continuum via a finite number M of open channels and provides an insight for the optimal amount of loss needed to realize a chaotic coherent perfect absorbing trap. Our theoretical results are tested against and found to be in excellent agreement with simulations for two types of chaotic systems: a complex network of coupled resonators and quantum graphs with one absorption center. [Preview Abstract] |
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M1.00228: Abstract Withdrawn
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M1.00229: Time delayed Ensemble Nudging Method Zhe An, Henry Abarbanel Optimal nudging method based on time delayed embedding theory has shows potentials on analyzing and data assimilation in previous literatures. To extend the application and promote the practical implementation, new nudging assimilation method based on the time delayed embedding space is presented and the connection with other standard assimilation methods are studied. Results shows the incorporating information from the time series of data can reduce the sufficient observation needed to preserve the quality of numerical prediction, making it a potential alternative in the field of data assimilation of large geophysical models. [Preview Abstract] |
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M1.00230: Bridges in Random Graphs and Real Networks Angkun Wu, Liang Tian, Yang-Yu Liu A \emph{bridge} in a graph is an edge whose removal will disconnect the graph, i.e, increase the number of connected components. We analytically calculate the expected number of bridges for random graphs with arbitrary degree distributions. We also calculate the number of bridges for a wide range of real-world networks, finding that they typically have more bridges than their completely randomized counterparts. Finally, we define a new network metric, called \emph{bridgeness}, to quantify the network vulnerability from the edge attack perspective. We find that infrastructural networks (especially road networks and power grid networks) hold much larger maximum \emph{bridgeness} than other networks and their randomized counterpart. [Preview Abstract] |
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M1.00231: Open Markov processes: A compositional framework for non-equilibrium steady states. Blake Pollard Open Markov processes are generalizations of Markov processes in which probability can flow in and out of the system through some set of boundary states. We present a framework in which open Markov processes are morphisms in a category. Composition in this category provides a systematic way of constructing larger systems by composing smaller open systems. We describe a `black-box functor' which characterizes non-equilibrium steady states of open Markov processes in terms of the steady state flows of probability through the system. [Preview Abstract] |
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M1.00232: Resilience of Complex Networks Jianxi Gao, Baruch Barzel, Albert-Laszlo Barabasi Resilience, a system’s ability to adjust its activity to retain its basic functionality when errors, failures and environmental changes occur, is a defining property of many complex systems. Despite widespread consequences for human health, the economy and the environment, events leading to loss of resilience—from cascading failures in technological systems to mass extinctions in ecological networks—are rarely predictable and are often irreversible. These limitations are rooted in a theoretical gap: the current analytical framework of resilience is designed to treat low-dimensional models of a few interacting components, and is unsuitable for multi-dimensional systems consisting of a large number of components that interact through a complex network. Here we bridge this theoretical gap by developing a set of analytical tools with which to identify the natural control and state parameters of a multi-dimensional complex system, helping us derive an effective one-dimensional dynamics that accurately predicts the system’s resilience. The proposed analytical framework allows us systematically to separate the roles of the system’s dynamics and topology, collapsing the behavior of different networks onto a single universal resilience function. [Preview Abstract] |
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M1.00233: Frustration in Condensed Matter and Protein Folding S Lorelli, A Cabot, N Sundarprasad, C Boekema Using computer modeling [1-3] we study frustration in condensed matter and protein folding. Frustration is due to random and/or competing interactions. One definition of frustration is the sum of squares of the differences between actual and expected distances between characters. [3] If this sum is non-zero, then the system is said to have frustration. A simulation tracks the movement of characters to lower their frustration. Our research is conducted on frustration as a function of temperature using a logarithmic scale. At absolute zero, the relaxation for frustration is a power function for randomly assigned patterns or an exponential function for regular patterns like Thomson figures. These findings have implications for protein folding; we attempt to apply our frustration modeling to protein folding and dynamics. [4,5] We use coding in Python to simulate different ways a protein can fold. An algorithm is being developed to find the lowest frustration (and thus energy) states possible. [6,7] Research supported by SJSU {\&} AFC. [1] AK Dewdney, \textit{Scientific American } (1987) 112. [2] C Boekema \textit{et al,} \textit{Hpf Interact 26 }(1990) 345. [3] I M Suarez \textit{et al,} Conf Proc 2nd Woodward Conference, Springer Verlag NY 1990; Am Phys Soc Bull 35 (1990) 548. [4] J Claycomb {\&} JQP Tran, \textit{Introductory Biophysics }(2010). [5] LN Mazzoni {\&} L Casetti, \textit{Phys Rev Lett} (2006) [6] JL Van Hemmen, \textit{Phys Rev Lett }49 (1982) 4109. [7] M Mezard \textit{et al}, Spin Glass Theory and Beyond\textit{. World Scientific }(1987). [Preview Abstract] |
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M1.00234: An Laudau-Lifschitz theory based algorithm on calculating post-buckling configuration of a rod buckling in elastic media Shicheng Huang, Likun Tan, Nan Hu, Hannah Grover, Kevin Chu, Zi Chen This reserach introduces a new numerical approach of calculating the post-buckling configuration of a thin rod embedded in elastic media. The theoretical base is the governing ODEs describing the balance of forces and moments, the length conservation, and the physics of bending and twisting by Laudau and Lifschitz. The numerical methods applied in the calculation are continuation method and Newton's method of iteration in combination with spectrum method. To the authors' knowledge, it is the first trial of directly applying the L-L theory to numerically studying the phenomenon of rod buckling in elastic medium. This method accounts for nonlinearity of geometry, thus is capable of calculating large deformation. The stability of this method is another advantage achieved by expressing the governing equations in a set of first-order derivative form. The wave length, amplitude, and decay effect all agree with the experiment without any further assumptions. This program can be applied to different occasions with varying stiffness of the elastic medai and rigidity of the rod. [Preview Abstract] |
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M1.00235: Nonequilibrium phase transitions in a model of ecological and evolutionary dynamics Skye Tackkett, Hatem Barghathi, Thomas Vojta We employ large-scale Monte-Carlo simulations to study the extinction transition in a model describing the ecological and evolutionary dynamics of biopopulations. In the case of a neutral, time-independent fitness landscape, the extinction transition falls into the well-known directed percolation universality class. Temporal disorder (representing, for example, climate fluctuations) drastically changes the transition and leads to an exotic infinite-noise critical point. It is characterized by anomalously large fluctuations of the population size and logarithmically slow dynamics. [Preview Abstract] |
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M1.00236: Experimentally Modeling Black and White Hole Event Horizons via Fluid Flow Marc E. Manheim, John F. Lindner, Niklas Manz We will present a scaled down experiment that hydrodynamically models the interaction between electromagnetic waves and black/white holes. It has been mathematically proven that gravity waves in water can behave analogously to electromagnetic waves traveling through spacetime. In this experiment, gravity waves will be generated in a water tank and propagate in a direction opposed to a flow of varying rate. We observe a noticeable change in the wave’s spreading behavior as it travels through the simulated horizon with decreased wave speeds up to standing waves, depending on the opposite flow rate. Such an experiment has already been performed in a 97.2 cubic meter tank [Rousseaux et al., Observation of Negative-frequency Waves in a Water Tank: A Classical Analogue to the Hawking Effect?, New J. Phys. 10(5), 053015 (2008)]. We reduced the size significantly to be able to perform the experiment under normal lab conditions. [Preview Abstract] |
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M1.00237: Percolation Modeling of Self-Damaging of Composite Materials. Sergii Domanskyi, Vladimir Privman We propose the concept of autonomous self-damaging in ``smart'' composite materials, controlled by activation of added nanosize ``damaging'' capsules. Percolation-type modeling approach earlier applied to the related concept of self-healing materials, is used to investigate the behavior of the initial material's fatigue. We aim at achieving a relatively sharp drop in the material's integrity after some initial limited fatigue develops in the course of the sample's usage. Our theoretical study considers a two-dimensional lattice model and involves Monte Carlo simulations of the connectivity and conductance in the high-connectivity regime of percolation. We give several examples of local capsule--lattice and capsule--capsule activation rules and show that the desired self-damaging property can only be obtained with rather sophisticated ``smart'' material's response involving not just damaging but also healing capsules. [Preview Abstract] |
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M1.00238: Beating Landauer's Bound: Tradeoff between Accuracy and Heat Dissipation Saurav Talukdar, Shreyas Bhaban, Murti Salapaka The Landauer's Principle states that erasing of one bit of stored information is necessarily accompanied by heat dissipation of at least $k_{b} T\ln 2$per bit. However, this is true only if the erasure process is always successful. We demonstrate that if the erasure process has a success probability$ p$, the minimum heat dissipation per bit is given by $k_{b} T\left( {p\ln p+(1-p)\ln (1-p)+\ln 2} \right)$, referred to as the Generalized Landauer Bound, which is $k_{b} T\ln 2$if the erasure process is always successful and decreases to zero as $p$ reduces to 0.5. We present a model for a one-bit memory based on a Brownian particle in a double well potential motivated from optical tweezers and achieve erasure by manipulation of the optical fields. The method uniquely provides with a handle on the success proportion of the erasure. The thermodynamics framework for Langevin dynamics developed by Sekimoto is used for computation of heat dissipation in each realization of the erasure process. Using extensive Monte Carlo simulations, we demonstrate that the Landauer Bound of $k_{b} T\ln 2$is violated by compromising on the success of the erasure process, while validating the existence of the Generalized Landauer Bound. [Preview Abstract] |
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M1.00239: BIOLOGICAL PHYSICS |
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M1.00240: Cyto-molecular Tuning of Quantum Dots Bong Lee, Sindhuja Suresh, Andrew Ekpenyong Quantum dots (QDs) are semiconductor nanoparticles composed of groups II--VI or III--V elements, with physical dimensions smaller than the exciton Bohr radius, and between 1-10 nm. Their applications and promising myriad applications in photovoltaic cells, biomedical imaging, targeted drug delivery, quantum computing, etc, have led to much research on their interactions with other systems. For biological systems, research has focused on biocompatibility and cytotoxicity of QDs in the context of imaging/therapy. However, there is a paucity of work on how biological systems might be used to tune QDs. Here, we hypothesize that the photo-electronic properties of QDs can be tuned by biological macromolecules following controlled changes in cellular activities. Using CdSe/ZnS core-shell QDs, we perform spectroscopic analysis of optically excited colloidal QDs with and without promyelocytic HL60 cells. Preliminary results show shifts in the emission spectra of the colloidal dispersions with and without cells. We will present results for activated HL60-derived cells where specific macromolecules produced by these cells perturb the electric dipole moments of the excited QDs and the associated electric fields, in ways that constitute what we describe as cyto-molecular tuning. [Preview Abstract] |
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M1.00241: Real-Time Observation of Human LINE-1 Retrotransposon Activity in Bacteria Davneet Kaur, Thomas Kuhlman Transposable elements (TEs) are fundamental building blocks of all genomes. Retrotransposable elements (RTEs) are one of the two primary classes of TEs that are ubiquitous in eukaryotes. They propagate through a copy-and-paste mechanism utilizing reverse-transcribed mRNA intermediates. This leads to disruption and dispersal of coding and control elements throughout the genome, and consequently TEs are thought to be a major driving force behind diversification. However, RTEs are absent in most prokaryotes including E. coli. and the reason for this remains an open question. Despite their prevalence, there still remain many unanswered questions about how `hot' or active L1 RTEs (L1Hs) function. In particular, their rates of activity and their effects upon their host are currently poorly understood and only roughly estimated within the limitations of available technology. To address these unanswered questions, we have constructed and released an L1H element in E. coli to quantify its rates of activity and physiological effects on its host. To overcome the technical limitations, we've designed fluorescent visualization and quantification techniques that make real time high resolution observations of retrotransposition events as they occur in living cells. [Preview Abstract] |
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M1.00242: Neurofilament kinetics and changes in axonal caliber after axonal injury Tung Nguyen, Anthony Brown, Peter Jung Neurofilaments (NF) are the most abundant cytoskeletal structures in neuronal axons and determine their caliber. NFs are assembled in the cell body, and are also cargo of slow axonal transport moving distally at rate of 0.1 -- 1 mm/day. This dual role of NFs, as space filling structures and cargo of slow transport, im- plies a complex relation between axon caliber, NF influx from the cell body and transport kinetics, which is subject of our research. Changes in axon caliber, NF velocity, and NF flux observed after axonal injury, presents a good model system to study these complex relations. Axonal injury signals the cell body to reduce NF and tubulin influx, resulting in a wave of axon thinning, propagating distally at a rate consistent with NF velocity, while at the same time, NF transport rate is in- creasing. We developed a novel computational model for NF transport, where ac- cess of NFs to microtubule tracks and their organization determines their motility. Using this new computational model, we can relate the time-course of post-injury axonal thinning and increase of NF velocity by a reduction of NF flux and tubulin. The subsequent time - course of axonal recovery can be likewise associated with a recovery of NF flux and tubulin abundance. [Preview Abstract] |
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M1.00243: Stress-Strain Measurements of Semi-Aquatic Snake Lenses Nisha Lama, Dr. David Norwood, Dr. Cliff Fontenot, Addison Wallace, Mahitha Koduri, Dr. Rhett Allain It is of interest to understand the mechanism by which semi-aquatic maintain visual acuity when moving from land to underwater. Toward that end, we are interested in the mechanical properties of snake lenses and how this might affect the ability of snakes to deform the lens and thus alter the lens power. In this presentation, we will present data taken with a force sensor and a rotary motion sensor to measure, in one shot, force versus displacement, from which we estimate mechanical properties of stress and strain of the eye lens of a water snake. We will compare the results from lenses freshly removed from snake to those that have been stored. More importantly though, we will compare results from one species of semi-aquatic snakes to the other species of interest [Preview Abstract] |
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M1.00244: Optimal Pulse Configuration Design for Heart Stimulation. A Theoretical, Numerical and Experimental Study. Neil Hardy, Hila Dvir, Flavio Fenton Existing pacemakers consider the rectangular pulse to be the optimal form of stimulation current. However, other waveforms for the use of pacemakers could save energy while still stimulating the heart. We aim to find the optimal waveform for pacemaker use, and to offer a theoretical explanation for its advantage.~Since the pacemaker battery is a charge source, here we probe the stimulation current waveforms with respect to the total charge delivery. In this talk we present theoretical analysis and numerical simulations of myocyte ion-channel currents acting as an additional source of charge that adds to the external stimulating charge for stimulation purposes. Therefore, we find that as the action potential emerges, the external stimulating current can be reduced accordingly exponentially.~~We then performed experimental studies in rabbit and cat hearts and showed that indeed exponential truncated pulses with less total charge can still induce activation in the heart. From the experiments, we present curves showing the savings in charge as a function of exponential waveform and we calculated that the~longevity~of the pacemaker battery would be ten times higher for the exponential current compared to the rectangular waveforms. [Preview Abstract] |
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M1.00245: The Self-Assembly of DNA Nanostructures for use as Organizing Templates Timothy Samec, Mitchell Cholewinski, Nickalas Reamer, Michael Reardon, Arlene Ford There is growing interest in the self-assembling capabilities of DNA to create functional nanodevices for use in cancer detection and treatment. One important reason for this interest is that DNA nanostructures are highly programmable molecules. This means that these structures allow for increased stability and control when designing biomacromolecules via adhesion of plasmonic nanoparticles and other similar materials. Our current work reports on the procedure and construction of hexagonal two-dimensional DNA lattice structures using three specific DNA single strands. We also reflect on several barriers that were presented during fabrication as well as the adaptations made to overcome the aforementioned barriers by improving the quality, reproducibility, and yield of the hexagonal two-dimensional DNA lattice as organizing templates. [Preview Abstract] |
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M1.00246: Emergent Structures in an Active Polar Fluid: Dynamics of Shape, Scattering and Merger Kabir Husain, Madan Rao Spatially localised defect structures emerge spontaneously in a hydrodynamic description of an active polar fluid comprising polar 'actin' filaments and 'myosin' motor proteins that (un)bind to filaments and exert active contractile stresses. These emergent defect structures are characterized by distinct textures and can be either static or mobile - we derive effective equations of motion for these 'extended particles' and analyse their shape, kinetics, interactions and scattering. Depending on the impact parameter and propulsion speed, these active defects undergo elastic scattering or merger. Our results are relevant for the dynamics of actomyosin-dense structures at the cell cortex, reconstituted actomyosin complexes and 2D active colloidal gels. [Preview Abstract] |
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M1.00247: Influence of pore charge, pressure, and electric field on protein transport through nanopores. Meni Wanunu Nanopores are miniaturized electrical sensors with arguably the smallest detection volumes (sub-yoctometers, or below 10\textasciicircum -24 m\textasciicircum 3). Detection of molecules using nanopores involves electrical monitoring of ion current flow through a pore using a pair of electrodes placed across the nanopore-containing membrane. In such small confinements, the presence of electric field and a dominant surface area impose various conditions that must be taken into account when considering polymer translocation. this talk, I will describe how nanopores less than 10 nm in all dimensions (diameter and thickness) can be used to detect protein molecules at high resolution. I will discuss measurements of the surface charge of these nanopores, its role on the transport process, as well as the role of pressure on the sensitivity to protein transport detection. [Preview Abstract] |
(Author Not Attending)
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M1.00248: Towards multistage algorithm to model intrinsically unstructured proteins Antti Niemi, Jiaojiao Liu, Jin Dai, Jianfeng He, Nevena Ilieva We combine Landau mean field theory with all atom molecular dynamics into a multistage algorithm that can model protein folding and dynamics over very long time periods yet with atomic level precision. We propose that the approach is particularly suited to characterise the conformational states of intrinsically unstructured proteins. As an example we investigate an isolated monomeric Myc oncoprotein that has been implicated in many cancers. Under physiological conditions Myc is presumed to be an intrinsically disordered protein. Here we propose that room temperature Myc may have a stable folded conformation which we identify. For this we first use a Landau model investigation to confirm that as a monomer Myc is unstable, and uncover a highly degenerate structural landscape. We analyse its thermal stability properties using all atom molecular dynamics and observe a cluster of structures, with the two helical segments of the original leucine zipper aligned in parallel to each other. The cluster appears stable under room temperature all atom molecular dynamics simulations. During its stabilisation we identify a quasiparticle oscillation which is akin Davydov's Amide-I soliton, that fades away by diffusion. [Preview Abstract] |
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M1.00249: Monitoring single protease activities on triple-helical collagen molecules Raj Harzar, James Froberg, D. K. Srivastava, Yongki Choi Matrix metalloproteinases (MMPs), a particular family of proteases, play a pivotal role in degrading the extracellular matrix (ECM). It has been known for more than 40 years that MMPs are closely involved in multiple human cancers during cell growth, invasion, and metastasis. However, the mechanisms of MMP activity are far from being understood. Here, we monitored enzymatic processing of MMPs with two complementary approaches, atomic force microscopy and nanocircuits measurements. AFM measurements demonstrated that incubation of collagen monomers with MMPs resulted in a single position cleavage, producing 3/4 and 1/4 collagen fragments. From electronic monitoring of single MMP nanocircuit measurements, we were able to capture a single cleavage event with a rate of 0.012 Hz, which were in good agreement with fluorescence assay measurements. [Preview Abstract] |
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M1.00250: Statistical Mechanics of Protein Multimerization and Aggregation Kyle Hagner, Sima Setayeshgar, Michael Lynch, Paul Higgs Understanding the evolution of proteins is vital to explaining the diversification of life. As a majority of cellular proteins function not in isolation, but as part of complexes of two or more proteins, developing an understanding of how these protein- protein interactions originate and evolve is crucial. One intriguing observation is that highly-conserved proteins can exhibit different quaternary structures in different lineages, with no apparent correlation between the number of subunits in a complex and organismal complexity. In this work, we develop a theoretical model to investigate the aggregation of proteins on a cubic lattice using an hydrophobic-polar (HP) model. As most protein complexes are homomeric, composed of subunits derived from the same genetic locus, we focus on aggregates of multiple copies of the same protein as a function of concentration and the free energy of protein-protein binding. We construct a fitness landscape to investigate evolutionary trends by categorizing assemblies as monomers, isologous dimers, heterologous dimers, and higher-order assemblies, each with a corresponding impact on cellular fitness. [Preview Abstract] |
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M1.00251: A technique for studying cardiac myosin dynamics using optical tweezers Michael Paolino, Sam Migirditch, Yuri Nesmelov, Brooke Hester A primary protein involved in human muscle contraction is myosin, which exists in $\alpha $- and $\beta $- isoforms. Myosin exerts forces on actin filaments when ATP is present, driving muscle contraction. A significant decrease in the population of cardiac $\alpha $-myosin has been linked to heart failure. It is proposed that slow $\beta $-myosin in a failing heart could, through introduction of a drug, be made to mimic the action of $\alpha $-myosin, thereby improving cardiac muscle performance. In working towards testing this hypothesis, the focus of this work is to develop a technique to measure forces exerted by myosin on actin using optical tweezers. An actin-myosin arrangement is constructed between two optically trapped polystyrene microspheres. The displacement of a microsphere is monitored when ATP is introduced, and the force responsible is measured. With this achieved, we can then modify the actin-myosin arrangement, for example with varying amounts of $\alpha $- and $\beta $- myosin and test the effects on forces exerted. In this work, assemblies of actin and myosin molecules and preliminary force measurements are discussed. [Preview Abstract] |
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M1.00252: Mutation Induced Conformational Change In CaMKII Peptide Alters Binding Affinity to CaM Through Alternate Binding Site Jacob Ezerski, Margaret Cheung CaM forms distinct conformation states through modifications in its charge distribution upon binding to Ca$^{\mathrm{2+}}$ ions. The occurrence of protein structural change resulting from an altered charge distribution is paramount in the scheme of cellular signaling. Not only is charge induced structural change observed in CaM, it is also seen in an essential binding target: calmodulin-depended protein kinase II (CaMKII). In order to investigate the mechanism of selectivity in relation to changes in secondary structure, the CaM binding domain of CaMKII is isolated. Experimentally, charged residues of the CaMKII peptide are systematically mutated to alanine, resulting in altered binding kinetics between the peptide and the Ca$^{\mathrm{2+}}$ saturated state of CaM. We perform an all atom simulation of the wildtype (RRK) and mutated (AAA) CaMKII peptides and generate structures from the trajectory. We analyze RRK and AAA using DSSP and find significant structural differences due to the mutation. Structures from the RRK and AAA ensembles are then selected and docked onto the crystal structure of Ca$^{\mathrm{2+}}$ saturated CaM. We observe that RRK binds to CaM at the C-terminus, whereas the 3-residue mutation, AAA, shows increased patterns of binding to the N-terminus and linker regions of CaM. Due to the conformational change of the peptide ensemble from charged residue mutation, a distinct change in the binding site can be seen, which offers an explanation to experimentally observed changes in kinetic binding rates [Preview Abstract] |
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M1.00253: Universal hydrodynamic mechanisms for crystallization in active colloidal suspensions Rajesh Singh, R. Adhikari We derive, using the boundary integral formulation of Stokes flow, exact expressions for forces and torques between active colloidal particles near a plane wall. From the leading terms of these expressions we identify universal mechanisms for the crystallization of active colloids. Through detailed simulations, we find that active crystallization is not an activated process, as in equilibrium, but proceeds through a spinodal-like instability [1]. [1] Rajesh Singh and R. Adhikari, arXiv:1610.06528: To appear in Physical Review Letters [Preview Abstract] |
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M1.00254: Axonal Actin Transport Driven By Metastable Actin Filaments Nilaj Chakrabarty, Archan Ganguly, Subhojit Roy, Peter Jung Actin is one of the key constituents of the neuronal cytoskeleton and is responsible for driving important cellular processes like axon elongation. Axonal actin is synthesized in the cell body and transported at rates of 0.25 $-$ 3 mm/day, as shown by in-vivo pulse-chase radiolabelling studies. However, the underlying transport mechanisms are unknown. Recent experiments in cultured neurons have revealed a dynamic network of metastable actin filaments (“actin trails”). Actin trails seem to originate from focal actin “hotspots” which colocalize with stationary endosomes. Interestingly, the number of actin trails extending anterogradely is higher than the ones extending retrogradely. We hypothesize that the bulk axonal transport of actin originates from this directional asymmetry of the number of actin trails. To test this, we constructed a computational model of actin trail growth and simulated the pulse-chase experiment. In our model, local, metastable trails, which grow with their barbed ends anchored to the hotspots, drive the bulk anterograde transport. Our results indicate that the observed bias of the nucleation probabilities and the elongation rate of actin trails are sufficient to drive the bulk transport of actin at rates that agree with in-vivo pulse chase experiments. [Preview Abstract] |
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M1.00255: Microscale force response and morphology of tunable co-polymerized cytoskeleton networks Shea Ricketts, Vikrant Yadav, Jennifer L. Ross, Rae M. Robertson-Anderson The cytoskeleton is largely comprised of actin and microtubules that entangle and crosslink to form complex networks and structures, giving rise to nonlinear multifunctional mechanics in cells. The relative concentrations of semiflexible actin filaments and rigid microtubules tune cytoskeleton function, allowing cells to move and divide while maintaining rigidity and resilience. To elucidate this complex tunability, we create in vitro composites of co-polymerized actin and microtubules with actin:microtubule molar ratios of 0:1-1:0. We use optical tweezers and confocal microscopy to characterize the nonlinear microscale force response and morphology of the composites. We optically drag a microsphere 30 $\mu$m through varying actin-microtubule networks at 10 $\mu$m/s and 20 $\mu$m/s, and measure the force the networks exerts to resist the strain and the force relaxation following strain. We use dual-color confocal microscopy to image distinctly-labeled filaments in the networks, and characterize the integration of actin and microtubules, network connectivity, and filament rigidity. We find that increasing the fraction of microtubules in networks non-monotonically increases elasticity and stiffness, and hinders force relaxation by suppressing network mobility and fluctuations. [Preview Abstract] |
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M1.00256: Oscillations contribute to memory consolidation by changing criticality and stability in the brain Jiaxing Wu, Quinton Skilling, Nicolette Ognjanovski, Sara Aton, Michal Zochowski Oscillations are a universal feature of every level of brain dynamics and have been shown to contribute to many brain functions. To investigate the fundamental mechanism underpinning oscillatory activity, the properties of heterogeneous networks are compared in situations with and without oscillations. Our results show that both network criticality and stability are changed in the presence of oscillations. Criticality describes the network state of neuronal avalanche, a cascade of bursts of action potential firing in neural network. Stability measures how stable the spike timing relationship between neuron pairs is over time. Using a detailed spiking model, we found that the branching parameter $\sigma $ changes relative to oscillation and structural network properties, corresponding to transmission among different critical states. Also, analysis of functional network structures shows that the oscillation helps to stabilize neuronal representation of memory. Further, quantitatively similar results are observed in biological data recorded in vivo. In summary, we have observed that, by regulating the neuronal firing pattern, oscillations affect both criticality and stability properties of the network, and thus contribute to memory formation. [Preview Abstract] |
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M1.00257: Non-normal dynamics and positive feedback between motion and sensation boosts run-and-tumble navigation. Junjiajia Long, Steven W. Zucker, Thierry Emonet The capability to navigate environmental gradients is of critical importance for survival. Countless organisms (microbes, human cells, worms, larvae, and insects) as well as human-made robots use a run-and-tumble strategy to do so. The classical drawback of this approach is that runs in the wrong direction are wasteful. We show analytically that organisms can overcome this fundamental limitation by exploiting the non-normal dynamics and intrinsic nonlinearities inherent to the positive feedback between motion and sensation. Most importantly, this nonlinear amplification is asymmetric, elongating runs in favorable directions and abbreviating others. The result is a ``ratchet-like'' gradient climbing behavior with drift speeds that can approach half the maximum run speed of the organism. By extending the theoretical study of run-and-tumble navigation into the non-mean-field, nonlinear, and non-normal domains, our results provide a new level of understanding about this basic strategy. [Preview Abstract] |
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M1.00258: Nanotomography of brain networks Rino Saiga, Ryuta Mizutani, Susumu Takekoshi, Motoki Osawa, Makoto Arai, Akihisa Takeuchi, Kentaro Uesugi, Yasuko Terada, Yoshio Suzuki, Vincent De Andrade, Francesco De Carlo The first step to understanding how the brain functions is to analyze its 3D network. The brain network consists of neurons having micrometer to nanometer sized structures. Therefore, 3D analysis of brain tissue at the relevant resolution is essential for elucidating brain's functional mechanisms. Here, we report 3D structures of human and fly brain networks revealed with synchrotron radiation nanotomography, or nano-CT. Neurons were stained with high-Z elements to visualize their structures with X-rays. Nano-CT experiments were then performed at the 32-ID beamline of the Advanced Photon Source, Argonne National Laboratory and at the BL37XU and BL47XU beamlines of SPring-8. Reconstructed 3D images illustrated precise structures of human neurons, including dendritic spines responsible for synaptic connections. The network of the fly brain hemisphere was traced to build a skeletonized wire model. An article reviewing our study appeared in \underline {MIT Technology Review}. Movies of the obtained structures can be found in our \underline {YouTube channel}. [Preview Abstract] |
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M1.00259: Comparative Study of Bacterial Growth in Magnet Fields Jeffrey Gale, Samantha Gale, Samina Masood It is now well-known that magnetic fields affect bacterial growth. A comparative study of the growth rate for \textit{Escherichia coli K-12 }bacteria under the effect of different types of magnetic fields was done. Lysogenic broth was used at room temperature and the bacterial growth rates were studied in various magnetic fields including the electromagnetic field generated by a stack of Helmholtz coils. The growth rates were observed to identify the viability of the bacteria under applied magnetic field conditions. [Preview Abstract] |
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M1.00260: The Plasma Membrane is Compartmentalized by a Self-Similar Cortical Actin Fractal Sanaz Sadegh, Jenny Higgin, Patrick Mannion, Michael Tamkun, Diego Krapf A broad range of membrane proteins display anomalous diffusion on the cell surface. Different methods provide evidence for obstructed subdiffusion and diffusion on a fractal space, but the underlying structure inducing anomalous diffusion has never been visualized due to experimental challenges. We addressed this problem by imaging the cortical actin at high resolution while simultaneously tracking individual membrane proteins in live mammalian cells. Our data show that actin introduces barriers leading to compartmentalization of the plasma membrane and that membrane proteins are transiently confined within actin fences. Furthermore, superresolution imaging shows that the cortical actin is organized into a self-similar fractal. These results present a hierarchical nanoscale picture of the plasma membrane and demonstrate direct interactions between the actin cortex and the cell surface. [Preview Abstract] |
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M1.00261: The effect of electrostatic energy in determining the stable configuration and handedness of small-ring-DNA in the absence and presence of protein. Seyed Ahmad Sabok-Sayr, Wilma Olson We studied the electrostatic energy stored in a small-ring-DNA while its configuration changes over the in-plane normal mode. Our result shows that the normalized energy of the configuration increases as the number of base pairs increases but the normalized energy starts saturating above 500 base pairs. It may suggest where a circular DNA with enough base pairs may form a supercoil. We also studied the energy related to the interaction between the circular DNA and a protein as the DNA forms a supercoil with one complete turn around the protein. We found a synergy between the configuration of DNA and the position of the protein. Our studies show that the DNA forms a more stable configuration when the protein is outside the ring. We determined that the handedness of the protein will not change as it rotates from inside to outside of the small-ring-DNA and forms a $SO(3)$ group, while the handedness of DNA will change from right handed to left handed or vice versa as the protein transforms from the inside to the outside of the DNA and therefore this transformation in DNA forms a $O(3)$ group. [Preview Abstract] |
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M1.00262: Knotting and Unknotting Dynamics of DNA Strands in Nanochannels Antonio Suma, Enzo Orlandini, Cristian Micheletti Confinement of dsDNA in nanochannels can enhance or suppress altogether the strand’s knotting probability, affecting their metric, mechanical properties and interfering with the elongation process in nanofuidics devices. We characterize, through Langevin dynamic simulations, how knottedness arise from the internal dynamics of the chain, recovering the well characterized equilibrium knotting probability. Different channel widths are considered, covering various metric scaling regimes from 50 to 300 nm \footnote{C. Micheletti and E. Orlandini. \textbf{ACS Macro Lett} 3.9 (2014): 876-880.}, and different DNA lengths, from 1.2 to 4.8 nm \footnote{A. Suma, E. Orlandini and C. Micheletti. \textbf{J. Phys. Condens. Matter} 27.35 (2015): 354102.}. We explain the interplay between knot and unknot lifetimes and the channel and DNA parameters, relating these quantities to the equilibrium knotting probability. We show the basic knotting mechanism, which involves deep looping and back-foldings of the chain ends. The results can aid the design of nanochannels capable of harnessing the self-knotting dynamics to quench or relax the DNA topological state as desired. [Preview Abstract] |
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M1.00263: Knotted polymers in nanopores: static and dynamical properties Antonio Suma, Cristian Micheletti Knots arise spontaneously in sufficiently long polymers, especially when they are densely packed due to spatial confinement. We report here on a theoretical and computational characterization of model DNA chains confined in nanochannels. We will first focus on the equilibrium knotting probability and then report on the dynamical mechanisms through which knots are spontaneously formed and eventually untied in the confined chains~\footnote{A. Suma, E. Orlandini and C. Micheletti. \textit{J. Phys. Condens. Matter} 27.35 (2015): 354102.}. The case of knotted polymers chains translocating through narrow pores will also be discussed~\footnote{ A.Suma, A. Rosa and C. Micheletti. \textit{ACS Macro Letters}, 2015, 4(12), 1420-1424.}. [Preview Abstract] |
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M1.00264: Nanoscale lateral displacement arrays for the separation of exosomes and colloids down to 20 nm Robert Austin, Benjamin Wunsch, Joshua Smith, Stacey Gifford, Chao Wang, Markus Brink, Robert Bruce, Gustavo Stolovitzky, Yann Astier Deterministic lateral displacement (DLD) pillar arrays are an efficient technology to sort, separate and enrich micrometre-scale particles, which include parasites1, bacteria2, blood cells3 and circulating tumour cells in blood4. However, this technology has not been translated to the true nanoscale, where it could function on biocolloids, such as exosomes. Exosomes, a key target of ‘liquid biopsies’, are secreted by cells and contain nucleic acid and protein information about their originating tissue5. One challenge in the study of exosome biology is to sort exosomes by size and surface markers6, 7. We use manufacturable silicon processes to produce nanoscale DLD (nano-DLD) arrays of uniform gap sizes ranging from 25 to 235 nm. We show that at low Péclet (Pe) numbers, at which diffusion and deterministic displacement compete, nano-DLD arrays separate particles between 20 to 110 nm based on size with sharp resolution. Further, we demonstrate the size-based displacement of exosomes, and so open up the potential for on-chip sorting and quantification of these important biocolloids. [Preview Abstract] |
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M1.00265: Effect of Hind-Limb Suspension and X-Ray Irradiation on the Mechanical and Chemical Properties of Rat Femur and Tibia Bones Hayley Heacox, Brent Hill, Rahul Mehta, Jordan Barajas, Sidney Freyaldenhoven, Max Dobretsov, Parimal Chowdhury It is known that space conditions such as microgravity and cosmic radiation have detrimental effects on the skeletal system of humans, such as decreased bone mineral density. This research studies the changes in mechanical properties, elasticity, and chemical properties, calcium and phosphorus content, of rat femur and tibia bones when exposed to hind-limb suspension and x-ray irradiation, simulated microgravity and cosmic radiation. It is hypothesized that if microgravity and cosmic radiation lead to decreased bone mineral density, then these conditions will produce weakened bones, lower elastic moduli and abnormal concentrations of calcium and phosphorus, as compared to bones not subject to these conditions. A technique known as three-point bending was employed to estimate the Young's (elastic) modulus for the leg bones. To investigate the chemical nature of the bones, a Scanning Electron Microscope (SEM) was utilized to take cross-sectional images and to perform energy dispersive x-ray spectroscopy. Ultimately, the results produced by this research will aid in quantifying the effects of spaceflight and may be used in developing a treatment to counteract such effects. [Preview Abstract] |
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M1.00266: Surface plasmon resonance reflects diameter of actin structures decorated with gold nanorods Joel Solomon, Tejas Pruthi, Aaron Brettin, Vasily Astratov, Yuri Nesmelov We used actin filaments (diameter 6 nm [1]) and bundles (diameter 140 nm [1]), decorated with gold nanorods (AuNR, diameter 10 nm), to examine if the spectral position of surface plasmon resonance (SPR) follows diameter change of these biological objects. SPR is sensitive to the dielectric properties of the environment of the AuNR. Since the diameter of an actin filament is comparable to the diameter of a AuNR and the diameter of a bundle is much larger, the environment of a bound AuNR is different which should modulate the spectral position of the SPR. We found that the spectral position of the transverse SPR remained virtually the same for decorated filaments and bundles. The position of the longitudinal SPR was red shifted by 20 nm with the increase of the diameter of the biological object. We conclude that the spectral position of the longitudinal SPR reflects the difference in diameters of actin filaments and actin bundles upon decorating them with AuNR. [1] S. Jansen, A. Collins, C. Yang, G. Rebowski, T. Svitkina, and R. Dominguez. Mechanism of actin filament bundling by fascin. \textit{Journal of Biological Chemistry}, 286(34):30087-30096, 2011. [Preview Abstract] |
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M1.00267: Directive Nanophysical Cues for Regenerative Neural Cell Systems Virginia Ayres, Volkan Mujdat Tiryaki, Ijaz Ahmed, David Shreiber Until recently, implantables such as stents, probes, wafers and scaffolds have been viewed as passive vehicles for the delivery of physical, pharmacological and cellular interventions. Recent research, however, indicates that the physical environments that implantables present supply directive cues in their own right that work in conjunction with biochemical cues and produce a jointly-directed outcome. We will present our research in CNS repairs using advanced scanning probe microscopy, electron microscopies and contact angle measurements to quantitatively describe the nanoscale elasticity, surface roughness, work of adhesion and surface polarity for investigation of scaffold environments. We will also present our research using super-resolution immunocytochemistry and atomic force microscopy to evaluate neural cell morphological responses with associated micro filament, microtubule and intermediate filament expressions, along with results on how and which integrin-family receptors are possibly involved. Finally, we will present our novel application of k-means cluster analysis applied across multiple experimental modalities for quantification of synergistic scaffold properties and cell responses. [Preview Abstract] |
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M1.00268: Membrane-Mediated Self-Assemblies of Spherical Nanoparticles Eric J. Spangler, P.B. Sunil Kumar, Mohamed Laradji The understanding of membrane-mediated interactions between nanoparticles and their resulting aggregation is important to the use of nanomaterials in biomedical applications, their potential nanotoxic effects, and possibly for the use of biomembranes as a two-dimensional medium for the self-assembly of nanoparticles into structures that might be difficult to achieve otherwise. Using coarse-grained molecular dynamics simulations, we investigated the self-assembly of spherical nanoparticles on tensionless lipid membranes [1,2]. We found that the nanoparticles aggregate into a variety of structures that depend strongly on the nanoparticle-lipid adhesion interaction, nanoparticle diameter, and size of nanoparticles aggregates. The sequence of structures observed, with increasing the nanoparticle-lipid interaction strength, corresponds to linear chains, trenches, rings, and tubes. We also found that decreasing the number of particles depresses clustering of the nanoparticles, an indication the nature of membrane-mediated aggregation of nanoparticles is highly cooperative. [1] M. Laradji, P.B. Sunil Kumar, and E.J. Spangler, J. Phys. D: Appl. Phys. \textbf{49}, 293001 (2016) [2] E.J. Spangler, S. Upreti, and M. Laradji, J. Chem. Phys. \textbf{144}, 044901 (2016) [Preview Abstract] |
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M1.00269: Binding, Curvature-Sensing, Curvature-Generation and Self-Assembly of Anisotropically Curved Nanoparticles on Lipid Membranes Alexander D. Olinger, P.B. Sunil Kumar, Mohamed Laradji Golgi and endoplasmic reticulum in eukaryotic cells, owe their complex membrane conformations to specialized proteins known as BAR domains. Using coarse-grained molecular dynamics simulations [1], we investigated the binding and aggregation of anisotropically curved nanoparticles (NPs), akin to BAR domains, to tubular and spherical lipid vesicles. The ability of a NP to bind to a tubular membrane depends on the NP-lipid interaction strength, mismatch between the curvature of the NP and the tubular membrane, and the N's arclength. We found that the minimum interaction strength required for a NP binding increases with increasing the mismatch between the curvatures of the NP and the tubular membrane or increasing the NP arclength. We also investigated the aggregation of these NPs on lipid vesicles and found that they self-assemble into chains or asters depending on the NPs curvature and NP-lipid interaction strength. In particular, chains form for low NP-curvature or NP-lipid interaction strength, while asters form for high NP-curvature or high NP-lipid interaction strength [1] M. Laradji, P.B. Sunil Kumar, and E.J. Spangler, J. Phys. D: Appl. Phys. \textbf{49}, 293001 (2016) [Preview Abstract] |
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M1.00270: Courtship display dynamics, iridescent structural color and nanostructural pattern formation in ocellated pheasants Suzanne Amador Kane, Roslyn Dakin, Rui Fang, Yabin Lu Peacocks court females by tilting a fan-like array of feathers decorated with multicolored eyespots (ocelli). Previous research has shown that half of the variation in peacock mating success can be attributed to eyespot iridescence. Several closely-related pheasant species perform similar, but less complex, courtship displays using ocellated feathers with less complex coloration, patterns and underlying nanostructures. This study explores the relationship between the dynamics of male courtship behavior and optical properties and nanostructure of each species' iridescent feather ornaments. In particular, we examined videos of courting males and of individual feathers to measure how the angles used during displays compared to those corresponding to optimal eyespot reflected intensity and iridescent contrast. Bidirectional reflectance spectroscopy was used to measure how the spectrum of reflected light depends on the characteristic angles used during displays, and hence how displays stimulate the four classes of cones found in the color vision systems of these birds. This work reveals a close correlation between the complexity of the angular dependence of iridescent feather reflectance properties and that of the motions used by males of each species. [Preview Abstract] |
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M1.00271: Developmental Shape Transition in Cowrie Seashells Michael Levy, George Oster Cowries are a family of sea snail -- prevalent off the coast of Africa, in the Indian Ocean, and in the Pacific -- that undergoes a transition from laying shell down in a typical seashell spiral to spiraling inward and thickening the shell en route to maturity. This developmental path involves the formation of teeth-like ridges on the underside of the shell. Here we present modeling work that builds on the physics of wrinkling elastic sheets and mathematical approaches to the form and development of seashells to provide an avenue towards understanding the process underlying this transition. We also present experimental data on the link between geometry of the shell and material coupling of soft-body mantle growth and shell deposition. Our calculations, based on elasticity theory and geometry, link a behavioral change in the lifecycle of the mollusc to this under-studied shape transition. Coupling mechanics to shell repair mechanisms and development provides a physical understanding of the emergent structure of Cowrie shells. [Preview Abstract] |
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M1.00272: Rapid emergence and mechanisms of resistance by U87 glioblastoma cells to doxorubicin in an in vitro tumor microfluidic ecology Robert Austin, Sanghyuk Lee, Sungsu Park We have developed a microfluidic device consisting of approximately 500 hexagonal micro-compartments which provides a complex ecology with wide ranges of drug and nutrient gradients and local populations. This ecology of a fragmented metapopulation induced the drug resistance in stage IV U87 glioblastoma cells to doxorubicin in seven days. Exome and transcriptome sequencing of the resistant cells identified mutations and differentially expressed genes. Gene ontology and pathway analyses of the genes identified showed that they were functionally relevant with the established mechanisms of doxorubicin action. Functional experiments support the in silico analyses and together demonstrate the effects of these genetic changes. Our findings suggest that given the rapid evolution of resistance and the focused response, this technology could act as a rapid screening modality for genetic aberrations leading to resistance to chemotherapy as well as counter-selection of drugs unlikely to be successful ultimately. [Preview Abstract] |
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M1.00273: Active turnover regulates pattern formation and stress transmission in disordered acto-myosin networks Patrick McCall, Samantha Stam, David Kovar, Margaret Gardel The shape and mechanics of animal cells are controlled by a dynamic, thin network of semiflexible actin filaments and myosin-II motor proteins called the actomyosin cortex. Motor-generated stresses in the cortex drive changes in cell shape during cell division and morphogenesis, while dynamic turnover of actin filaments dissipates stress. The relative effects that force generation, force dissipation, and disassembly and reassembly of material have on motion in these networks are unknown. We find that cross-linked actin networks in vitro contract under myosin-generated stresses, resulting in partial filament disassembly, the formation of asters, and clustering of myosin motors. We observe a rapid restoration of uniform polymer density in the presence of the assembly factors which catalyze network turnover through elongation of severed actin filaments. When severing is accelerated further by the addition of a severing protein, network contraction and motor clustering are dramatically suppressed. We test the relative effects of material regeneration and force transmission using image analysis, and conclude that the dominant mechanism for this effect is relatively short-lived stresses that do not propagate over considerable distance or push network deformation into the nonlinear contractile regime we have previously characterized. Our results present a framework to understand cytoskeletal active matter that are influenced by a complex interplay between stress generation, network reorganization, and polymer turnover. [Preview Abstract] |
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M1.00274: Manifold-embedding methods for extracting continuous conformational ensembles of biological molecules from single-particle measurements using X-ray Free Electron Lasers. Jeremy Copperman, Ahmad Hosseinizadeh, Ghoncheh Mashayekhi, Peter Schwander, Ali Dashti, Russell Fung, Abbas Ourmazd A novel machine-learning approach allows us to navigate the high-dimensional space of single-particle XFEL scattering data. This technique can be used to map continuous conformational changes in biological systems, and to determine the energy landscape associated with such changes. With the extremely large datasets expected from high repetition-rate XFELs about to enter service, this approach promises unprecedented access to rare, rate-limiting conformations energetically far above the thermal bath. [Preview Abstract] |
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M1.00275: A Comparison of the Viscosities of Thickened Liquids for Pediatric Dysphagia. Ranjith Wijesinghe, Mekale Clifton, Morgan Tarlton, Erica Heinsohn, Mary Ewing It has been reported that Speech Language Pathologists in different facilities across the nation use a variety of thickening agents and recipes as therapeutic measures for infants and children diagnosed with dysphagia. Limited research has been completed in this area. Viscosity was tested to determine the thickness of each thickening agent mixed with infant formula. The values were then compared to the National Dysphagia Diet liquid levels to determine which thickening agent resulted in the desired viscosity levels. The thickeners were mixed with common infant formulas and soy formulas to determine if the type of formula impacted the viscosity. The main goal was to determine if the assumed thickness level (viscosity) of prescribed thickened liquids was actually being met. This topic is of high concern because of its impact on the safety and well-being of clients with dysphagia. A viscometer was used to collect the viscosity levels. Commercially available formulas selected for this study. The final results of our investigation will be presented during the APS meeting. [Preview Abstract] |
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M1.00276: Phase segregation in the Active Composite Cell Surface: clustering and sorting of cell surface molecules at different scales Amit Das, Suvrajit Saha, Madan Rao, Satyajit Mayor Several studies have shown that a variety of cell surface molecules, e.g. GPI-anchored proteins, ras-signalling proteins and many transmembrane receptors, form dynamic nanoclusters driven by actomyosin flows at the cell-cortex. We now ask whether these different species of molecules exhibit a larger scale segregation, depending on their relative binding affinities to actin. Using an effective coarse-grained theory which describes the dynamics of localized contractile platforms or asters, we show that two species of molecules with widely differing binding affinities to actin, segregate over large scales, even at temperatures larger than the equilibrium phase segregation temperature of the binary system. The kinetics of segregation and the statistics of this actively segregated state are dramatically different from its equilibrium counterpart. The kinetics is slow, and shows a breakdown of Porod behaviour, indicating that the segregated domains have low interfacial tension. The domains exhibit macroscopic and intermittent fluctuations at steady state, characteristic of fluctuation dominated phase ordering. At temperatures below equilibrium ordering, activity results in a breakdown of large domains. Many of these predictions are being tested by in-vitro experiments. [Preview Abstract] |
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M1.00277: Molecular Dynamics of the ZIKA Virus NS3 Helicase Bryan Raubenolt, Steven Rick The recent outbreaks of the ZIKA virus (ZIKV) and its connection to microcephaly in newborns has raised its awareness as a global threat and many scientific research efforts are currently underway in attempt to create a vaccine. Molecular Dynamics is a powerful method of investigating the physical behavior of protein complexes. ZIKV is comprised of 3 structural and 7 nonstructural proteins. The NS3 helicase protein appears to play a significant role in the replication complex and its inhibition could be a crucial source of antiviral drug design. This research primarily focuses on studying the structural dynamics, over the course of few hundred nanoseconds, of NS3 helicase in the free state, as well as in complex form with human ssRNA, ATP, and an analogue of GTP. RMSD and RMSF plots of each simulation will provide details on the forces involved in the overall stability of the active and inactive states. Furthermore, free energy calculations on a per residue level will reveal the most interactive residues between states and ultimately the primary driving force behind these interactions. Together these analyses will provide highly relevant information on the binding surface chemistry and thus serve as the basis for potential drug design. [Preview Abstract] |
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M1.00278: Infrared Structural Biology: A Tool for Probing Structure and Dynamics of Functional Histidines in Proteins Aihua Xie, Charle Liu, Matthew Cavener We report a method for structure-function studies of histidine in proteins based on signature infrared signals. The imidazole group of histidine residues are found functionally important in a vast number of catalytic proteins. Knowledge on the protonation states of key histidine side chains in enzymes at rest and during catalytic actions is indispensable to elucidation of the structure-function relationship underlying enzymatic catalysis. We report a rigorous method on how to detect the three protonation states of functionally important histidine imidazole rings in the static and dynamic states of enzymes using infrared structural biology. First principle computational methods based on density functional theory were employed to develop two vibrational structural markers (VSM) of the imidazole group: VSMq for the charged states of the imidazole group, while VSMt for distinguishing the D and E tautomers of charge neutral histidine. The accuracy of the VSMs is assessed by comparison of calculated VSMs with experimental FT-IR data of the 4-ethyl-imidazole model compound. We will discuss how these VSMs may be employed in structure-function studies on functionally important histidine residues in enzymes. [Preview Abstract] |
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M1.00279: Molecular Dynamics Study of the Solubility Curve of Polyglutamine for the PLUM Model. Songul Kutlu, Jason Haaga, James D. Gunton A recent study by Crick et al [1,2] determined the saturation (solubility) curve for polyglutamine (PolyQ) for several different repeat lengths, n, of Qn, and for different flanking sequences, such as K2. The degree of supersaturation S, (S$=$ln(Co/Ce), where Co and Ce are the metastable and equilibrium saturation monomer concentrations, respectively) plays a crucial role in the kinetics of aggregation of misfolded proteins containing polyQ. Thus the degree of supersaturation is an important factor in diseases such as Huntington's disease for which polyQ is a major component. We present here preliminary results of a molecular dynamics study for the solubility curve for a PLUM model of Q10. (An extensive study of the kinetics of aggregation for this model is being carried out in a separate study [3]) Our results display a normal solubility curve behavior, with the saturation concentration increasing with increasing temperature. This is only in partial qualitative agreement with the experimental results, which show a retrograde behavior at low temperatures. We are extending this study to other repeat lengths, including Q40. $\backslash \backslash $ $\backslash \backslash $1.~PhD Thesis, S. Crick, Jan~(2011), Washington University. 2. S.L. Crick,~K. M. Ruff,~K. Garai,~C. Frieden,~and~R. V. Pappu, PNAS~2013~110~(50)~ 20075-20080. 3. J. Haaga, C. N. Buckley and J. D. Gunton, unpublished (2016). [Preview Abstract] |
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M1.00280: Learning physical biology via modeling/simulation: An interdisciplinary undergraduate course Philip Nelson Undergraduate life-science curricula remain largely rooted in descriptive approaches, even though much current research involves quantitative modeling. Not only does our pedagogy not reflect current reality; it also reinforces the silos that prevent students from connecting disciplines. I'll describe a course that has attracted undergraduates in several science and engineering majors. Students acquire research skills that are often not addressed in traditional undergraduate courses, using a general-purpose platform like MATLAB or Python. The combination of experimental data, modeling, and physical reasoning used in this course represents an entirely new mode of "how to learn" for most of the students. These basic skills are presented in the context of case studies from cell biology, specifically control theory and its applications to synthetic biology. Documented outcomes include student reports of improved ability to gain research positions as undergraduates, and greater effectiveness in such positions, as well as students enrolling in more challenging later courses than they would otherwise have chosen. [Preview Abstract] |
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M1.00281: An adaptive molecular timer in p53-meidated cell fate decision Xiao-Peng Zhang, Ping Wang, Feng Liu, Wei Wang The tumor suppressor p53 decides cellular outcomes in the DNA damage response. It is intriguing to explore the link between p53 dynamics and cell fates. We developed a theoretical model of p53 signaling network to clarify the mechanism of cell fate decision mediated by its dynamics. We found that the interplay between p53-Mdm2 negative feedback loop and p53-PTEN-Mdm2 positive feedback loop shapes p53 dynamics. Depending on the intensity of DNA damage, p53 shows three modes of dynamics: persistent pulses, two-phase dynamics with pulses followed by sustained high levels and straightforward high levels. Especially, p53 shows two-phase dynamics upon moderated damage and the required number of p53 pulses before apoptosis induction decreases with increasing DNA damage. Our results suggested there exists an adaptive molecular timer that determines whether and when the apoptosis switch should be triggered. We clarified the mechanism behind the switching of p53 dynamical modes by bifurcation analysis. Moreover, we reproduced the experimental results that drug additions alter p53 pulses to sustained p53 activation and leads to senescence. Our work may advance the understanding the significance of p53 dynamics in tumor suppression. [Preview Abstract] |
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M1.00282: Encoding of natural and artificial stimuli in the auditory midbrain Dominika Lyzwa How complex acoustic stimuli are encoded in the main center of convergence in the auditory midbrain is not clear. Here, the representation of neural spiking responses to natural and artificial sounds across this subcortical structure is investigated based on neurophysiological recordings from the mammalian midbrain. Neural and stimulus correlations of neuronal pairs are analyzed with respect to the neurons' distance, and responses to different natural communication sounds are discriminated. A model which includes linear and nonlinear neural response properties of this nucleus is presented and employed to predict temporal spiking responses to new sounds. [Preview Abstract] |
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M1.00283: Cell heterogeneity and temporal heterogeneity determine single cell motility Tae Jin Kwon, Ok-Seon Kwon, Hyuk-Jin Cha, Bong June Sung Single cell migration plays an important role in cancer metastasis. It is, however, difficult to quantify the cell migration because single cell dynamics is significantly heterogeneous. Such a heterogeneity in cell migration may arise from two reasons:(1) the population of cancer cells consists of subpopulations of different motility (called cell heterogeneity) and/or (2) all cancer cells have the identical average motility but their motilities change temporally (called temporal heterogeneity). In this work, we perform a comparative study on each case with A549-shCont cell dynamics in two dimensions in the absence of external signals. We obtain cell trajectories by employing time-lapse microscopy. We compare the transport properties of cells with numerical simulations, which consider cell heterogeneity and/or temporal heterogeneity. We show that both cell heterogeneity and temporal heterogeneity need be taken into account to explain single cell behavior. [Preview Abstract] |
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M1.00284: Self-Assembly Kinetics of Nanoscale Fused $\beta$-Solenoid Protein Units Talia Sopp, Rachel Baarda, Daniel Cox $\beta$-solenoid protein (BSP) backbones twist helically to form coils of $\beta$-sheets. BSPs are mechanically robust, are easily customizable, and can self-assemble into complexes at room temperature. BSPs can be fused to small symmetric oligomers to create protein lattices with potential industrial applications ranging from synthetic antibodies to scaffolding nanomaterials. To assess the feasibility of creating such lattices, we modeled the formation of one of the simplest cases (a single hexagon) in \textit{E. coli}. The hexagon is composed of trimer subunits in which two of the monomers have BSPs fused to them; six of these subunits form a hexagon. We modeled the formation of these subunits in \textit{E. coli} as a series of diffusion-controlled reactions. We used two models to estimate the amount of this product and others over time: the deterministic reaction-rate theory and the stochastic Gillespie Method. Both showed that we could expect about 120 hexagon subunits to form in 15 minutes in one cell. We conclude that creating our hexagon BSP structure in \textit{E. coli} is feasible. Our results will inform the experimental production of the hexagonal BSP structure. Additionally, we can apply the simulation method we developed to more complex protein lattices. [Preview Abstract] |
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M1.00285: A Microfluidics Platform for Visualizing Single Molecule Dynamics in a Model Glycocalyx Dylan Young, Isabel Newsome, Jan Scrimgeour The glycocalyx of endothelial cells is a hyaluronan-rich polymer brush that extends from the endothelial surface into the blood vessel where it is involved in mechano-sensing, shear flow moderation and molecular filtering. The brush is formed by long hyaluronan molecules that is extruded through the cell membrane and the structure of the brush is manipulated by a diverse set of hyaluronan binding proteins. However, the low molecular density, high levels of hydration and complex flow environment about this structure has made it a difficult target for biophysical characterization. In this poster, we present a microfluidics platform that uses a linear voice coil actuator to modulate the flow through the system. This system is applied to study a model glycocalyx that is grafted to a hydrogel force sensor. This model system allows us to probe the dynamics of proteins in the model system using high-speed single molecule microscopy, while also enabling the strain on the hydrogel substrate to be measured as the composition of the brush is manipulated. [Preview Abstract] |
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M1.00286: Rate-equation modelling and ensemble approach to extraction of parameters for viral infection-induced cell apoptosis and necrosis. Sergii Domanskyi, Joshua Schilling, Vyacheslav Gorshkov, Sergiy Libert, Vladimir Privman We develop a theoretical approach that uses physiochemical kinetics modelling to describe cell population dynamics upon progression of viral infection in cell culture, which results in cell apoptosis (programmed cell death) and necrosis (direct cell death). Several model parameters necessary for computer simulation were determined by reviewing and analyzing available published experimental data. By comparing experimental data to computer modelling results, we identify the parameters that are the most sensitive to the measured system properties and allow for the best data fitting. Our model allows extraction of parameters from experimental data and also has predictive power. Using the model we describe interesting time-dependent quantities that were not directly measured in the experiment and identify correlations among the fitted parameter values. Numerical simulation of viral infection progression is done by a rate-equation approach resulting in a system of ``stiff'' equations, which are solved by using a novel variant of the stochastic ensemble modelling approach. The latter was originally developed for coupled chemical reactions. [Preview Abstract] |
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M1.00287: Cell vertices as independent actors during cell intercalation in epithelial morphogenesis Dinah Loerke Epithelial sheets form the lining of organ surfaces and body cavities, and it is now appreciated that these sheets are dynamic structures that can undergo significant reorganizing events, e.g. during wound healing or morphogenesis. One of the key morphogenetic mechanisms that is utilized during development is tissue elongation, which is driven by oriented cell intercalation. In the Drosophila embryonic epithelium, this occurs through the contraction of vertical T1 interfaces and the subsequent resolution of horizontal T3 interfaces (analogous to so-called T1 transitions in soap foams), where the symmetry breaking behaviors are created by a system of planar polarity of actomyosin and adhesion complexes within the cell layer. The dominant physical model for this process posits that the anisotropy of line tension directs T1 contraction. However, this model is inconsistent with the in vivo observation that cell vertices of T1 interfaces lack physical coupling, and instead show independent movements. Thus, we propose that a more useful explanation of intercalary behaviors will be possible through a description of the radially-directed and adhesion-coupled force events that lead to vertex movements and produce subsequent dependent changes in interface lengths. [Preview Abstract] |
(Author Not Attending)
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M1.00288: Statistical Modeling of an Optically Trapped Cilium Justin Flaherty, Andrew Resnick We explore, analytically and experimentally, the stochastic dynamics of a biologically significant slender microcantilever, the primary cilium, held within an optical trap. Primary cilia are cellular organelles, present on most vertebrate cells, hypothesized to function as a fluid flow sensor. The mechanical properties of a cilium remain incompletely characterized. Optical trapping is an ideal method to probe the mechanical response of a cilium due to the spatial localization and non-contact nature of the applied force. However, analysis of an optically trapped cilium is complicated both by the geometry of a cilium and boundary conditions. Here, we present experimentally measured mean-squared displacement data of trapped cilia where the trapping force is oppositely directed to the elastic restoring force of the ciliary axoneme, analytical modeling results deriving the mean-squared displacement of a trapped cilium using the Langevin approach, and apply our analytical results to the experimental data. We demonstrate that mechanical properties of the cilium can be accurately determined and efficiently extracted from the data using our model. It is hoped that improved measurements will result in deeper understanding of the biological function of cellular flow sensing by this organelle. [Preview Abstract] |
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M1.00289: Vision in dinosaurs: Scaling effects in sclerotic rings Scott Lee Sclerotic rings are composed of bones found in the eyes of most vertebrates except mammals and crocodilians. They are believed to have a role in maintaining the shape of the eye. Their inner diameter is an upper limit for the effective diameter of the pupil and, therefore, provides a measure of the light-gathering ability of the eyes of extinct animals. Thirty-six different species of dinosaurs (from both the Saurischian and Ornithischian branches) have been studied. The smallest dinosaurs, with masses less than 1 kg, include \textit{Juravenator starki}, \textit{Archaeopteryx lithographica}, and \textit{Mei long} while the largest dinosaurs, with masses on the order of 10,000 kg, include \textit{Diplodocus longus} and \textit{Nemegtosaurus mongoliensis}. The light-gathering properties of the eyes of the dinosaurs are studied as a function of the mass. The sclerotic ring diameter is found to increase with mass. [Preview Abstract] |
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M1.00290: Abstract Withdrawn
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M1.00291: Physics of the Brain. Prevention of the Epileptic Seizures by the Multi-photon Pulsed-operated Fiber Lasers in the Ultraviolet Range of Frequencies. V Alexander Stefan The novel study of the epileptogenesis mechanisms\footnote{ E.M. Goldberg and D.A Coulter, Nat. Rev. Neurosci.14(5), 337 (2013).} is proposed. It is based on the pulsed-operated (amplitude modulation) multi-photon (frequency modulation) fiber-laser interaction with the brain epilepsy-topion (the epilepsy onset area),\footnote{ V. Stefan, B. I. Cohen, C. Joshi, \textit{Science}, 243, 4890, (1989); Stefan et al., Bull. APS 32, No.9, 1713, (1987); Stefan, APS-March-2015, {\#} P1.00099;\textbf{~}Stefan, APS-March-2016, {\#}M1.00310;\textbf{~}V. Alexander Stefan, Neurophysics\textit{, Stem Cell Physics, and Genomic Physics: Beat-Wave-Driven-Free Electron Laser Beam Interactions with the Living Matter}, (S-U-Press, La Jolla, CA, 2012).\par } so as to prevent the excessive electrical discharge (epileptic seizure) in the brain. The repetition frequency, $\Omega $, matches the low frequency (epileptic) phonon waves in the brain. The laser repetition frequency (5-100 pulses per second) enables the resonance-scanning of the wide range of the phonon (possible epileptic-to-be) activity in the brain. The tunable fiber laser frequencies, $\Delta \omega $ (multi photon operation), are in the ultraviolet frequency range, thus enabling monitoring of the electrical charge imbalance (within the 10s of milliseconds), and the DNA-corruption in the epilepsy-topion, as the possible cause of the disease. [Preview Abstract] |
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M1.00292: Cooperation, collapse and resilience: ecological and evolutionary consequences of heterogeneous metapopulation structure Anurag Limdi, Alfonso Perez-Escudero, Aming Li, Jeff Gore While negative frequency and density dependent selection and population structure are used to explain the evolution of cooperation separately, their combined effect remains unexplored. Here, we consider the effect of heterogeneity of metapopulations linked by migration in a yeast cooperator-defector system. We discover that asymmetric migration on star networks, coupled with density dependent selection, can double the cooperator fraction compared to isolated nodes and fully connected networks. Migration reduces population density on the side nodes which makes star networks more prone to collapse in challenging environments than isolated populations. Unexpectedly, we find that star networks have greater resilience to a temporary salt shock than isolated nodes. This can be reconciled by noting that the level of permanent stress that the network can withstand is influenced by side nodes which are the most vulnerable parts of the network. In contrast, the ability to recover from temporary shocks is defined by the central node (which has a higher density and cooperator fraction than isolated nodes), because it can reseed the side nodes and rescue the whole network. Our findings highlight that ecological communities respond differently to constantly and transiently harsh environments. [Preview Abstract] |
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M1.00293: Correlation-based and model-based inference in complex virus-microbe communities Ashley R. Coenen, Joshua S. Weitz Microbes are found in high abundances in the environment and in human-associated microbiomes, often exceeding one million per milliliter. Viruses of microbes are estimated to turn over 10 to 40 percent of microbes daily and, consequently, are important in shaping microbial communities. Yet, the interactions among microbes and viruses are difficult to pin down \emph{in situ}. Deducing which pairs interact in complex virus-microbe communities (the ``inference problem'') remains an open question. Here, we test two approaches to the inference problem with \emph{in silico} experiments. The first approach uses correlations between population time series to indicate interaction. Contrary to widespread use, our results suggest that correlation is a poor indicator of interaction when interactions are not already known \emph{a priori}. The second approach extends recent work (Jover, Romberg, and Weitz, \emph{Roy Soc Open Science}, 2016) by discretizing a nonlinear mechanistic model to infer virus-microbe as well as microbe-microbe interactions. We find that, unlike the correlation-based approach, the model-based inference is robust to variation in network structure and life history traits. In addition, inference is possible even when microbe-microbe competition is heterogeneous. [Preview Abstract] |
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M1.00294: Burstiness in Viral Bursts: How Stochasticity Affects Spatial Patterns in Virus-Microbe Dynamics Yu-Hui Lin, Bradford P. Taylor, Joshua S. Weitz Spatial patterns emerge in living systems at the scale of microbes to metazoans. These patterns can be driven, in part, by the stochasticity inherent to the birth and death of individuals. For microbe-virus systems, infection and lysis of hosts by viruses results in both mortality of hosts and production of viral progeny. Here, we study how variation in the number of viral progeny per lysis event affects the spatial clustering of both viruses and microbes. Each viral "burst" is initially localized at a near-cellular scale. The number of progeny in a single lysis event can vary in magnitude between tens and thousands. These perturbations are not accounted for in mean-field models. Here we developed individual-based models to investigate how stochasticity affects spatial patterns in virus-microbe systems. We measured the spatial clustering of individuals using pair correlation functions. We found that increasing the burst size of viruses while maintaining the same production rate led to enhanced clustering. In this poster we also report on preliminary analysis on the evolution of the burstiness of viral bursts given a spatially distributed host community. [Preview Abstract] |
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M1.00295: Tracking C. elegans and its neuromuscular activity using NemaFlex II Frank Van Bussel, Mizanur Rahman, Jerzy Blawzdziewicz, Siva Vanapalli NemaFlex is a recently developed experimental platform designed to analyze the movement and muscular strength of crawling C. elegans. Physically it is a microfluidic device consisting of an array of deformable PDMS pillars, with which the C. elegans interacts in the course of moving through the system; image data is then acquired through a transparent top plate. The software component uses this image data to track the worm's movements and measure pillar deflections and thereby the forces exerted by the worm, in a fully automated, high-throughput manner. In order to correlate the force results with muscle activations the pillar deflections need to be precisely associated with mechanical contact on the worm's body, which requires accurate determination and representation of the body's position within the complex background. Here we discuss issues encountered in extracting this position data from the surrounding environment. [Preview Abstract] |
(Author Not Attending)
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M1.00296: Network analysis reveals the recognition mechanism for complex formation of mannose-binding lectins Yiren Jian, Yunjie Zhao, Chen Zeng The specific carbohydrate binding of lectin makes the protein a powerful molecular tool for various applications including cancer cell detection due to its glycoprotein profile on the cell surface. Most biologically active lectins are dimeric. To understand the structure-function relation of lectin complex, it is essential to elucidate the short- and long-range driving forces behind the dimer formation. Here we report our molecular dynamics simulations and associated dynamical network analysis on a particular lectin, i.e., the mannose-binding lectin from garlic. Our results, further supported by sequence coevolution analysis, shed light on how different parts of the complex communicate with each other. We propose a general framework for deciphering the recognition mechanism underlying protein-protein interactions that may have potential applications in signaling pathways. [Preview Abstract] |
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M1.00297: PHYSICS OF CLIMATE |
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M1.00298: Role of structural morphology in urban heat islands Thorsten Emig The urban heat island (UHI) is a common phenomenon in which air and surface temperatures are elevated in urban areas compared to surrounding rural areas. It has profound impact on the lives of urban residents (50{\%} of the world's population) and energy consumption. A traditional approach in studying the UHI is to consider relative small urban regions (single street canyons) for modeling the local climate. In this talk I report our studies of the correlations between the UHI intensity and urban morphology over large urban areas (6 miles diameter) for 22 US urban regions. The observations are explained in terms of heat radiation transfer models. I shall introduce a relative simple version of such models to describe the equilibrium surface temperatures of large areas of New York City at night time where the UHI intensity is largest. The agreement with large scale spectroscopic measurements of surface temperatures on the west side of Manhattan is reassuring. [Preview Abstract] |
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M1.00299: Computational designing and screening of solid materials for CO$_{\mathrm{\mathbf{2}}}$\textbf{ capture} Yuhua Duan In this presentation, we will update our progress on computational designing and screening of solid materials for CO$_{\mathrm{2}}$ capture. By combining thermodynamic database mining with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify the most promising CO$_{\mathrm{2}}$ sorbent candidates from the vast array of possible solid materials have been proposed and validated at NETL. The advantage of this method is that it identifies the thermodynamic properties of the CO$_{\mathrm{2}}$ capture reaction as a function of temperature and pressure without any experimental input beyond crystallographic structural information of the solid phases involved. The calculated thermodynamic properties of different classes of solid materials versus temperature and pressure changes were further used to evaluate the equilibrium properties for the CO$_{\mathrm{2}}$ adsorption/desorption cycles. According to the requirements imposed by the pre- and post- combustion technologies and based on our calculated thermodynamic properties for the CO$_{\mathrm{2}}$ capture reactions by the solids of interest, we were able to identify only those solid materials for which lower capture energy costs are expected at the desired working conditions. In addition, we present a simulation scheme to increase and decrease the turnover temperature (T$_{\mathrm{t}})$ of solid capturing CO$_{\mathrm{2}}$ reaction by mixing other solids. Our results also show that some solid sorbents can serve as bi-functional materials: CO$_{\mathrm{2}}$ sorbent and CO oxidation catalyst. Such dual functionality could be used for removing both CO and CO$_{\mathrm{2}}$ after water-gas-shift to obtain pure H$_{\mathrm{2}}$. [Preview Abstract] |
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M1.00300: INSTRUMENTATION AND MEASUREMENTS |
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M1.00301: Analysis of Outgassing Properties of Candidate Materials for Use With the nEXO Experiment Twymun Safford, Liang Yang The experimental search for neutrinoless double beta decay (0$\nu \beta \beta )$ is a test of the Majorana nature of neutrinos and the violation of lepton number. With some uncertainty, the rate of neutrinoless double beta decay is also proportional to the square of the effective Majorana neutrino mass. EXO-200 is an experiment designed to search for double beta decay of xenon-136 using a single-phase, liquid xenon detector. EXO-200 uses an active mass of 110 kilograms of liquid xenon-136 enriched to 80.6{\%} in an ultra-low background time projection chamber capable of simultaneous detection of ionization and scintillation. The University of Illinois at Urbana-Champaign collaborates with the EXO-200 experiment. During the summer at the University of Illinois at Urbana-Champaign, research was conducted by utilizing a vacuum chamber in tandem with a vacuum pump to analyze the outgassing properties of various candidate materials in terms of electronegative impurities for use with the future nEXO experiment. Materials such as kapton flexible connection cables were used. In the future, plans to construct a carbon nanotube-based adhesive will be executed to inexpensively simulate the behavior of parts used in the recirculation process of the liquid xenon. [Preview Abstract] |
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M1.00302: Correlating Wet-Sample Electron Microscopy with Light Scattering Spectroscopy on the Example of Polymeric Microgels. Christian Gunder, Petru S. Fodor, Kiril A. Streletzky Amphiphilic cellulose-based microgels with a reversible volume-phase transition at around 40.5$^{\circ}$ C (the low critical solution temperature (LCST)), have been synthesized, characterized, and optimized. The specific size dependence on the temperature exhibited by these microgels and their bio-compatibility makes them attractive systems for drug delivery and bio-sensing. In this work, in order to study the characteristics of their response under dynamic temperature conditions, both light scattering spectroscopy, as well as electron microscopy are used. While the light scattering data provides critical insights in regard to the size, shape, molecular weight and dynamics of the microgel particles investigated, the data obtained represents an average over the relatively large sample volume accessed by these optical techniques. Thus, the data interpretation can be greatly strengthened with supporting direct imaging measurements capable of monitoring individual particles with high spatial resolution, such as electron microscopy. To this end we develop methods enabling the electron imaging of microgel samples while maintaining their solution environment. In this context, one of the approaches that proved viable, is using a specially designed capsule in which the sample is sealed behind a thin SiN window that isolates the liquid sample from the electron column vacuum. We discuss the correlation of the imaging results obtained through these methods, with the data obtained from light scattering. [Preview Abstract] |
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M1.00303: Abstract Withdrawn
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M1.00304: High-speed AFM and the reduction of tip-sample forces Mervyn Miles, Ravi Sharma, Loren Picco High-speed DC-mode AFM has been shown to be routinely capable of imaging at video rate, and, if required, at over 1000 frames per second. At sufficiently high tip-sample velocities in ambient conditions, the tip lifts off the sample surface in a superlubricity process which reduces the level of shear forces imposed on the sample by the tip and therefore reduces the potential damage and distortion of the sample being imaged. High-frequency mechanical oscillations, both lateral and vertical, have been reported to reduced the tip-sample frictional forces. We have investigated the effect of combining linear high-speed scanning with these small amplitude high-frequency oscillations with the aim of reducing further the force interaction in high-speed imaging. Examples of this new version of high-speed AFM imaging will be presented for biological samples. [Preview Abstract] |
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M1.00305: Solving the focal shift problem in spatiotemporal focusing nonlinear microsocpy Kai Lou, Francois Amblard, Bo Wang, Steve Granick Fluorescence imaging deep into mouse lung and snail demonstrates a doughty nonlinear microscopy with wide field of view, high contrast, fast acquisition-rate and near diffraction-limited axial resolution based on an ordinary ultrafast oscillator and spatiotemporal focusing nonlinear microscopy design. The key idea is that focal shift matching promotes near-diffraction-limited axial fluorescence optical sectioning for both low and high NA objectives without laser extra-cavity alteration. [Preview Abstract] |
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M1.00306: Temperature and Magnetic Field Effects on the Raman Spectra of TaSe$_{\mathrm{2}}$ Jacob Harding, J.R. SImpson, A.R. Hight Walker In bulk form, TaSe$_{\mathrm{2}}$ exhibits transitions between commensurate and incommensurate charge-density wave (CDW) phases, and is attracting interest for advance device applications. In order to explore the evolution of the groundstate CDW phase, mechanical exfoliation of bulk crystals provides freshly cleaved surfaces and may be used to prepare few- to single-layer flakes. In the present work, we extended our opto-thermal Raman measurements [1] on MoS$_{\mathrm{2}}$ to include other TMDs, specifically TaSe$_{\mathrm{2}}$, in both \textit{1T} and \textit{2H} crystallographic phases. A novel, magneto-Raman microscope system affords measurement of low-frequency (down to 10cm$^{\mathrm{-1}})$ vibrational modes as a function of both temperature (\textasciitilde 10K to 300K) and magnetic field (0T to 9T). The dependence of the observed Raman-active phonons on temperature and magnetic field will be discussed and compared with earlier results on MoS$_{\mathrm{2}}$. Specifically, we observe the appearance of low-frequency, zone-folded modes in the CDW state, which soften with temperature similar to the higher frequency, in-plane $E_{2g}$ mode. Additionally, magnetic-field dependence, including Faraday rotation in the micro-crystal insert will be discussed. [1] R. Yan, J. R. Simpson, et al., ACS Nano 8, 986 (2014). [Preview Abstract] |
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M1.00307: The measurement of the Meissner effect of small superconductors by using of nano-SQUIDs Long Wu, Lei Chen, Xiaoyu Liu, Hao Wang, Xiaolei Wu, Zhen Wang The nano-SQUID (Superconducting QUantum Intereference Device) is considered one of the most sensitive magnetic sensors for the characterization of mesoscopic or microscopic magnetic property. Therefore, it can be used to measure the Meissner effect of small superconductors that cannot be measured by the commercial MPMS (Magnetic Property Measurement System). Here we demonstrate the measurement of the Meissner effect of a single indium particle (of 47 $\mu $m in diameter) and niobium particle (of 25 $\mu $m in diameter) by using of a nano-SQUID. By ramping the magnetic field slowly, we were able to observe a sharp Meissner effect transition of the small supercoductors which were greatly broadened in the commercial MPMS. In addition, the magnetic flux noise of our nanoSQUID measurement system is characterized and discussed. [Preview Abstract] |
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M1.00308: Open Loop Structure Low Cost Integrated Differential Inductive Micro Magnetic Volumetric Bio-Sensors Mohammad Khodadadi, Long Chang, Dimitri Litvinov This investigation proposes a study, model, simulate and experiment innovative very low cost Magnetic induction biosensor for point of care diagnostics. The biosensor consists of 2 ``semi-loops'' in a micro fluidic channel, one as a sensor and one as a reference, the design takes advantage of microfabrication processes to produce more precise structures to improve sensitivity. Besides the attractively low cost, this biosensor has many advantages. Since the detector is basically a shaped wire, it is inherently robust and reliable. Typical errors in fabricating the wires will not affect its performance and it is sensing volumetric, unlike GMR-based sensors used in biosensor systems that boast single particle detection. Due to small dimensions the sensors do not need to be calibrated. This sensor also has a large range of detection since its sensitivity is proportional to the excitation frequency. Being able to sense Magnetic nano particles in the volume is an advantage in term of trapping MNPs and sensitivity and functionality. Basically, this new brilliant design, fill the gap between the fabricated sensors and hand wounded sensors. [Preview Abstract] |
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M1.00309: Quantifying the Effectiveness of Muon Detector Purification Systems Naomi Mburu, Roberto Guida, Beatrice Mandelli The experiments along the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) were developed to study the fundamental particles that govern our universe. These experiments utilize gaseous detectors to track muons in the outermost portion of the experiment. For example, in the Compact Muon Solenoid (CMS) experiment three types of gaseous detectors are used as muon trackers: Resistive Plate Chambers (RPCs), Drift Tubes (DTs) and Cathode Strip Chambers (CSCs). RPCs use a gas mixture of Freon (C$_{2}$H$_{2}$F$_{4})$, sulfur hexafluoride (SF$_{6})$ and isobutane (iC$_{4}$H$_{10})$. The components of this gas mixture are both expensive and have high global warming potentials, so most of the gas mixture must be recycled and purified through a gas recirculation system. For this reason, RPCs employ purification systems that remove impurities due to the contamination and irradiation of the gas mixture that occur during normal operation of the LHC. Ion selective electrodes, gas chromatography, and mass spectrometry are set up and employed to study impurities produced in the RPCs and to quantify the ability of the purification systems to remove these impurities. [Preview Abstract] |
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M1.00310: Development and application of protein kinase A biosensor for cancer diagnosis. Chiun-Jye Yuan, Jhao-Hong Lee Cancer remains the leading cause of death worldwide in recent years. The protein kinase A (PKA) was proposed to be a cancer biomarker, because its catalytic subunit was demonstrated to be released as an extracellular protein kinase A (ECPKA) in medium of many cancer cell lines and in the serum of malignant cancer patients. In this study an electrochemical PKA biosensing platform was developed by the impedance spectroscopy (EIS)-based technology for the detection of ECPKA activity. The novel multiplex printed gold electrodes were also design and developed in this study for the multiplex detection and calibration during the measurements. The developed PKA biosensor exhibit high sensitivity to PKA activity with a linear range of detection from 0.01 U/mL to 50 U/mL and a lowest detection limit of 0.005 U/mL. The IC50 for the specific PKA inhibitor, H89, determined on the developed PKA biosensor is comparable to that determined by conventional methods. In conclusion, a quick, sensitive, reliable and cost-effective cancer diagnostic system for quick clinical cancer diagnosis is developed in this study. [Preview Abstract] |
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M1.00311: Characterization of the Optical Signal of Nanostructures by Surface Enhanced Raman Spectroscopy Nickalas Reamer, Michael Reardon, Arlene Ford Metal nanostructures exhibit interesting optical properties because of the ability of their free electrons to oscillate and form surface plasmons. These free electrons can be made to oscillate by utilizing a light source at an angle incident to the metal surface. The metal nanostructure will absorb the light incident to its surface causing the electrons to oscillate or resonate. This is called surface plasmon resonance (SPR). In this work, we report on the construction and operation of an optical system that will use transmission and reflection surface enhanced raman spectroscopy to analyze arrays of plasmonic nanohole structures. We will also show how surface enhanced raman spectroscopy signals can be used to analyze nanoparticles of varying sizes. [Preview Abstract] |
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M1.00312: Development and Characterization of Dynamic Light Scattering Instrumentation to Determine Nanoparticle Size Sam Harding, Jacob Harding, Kate Holman, TJ Sebastian, Jeff Simpson Dynamic Light Scattering (DLS) provides a high-throughput and accurate measurement of particle sizes for monodisperse (MD), spherical nanoparticles (NPs). We report on the development and characterization of homebuilt DLS instrumentation to measure the size of MD NPs of gold and polystyrene. HeNe and Ar-ion lasers comprise the excitation sources for the scattering experiment. An avalanche photodiode detects the scattered light and an autocorrelation card analyzes the signal to provide a measurement of the translational diffusion coefficient, which allows for the determination of NP diameter. We have tested our apparatus using commercially-produced gold NPs in the range of 10nm to 200nm. Given the strong temperature-dependence of the viscosity, periodic ambient temperature measurements were used to produce dynamic values for viscosity and hence minimize uncertainty in the determination of NP size. Additionally, we will compare our DLS results to NP size measurements obtained by Atomic Force Microscopy (AFM). S.H., K.H., T.J.S. and J.H. acknowledge support from Towson University. J.R.S. acknowledges support from NSF - CBET {\#}1236083. [Preview Abstract] |
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M1.00313: Digital holographic microscopy Solomon Barkley, Thomas Dimiduk, Vinothan Manoharan Digital holographic microscopy is a 3D optical imaging technique with high temporal ($\approx~$ms) and spatial ($\approx 10$~nm) precision. However, its adoption as a characterization technique has been limited due to the inherent difficulty of recovering 3D data from the holograms. Successful analysis has traditionally required substantial knowledge about the sample being imaged (for example, the approximate positions of particles in the field of view), as well as expertise in scattering theory. To overcome the obstacles to widespread adoption of holographic microscopy, we developed HoloPy -- an open source python package for analysis of holograms and scattering data. HoloPy uses Bayesian statistical methods to determine the geometry and properties of discrete scatterers from raw holograms. We demonstrate the use of HoloPy to measure the dynamics of colloidal particles at interfaces, to ascertain the structures of self-assembled colloidal particles, and to track freely swimming bacteria. The HoloPy codebase is thoroughly tested and well-documented to facilitate use by the broader experimental community. [Preview Abstract] |
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M1.00314: An Automated, High-Throughput System for GISAXS and GIWAXS Measurements of Thin Films Eric Schaible, Jessica Jimenez, Matthew Church, eunhee Lim, Polite Stewart, Alexander Hexemer Grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS) are important techniques for characterizing thin films. In order to meet rapidly increasing demand, the SAXSWAXS beamline at the Advanced Light Source (beamline 7.3.3) has implemented a fully automated, high-throughput system to conduct SAXS, GISAXS and GIWAXS measurements. An automated robot arm transfers samples from a holding tray to a measurement stage. Intelligent software aligns each sample in turn, and measures each according to user-defined specifications. Users mail in trays of samples on individually barcoded pucks, and can download and view their data remotely. Data will be pipelined to the NERSC supercomputing facility, and will be available to users via a web portal that facilitates highly parallelized analysis. [Preview Abstract] |
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M1.00315: Image Reconstruction for Low Dose Scanning Electron Microscopy. Petru Fodor, Alina Lazar Scanning electron microscopy is one of the most popular characterization techniques in material science, natural sciences, and nanotechnology when high resolution surface characterization is required. However, due to complex noise profiles associated both with the electron signal production, as well as the signal processing units the signal-to-noise ratio for data collection can be quite low. The typical way to address this issue is to increase the dwell time that the electron beam spends at each point during the acquisition process, and thus average out the random fluctuations in the signal. However, this is not possible for many organic samples and some inorganic ones such as zeolites which are highly susceptible to the thermal damage associated with long exposures to the imaging electron beam. In this work we describe methodologies based on block-matching to reconstruct accurate results from noisy images acquired at low doses/fast speeds. To this end we develop a model for the typical noise profiles encountered in electron microscopy. The strategies proposed are transferable to other imaging methods used in material science, such as composition mapping. [Preview Abstract] |
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M1.00316: Design and fabrication of two probes for Near Field THz imaging . Angelica Garcia, Gaudencio Paz, Joel Perez, Naser Qureshi THz imaging has gained attention due to the potential applications in medicine, security, inspections on semiconductor devices, etc. Until now, systems devoted to Near Field THz imaging consist of two basic parts: generation of THz radiation and a sensing probe system. In this work we present two approaches to make a probe for near field THz imaging. The first one is a novel device capable of integrate in a single chip the THz source with the sensing system. The device is fabricated in a GaAs substrate, on one side a photoconductive gold antenna is printed using microfabrication techniques; on the opposite side a specifically designed bow tie sub-wavelength sized bow-tie aperture is placed centered to the gap of the antenna. According to our simulations, the aperture exhibits field enhancement at the metal tips when it is illuminated from the substrate side by the THz radiation emitted from the antenna. The second device is a tapered conical waveguide with micrometrical aperture size at the end. A commercial silicon lens is used to focus the THz radiation emitted from a photoconductive antenna on the aperture. Simulation in COMSOL is used to find the best taper angle where reflection and loss are reduced. [Preview Abstract] |
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M1.00317: Application of a digital data acquisition system for time of flight Positron annihilation-induced Auger Electron Spectroscopy R W Gladen, V A Chirayath, A D McDonald, A J Fairchild, M D Chrysler, S K Imam, A R Koymen, A H Weiss We describe herein a digital data acquisition system for a time-of-flight Positron annihilation-induced Auger Electron Spectrometer. This data acquisition system consists of a high-speed digitizer collecting signals induced by Auger electrons and annihilation gammas in a multi-channel plate electron detector and a BaF2 gamma detector, respectively. The time intervals between these two signals is used to determine the times of flight of the Auger electrons, which are analyzed by algorithms based on traditional nuclear electronics methods. Ultimately, this digital data acquisition system will be expanded to incorporate the first coincidence measurements of Auger electron and annihilation gamma energies. [Preview Abstract] |
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M1.00318: Ultrasound pulse-echo setup for studying elastic properties of materials Oleksiy Svitelski, Peter Crossman, Susan Brown, David Lee The ultrasound pulse-echo technique is an invaluable non-destructive tool for the scientific exploration of the elastic properties of materials. We recently proposed a new design for such an instrument based on commercially available, mass-produced microchips [1]. Our measurements on a sample ferroelectric crystal of KTaNbO$_{3}$ demonstrate the superior performance of the instrument, achieving phase sensitivity of $\sim$ 0.06 degrees and amplitude sensitivity of $\sim$ 0.05 dB with an input signal S/N ratio of 3. We have since continued to refine this instrument’s capabilities through additional RF shielding and structural damping, and by the addition of static-discharge protection circuitry on the input. With these modifications, we hope to facilitate elasticity measurements in the presence of strong electric fields. \newline 1. J. Grossmann, A. Suslov, G. Yong, L. Boatner, O. Svitelskiy, Rev. Sci. Instr., v. 87, 044901 (2016). [Preview Abstract] |
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M1.00319: Using a Photon Beam for Thermal Nociceptive Threshold Experiments Azida Walker, Jeffery Anderson, Spencer Sherwood In humans, risk of diabetes and diabetic complications increases with age and duration of prediabetic state. In an effort to understand the progression of this disease scientists have evaluated the deterioration of the nervous system. One of the current methods used in the evaluation of the deterioration of the nervous system is through thermal threshold experiments. An incremental Hot / Cold Plate Analgesia Meter (IITC Life Science,CA is used to linearly increase the plate temperature at a rate of 10 \textordmasculine C min-1 with a cutoff temperature of 55 \textordmasculine C. Hind limb heat pain threshold (HPT) will be defined as a plate temperature at which the animal abruptly withdraws either one of its hind feet from the plate surface in a sharp move, typically followed by licking of the lifted paw. One of the disadvantages of using this hot plate method is in determining the true temperature at which the paw was withdrawn. While the temperature of the plate is known the position of the paw on the surface may vary; occasionally being cupped resulting in a temperature differentiation between the plate and the paw. During experiments the rats may urine onto the plate changing the temperature of the surface again resulting in reduced accuracy as to the withdrawal threshold. We propose here a new method for nociceptive somatic experiments involving the heat pain threshold experiments. This design employs the use of a photon beam to detect thermal response from an animal model. The details of this design is presented. [Preview Abstract] |
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M1.00320: Design, Construction, and Testing of MOKE Magnetometer Tighe Bailey, Casey W. Miller We report on the construction of a transverse magneto-optical Kerr effect (MOKE) magnetometer using various optical and electrical components. Uniquely, our MOKE magnetometer is able to sweep the magnetic field at frequencies greater than one Hz using lock in amplifiers to simultaneously sample the photodetector and the Hall sensor. The buffer of a lock-in amplifier allows for 512 samples per second, which allow us to rapidly sweep the magnetic field without loss of resolution. This drastically cuts down on the time taken per scan. To demonstrate the MOKE’s capabilities, scans were performed on multiple thin film magnetic structures, both with and without significant magnetic anisotropy. We were able to measure room temperature hysteresis loops of ferromagnets, such as Ni$_{80}$Fe$_{20}$. Our sample rotation capabilities allowed us to study the angular dependence of the exchange and magnetocrystalline anisotropy in bilayer structures. [Preview Abstract] |
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M1.00321: Neutron Scattering "Halo'' Observed in Highly Oriented Pyrolytic Graphite Lilin He, William Hamilton, Tao Hong, Lowell Crow, Bailey Katherine, Nidia Gallego We report the first observation of a ``Halo'' ring in the small-angle neutron scattering (SANS) region of highly oriented pyrolytic graphite (HOPG). The scattering presents as a ring with a half cone angle \textasciitilde 12.3$^{\circ}$ , which is nearly independent of the incident wavelength and persists to wavelengths far beyond the Bragg cutoff for graphite (6.71{\AA}). At normal incidence to the honeycomb lattice planes of HOPG the ring is centered about their normal. When the sample is tilted the ring moves in the same direction as the normal. However the shift or the scattering ring is less than the sample tilt and varies with wavelength. The ring broadens and splits into doublets with increasing wavelength. As the ring cone shifts it narrows down on the side of the cone's moving direction while it broadens in the opposite side. Additionally, the ring broadens and weakens with decreasing HOPG quality. We also notice that the peak intensity linearly scales with the sample thickness. Inelastic neutron scattering measurements show the neutrons in the ring have gained a couple of meV. We infer that this ``Halo'' effect might be induced by the sinusoidally curved surface of crystallites, coupled with low energy phonon scattering. This finding may open a new avenue to guide neutrons by modifying the surface shape of materials. [Preview Abstract] |
(Author Not Attending)
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M1.00322: A measurement platform for studying wetting phenomena at the nanoscale Michael Engel, Peter Bryant, Ronaldo Giro, Rodrigo Neumann, Phaedon Avouris, Mathias Steiner Understanding surface wetting and liquid-solid interactions at small scales is an important scientific task with broad technological implications. We report on the design, development, and application of an integrated analysis platform to experimentally characterize liquids at the nanoscale. The platform provides an integrated, graphene-based electronic sensor array for \textit{in-situ }optical micro-spectroscopy and atomic force microscopy. We demonstrate the experimental capabilities of the platform by applying various measurement functionalities. Specific demonstrations include electrical differentiation between liquids supported by Raman spectroscopic characterization, as well as monitoring surface wetting dynamics in real time. Finally, we explore the sensitivity limits of the platform by recording topographies and optical spectra of individual oil droplets with volumes of less than ten attoliters. Due to its integrated nanoscale measurement capabilities, the platform will have useful applications in scientific research and technology development. [Preview Abstract] |
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M1.00323: Simultaneous multiple samples investigation with digital holographic microscopy Nava Subedi, Matthew Berg This work explores several techniques in digital holography to image 10-300 microns sized particles and provide information useful for their characterization. In particular, digital holograms are formed with both forward- and backward-scattered light from samples fixed to a glass stage. Images of these particles are then rendered from the holograms that reveal aspects of the particle-surface structure. The forward- and backward-scattered light holograms are obtained simultaneously so that a side-by-side comparison of the two images is possible. In addition, this work also explores the simultaneous multiple samples investigation technique with digital holographic microscopy. This work could be supportive to insight more on the particles' morphology and subsequently improve the microparticles characterization technique for broad range applications. [Preview Abstract] |
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M1.00324: MATTER AT EXTREME CONDITIONS |
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M1.00325: Mechanical response of ultralight nickel kagom\'{e} structure to compression Pankaj Rajak, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta Deformation behavior of an ultralight architecture consisting of hollow Ni nanotubes and solid nanorods arranged as a 3-D kagom\'{e} structure is studied using Molecular dynamics simulations. As a precursor, we have also investigated mechanical response of a single hollow Ni nanotube and nanorod under uniaxial compression. We observe that 1/6(112) Shockley partial dislocations and twin formation at 3.5{\%} compression collapse the nanotube and nanorod. Kagom\'{e} structure made from solid nanorods shows deformation both near the node of kagom\'{e} lattice and the eight beams connected to it for compression above 5{\%}. In the case of hollow nanotube architecture, most of the deformation is observed near the node of the kagom\'{e} structure for strains higher than 6{\%}. At 8{\%} and 12.5{\%} compression, we observe plastic buckling of solid and hollow architecture, respectively. Hence hollow nanotube architecture can withstand much larger compression with very little deformation of the system than the solid nanorod architecture. The deformation in all these systems is caused by 1/6(112) Shockley partial and 1/2(110) dislocations. [Preview Abstract] |
(Author Not Attending)
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M1.00326: Many-electron effects at extreme conditions. Igor Abrikosov Using theoretical simulations at the level of Dynamical Mean-Field Theory combined with DFT (DFT$+$DMFT) coupled to advanced experimental studies of materials at extreme conditions we show that many-electron effects have strong influence on the electronic structure and properties of transition metals, their alloys and compounds. In particular, correlation effects are essential for a description of the pressure induced insulator-to-metal transitions (IMT). We illustrate this by considering IMTs in transition metal oxides [1,2]. Moreover, considering hcp Fe and Os, we show that including correlation effects is necessary for the description of the topological changes of the Fermi surface for valence electrons at high pressure, the so-called electronic topological transition (ETT) [3,4]. Considering Fe at the conditions of the Earth's core, we show that DFT$+$DMFT calculations allow one for better understanding of the Earth's geodynamo [5,6]. [1] V. Potapkin \textit{et al.}, Phys. Rev. B 93, 201110(R) (2016). [2] I. Leonov \textit{et al.}, Phys. Rev. B 94, 155135 (2016). [3] K. Glazyrin\textit{, et al.}, Phys. Rev. Lett. 110, 117206 (2013). [4] L. Dubrovinsky \textit{et al.}, Nature 525, 226--229 (2015). [5] L. V. Pourovskii \textit{et al.}, Phys. Rev. B 87, 115130 (2013). [6] L. V. Pourovskii \textit{et al.}, arXiv:1603.02287 [cond-mat.str-el]. [Preview Abstract] |
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M1.00327: Effect of vacancy formation in solid iron under high pressure Jin-Chun Li, Dong-Bo Zhang, Tao Sun Solid iron has been widely used in material engineering, and it is proposed as the fundamental component of the Earth's core, so magnetic and mechanical properties of iron at high pressure have~attracted extensively experimental and theoretical studies. In this work, we perform systematic calculations to investigate the lattice constants, enthalpy, magnetic moment, elastic properties of perfect crystalline solid iron for a wide range of pressures by using first-principles. Then, in order to study the effect of point defect in the solid iron in extreme conditions, the mono-vacancy is involved in stability, magnetic and elastic properties of iron. Furthermore, different sized supercells within mono-vacancy model are applied to research pressure influence on vacancy concentration. [Preview Abstract] |
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M1.00328: Advanced Spectral Analysis Program (ASAP) for High-Pressure X-ray Diffraction Jeffrey Montgomery A program for analyzing large powder diffraction data sets has been developed. This tool enables the user to fit any type of crystal structure by indexing peaks in multiple files simultaneously by manually selecting them from a 2D plot of peak positions. The program has tools for automatic peak fitting and pressure determination using various equations of state. The interface is useful for correlating information from various types of spectral data, and so tools have been added for analyzing common fluorescence markers such as ruby, strontium tetraborate, and diamond. The program operation is demonstrated by the analysis of high-pressure powder x-ray diffraction data taken on a sample of vanadium metal at the Advanced Photon Source 16-BMD beamline. Samples were compressed in three runs to a pressure of 70 GPa in an attempt to measure the phase transition from bcc to orthorhombic in hydrostatic and non-hydrostatic conditions. Using ASAP to analyze this data provides a fast and accurate tool for observation of such a subtle transition, which is characterized primarily by a narrow splitting of the bcc 110 and 112 peaks. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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M1.00329: Topological investigation of nuclear graphite using small angle scattering Durgesh K. Rai, Boris Khaykovich, Anne A. Campbell, Jan Ilvasky, Yutai Katoh, Lance L. Snead Nuclear power reactors require high performance materials that withstand high temperatures and neutron damage over long period of times. Graphite is widely used for high temperature fission reactor applications. It has a complex multiphase microstructure, which is affected by neutron irradiation. The irradiation-induced microstructures result in significant thermophysical property changes, affecting service lifetimes. It is important to understand these life-limiting phenomena at many different length scales. We present the results from small angle scattering (SAS) studies on graphite samples, which vary in doses and irradiation temperatures. The neutron and synchrotron SAS measurement data indicates that the graphite morphology consists of surface fractal structures. The samples were found to be uniform across several decades of length scale, while exhibiting different surface fractal dimensions, for different irradiation doses and temperature conditions. The surface fractal dimension changes at \textless 10nm length scale for the sample irradiated at a temperature of \textasciitilde 622 $^{\circ}$ C, but not for the sample irradiated at \textasciitilde 345 $^{\circ}$ C. [Preview Abstract] |
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M1.00330: Extreme State of Matter: Shock Experiments and Simulations Vladimir Fortov The behavior of matter at extremely high pressures is very interesting for understanding the structure and evolution of astrophysica objects and many modern energy technologies. Dynamic investigations of warm dense matter at extremely high pressures, based on shock loading, adiabatic release of shocked as well as quasi-isentropic compression are considered. To generate shock waves in the terapascal pressure range, the cylindrical and spherical condensed high explosives, laser and corpuscular beams, high velocity impacts, and soft X-rays were used. The high-resolved temporal diagnostics of the extreme states of plasma were carried out with VIZAR technique, fast acting electron-optical transducers, pyrometers, and high-speed spectrometers equipped with the electron-optical transmission lines. The experimental data obtained and the physical models of behavior of plasma at extremely high pressures, temperatures and strain rates are discussed. [Preview Abstract] |
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M1.00331: High-Strain-Rate Deformation Behavior of Polyolefins David Bucknall, Naresh Thadhani, Iain Condie, Amanda Luce Polymers are being increasingly used in dynamic or high-strain-rate loading environments for applications such as in automobile and aerospace vehicles, sports equipment and protective. However, despite the use of various experimental methods to study polymer deformation under these extreme conditions, their fundamental behavior is poorly understood. To understand the behaviour, we have undertaken a series of Taylor impact measurements on a series of polyolefins. By combining high-speed optical imaging, with time-resolved spectroscopic and thermal imaging, we have been able to determine the transient deformation behavior. In addition, we have supplemented these data with ex-situ electron spin resonance (ESR) and gel permeation chromatography (GPC) measurements to explain the observed high-strain-rate deformation behavior at impact velocities of up to 500 m/s in various polyolefins In this presentation we will highlight the key results of the impact tests and our understanding of the high-strain-rate deformation behavior of polyolefins. [Preview Abstract] |
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M1.00332: CHEMICAL PHYSICS |
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M1.00333: Search for O[-1] earthquake-like precursors: a ME$\mu $\textbf{SR MgO study } C Boekema, A Cabot, A-L Lee, I Lin, A Colebaugh, FT Freund We study O$^{\mathrm{-1}}$ earthquake-like precursor effects [1,2] by analyzing Muon-Spin-Resonance ($\mu $SR) MgO data using Maximum Entropy (ME). [3,4] Due to its presence in the Earth's crust, MgO is ideal to study these features. O$^{\mathrm{-1}}$ formation results from a 2-stage break-up in an O anion pair at high-temperature or high-pressure conditions. [2] As T increases above room temperature, a small {\%} of oxygen is predicted to produce an O$^{\mathrm{-1}}$ state. ME analysis of 100-Oe $\mu $SR data of a pure 3N-MgO single crystal produces a broad Gaussian at 1.36 MHz and a sharp Lorentzian at 1.4 MHz. The latter could be effects of extended O$^{\mathrm{-1}}$ states, as positive muons probe near O ions. There is no sharp 1.4-MHz signal observed in the $\mu $SR data of insulators Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ [5] and PrBCO$_{\mathrm{6}}$ data, only the expected 100-Oe Gaussian. We have fitted ME$\mu $SR transforms of MgO to obtain an empirical description of 1.36- and 1.4- MHz peaks. Their T dependences above room temperature appear to be positive-hole effects. Relations to precursor earthquake-like O-valency effects are discussed. Research supported by ISIS-UK, LANL--DOE, SETI-NASA, SJSU {\&} AFC. 1] FT Freund, Nat Hazards Earth Sys Sci \textbf{7} (2007) 1. 2] FT Freund \textit{et al,} Phys Chem Earth \textbf{31} (2006) 389. 3] C Boekema and MC Browne, MaxEnt 2008, AIP Conf Proc {\#}1073 p260. 4] S Lee \textit{et al,} HUIC Educ, Math {\&} Eng Tech Conf, Uo HI (2013); C Boekema \textit{et al}, Bull Am Phys Soc, March 2015. 5] C Boekema \textit{et al}, Hyperfine Interactions 32 (1986) 667. [Preview Abstract] |
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M1.00334: A simple model for electronic properties of surface adsorbed molecules. Rajesh Dhakal, William Schwalm We adapt a minimal approximation to one electron quantum theory of molecules referred to as Fast Accurate-Kinetic Energy method by F. Harris et al. to a Green function formalism. This in principle handles large complex molecular structures with less computational effort to compute electronic properties of adsorbed molecules. Kinetic energy integrals are calculated accurately but multi-electron potential energy integrals are approximated. The neighboring atom interactions are included also. The calculations are iterated to achieve a rough charge self-consistency. The method is expected to obtain qualitative suggestions of spectral features that can appear in experiments, thus relating such features conceptually to the physics of adsorbate systems. In the work presented, we study properties of graphene with adsorbate systems including isolated hydrogen atoms and vacancies in graphene lattice. [Preview Abstract] |
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M1.00335: Development of a Coarse-grained Model of Polypeptoids for Studying Self-assembly in Solution Pu Du, Steven Rick, Revati Kumar Polypeptoid, a class of highly tunable biomimetic analogues of peptides, are used as a prototypical model system to study self-assembly. The focus of this work is to glean insight into the effect of electrostatic and other non-covalent secondary interactions on the self-assembly of sequence-defined polypeptoids, with different charged and uncharged side groups, in solution that will complement experiments. Atomistic (AA) molecular dynamics simulation can provide a complete description of self-assembly of polypeptoid systems. However, the long simulation length and time scales needed for these processes require the development of a computationally cheaper alternative, namely coarse-grained (CG) models. A CG model for studying polypeptoid micellar interactions is being developed, parameterized on atomistic simulations, using a hybridized approach involving the OPLS-UA force filed and the Stillinger-Weber (SW) potential form. The development of the model as well as the results from the simulations on the self-assembly as function of polypeptoid chemical structure and sequences will be presented. [Preview Abstract] |
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M1.00336: Finite-size effects in simulations of electrolyte solutions under periodic boundary conditions Jeffrey Thompson, Isaac Sanchez The equilibrium properties of charged systems with periodic boundary conditions may exhibit pronounced system-size dependence due to the long range of the Coulomb force. As shown by others [S. Chiesa {\it et al.}, Phys. Rev. Lett. {\bf 97}, 076404 (2006)], the leading-order finite-size correction to the Coulomb energy of a charged fluid confined to a periodic box of volume~$V$ may be derived from sum rules satisfied by the charge--charge correlations in the thermodynamic limit~$V \to \infty$. In classical systems, the relevant sum rule is the Stillinger--Lovett second-moment (or perfect screening) condition. This constraint implies that for large~$V$, periodicity induces a negative bias of $-k_{\rm B} T (2V)^{-1}$ in the total Coulomb energy density of a homogeneous classical charged fluid of given density and temperature [J. P. Thompson and I. C. Sanchez, J. Chem. Phys., in press]. We present a careful study of the impact of such finite-size effects on the calculation of solute chemical potentials from explicit-solvent molecular simulations of aqueous electrolyte solutions. [Preview Abstract] |
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M1.00337: Systematic and Simulation-Free Coarse Graining of Polymers Qiang Wang Coarse-grained (CG) models are currently needed to study polymeric systems, as full atomistic simulations of many-chain systems used in experiments are in most cases not feasible due to their formidable computational requirements. Polymeric systems are also best suited for coarse graining, as the large number of monomers on each chain allows high levels of coarse graining. Here we introduce a systematic and simulation-free strategy for coarse graining polymeric systems, and apply it to the structure-based and relative-entropy-based coarse graining of homopolymers, polymer blends, and diblock copolymers in the melt state. We use the well-developed polymer reference interaction site model theory, instead of many-chain molecular simulations, for both the original and CG systems, and examine how the CG potentials vary with the coarse-graining level and how well the CG models at different levels can reproduce the structure and thermodynamic properties of the original system. Our strategy is quite general and versatile. It is at least several orders of magnitude faster than those using many-chain simulations, thus effectively solving the transferability problem in coarse graining. It also avoids the problems caused by finite-size effects and statistical uncertainties in many-chain simulations commonly used in coarse graining. [Preview Abstract] |
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M1.00338: Coarse-grained modeling of polycrystalline ice in supercooled water. Henry Chan, Mathew Cherukara, Badri Narayanan,, Chris Benmore, Stephen Gray, Sankaranarayanan Subramanian Formation and growth of grains of ice is ubiquitous, influencing naturally occurring phenomena such as glacier formation and processes happening at the nanoscale, like intracellular freezing. Despite the exponential growth in computing resources, it remains a grand challenge to simulate phase transitions and dynamical processes in deeply supercooled systems due to limitations imposed by system sizes and timescales which is further compounded by their sluggish kinetics. We will present our work on probing the formation and grain growth in polycrystalline ice using coarse-grained molecular dynamics on multi-million molecule systems for up to microsecond time scales. Our findings highlight the distinct differences between grain growth mechanisms of ice compared to those in metals and ceramics. [Preview Abstract] |
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M1.00339: Coarse gaining of molecular crystals: limitations imposed by molecular flexibility Catalin Picu, Anirban Pal Molecular crystals include molecular electronics, energetic materials, pharmaceuticals and some food components. In many of these applications the small scale mechanical behavior of the crystal is important such as for example in energetic materials where detonation is induced by the formation of hot spots which are induced thermomechanically, and in pharmaceuticals where phase stability is critical for the biochemical activity of the drug. Accurate modeling of these processes requires resolving the atomistic scale details of the material. However, the cost of these models is very large due to the complexity of the molecules forming the crystal, and some form of coarse graning is necessary. In this study we identify the limitations imposed by the need to accurately capture molecular flexibility on the development of coarse grained models for the energetic molecular crystal RDX. We define guidelines for the definition of coarse grained models that target elastic and plastic crystal scale properties such as elastic constants, thermal expansion, compressibility, the critical stress for the motion of dislocations (Peierls stress) and the stacking fault energy [Preview Abstract] |
(Author Not Attending)
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M1.00340: Derivation and application of transition state force fields for enantioselective catalysis Eric Hansen, Per-Ola Norrby, Olaf Wiest Standard methods of screening ligands for use in asymmetric, transition metal catalyzed reactions require experimentally screening hundreds of ligands, which is costly and requires specialized high-throughput machinery, and it is often a trial-and-error process. Accurate computational predictions of selectivity require extensive conformational sampling about the selectivity-determining transition state, but this process must be fast enough to compete with experimental screening techniques to be useful. Quantum to Molecular Mechanics can be used to computationally and rapidly predict the performance of ligands in asymmetric catalysis, while simultaneously providing an atomistic view of how they achieve their selectivity. The method has been applied successfully to a variety of transition metal catalyzed reactions that are both industrially and academically important. Herein, I will describe how we develop highly accurate molecular mechanics models of transition states from ab initio calculations and highlight several of their applications. [Preview Abstract] |
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M1.00341: `Exotic' Electron Spectroscopy of Molecules in Electric Fields Rajeev Pathak, Nalini Gurav, Shridhar Gejji Single molecules, whether polar or non-polar (in their free state), when subjected to an externally applied uniform electric field, are observed to exhibit remarkably different UV spectra from those of their zero-field counterparts. Significant spectral line-shifts, line-splitting, line-merging as well as disappearance, and emergence of `exotic' spectral lines are observed as a function of the applied electric field strength. In particular, we simulate the molecular electronic-transition spectra of methanol, hydrogen-peroxide, water and carbon-dioxide in an electric field, employing time dependent density functional theory (TD-DFT) under the versatile M06-2X dispersion-corrected DFT prescription. It is further demonstrated that the Natural Localized Molecular Orbitals (NLMOs), playing a dual donor-acceptor role, can best describe the electron density redistribution and the interplay of various bands in the UV spectrum which is traced back to mutations and crossings of the frontier molecular orbitals. [Preview Abstract] |
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M1.00342: Coherent two-dimensional spectroscopy of a Fano model Felipe Poulsen, Daniel Finkelstein-Shapiro, Tönu Pullerits, Thorsten Hansen The Fano line shape arises from the interference of two excitation pathways to reach a continuum. Its generality has resulted in a tremendous success in explaining the line shapes of many one-dimensional spectroscopies—absorption, emission, scattering, conductance, photofragmentation—applied to very varied systems—atoms, molecules, semiconductors, and metals. Unraveling a spectroscopy into a second dimension reveals the relationship between states in addition to decongesting the spectra. Femtosecond-resolved two- dimensional electronic spectroscopy (2DES) is a four-wave mixing technique that measures the time evolution of the populations and coherences of excited states. It has been applied extensively to the dynamics of photosynthetic units, and more recently to materials with extended band structures. In this paper, we solve the full time-dependent third-order response, measured in 2DES, of a Fano model and give the system parameters that become accessible. [Preview Abstract] |
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M1.00343: Magnetic Exchange Couplings from Local Spin Analysis Rajendra Joshi, Bayileyegn Akanie Abate, Juan Peralta We propose a method to calculate the magnetic exchange coupling parameters in transition metal complexes from a single spin-configuration. Our method uses constraint density functional theory and a local spin population analysis in combination to a non spin formalism to effectively extract the magnetic exchange parameter from the derivative of the electronic energy and spin pair correlation values. We show proof-of-concept calculations on the H-He-H systems and small transition metal complexes. [Preview Abstract] |
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M1.00344: First Principles Modeling and Interpretation of Ionization-Triggered Charge Migration in Molecules Adam Bruner, Sam Hernandez, Francois Mauger, Paul Abanador, Mette Gaarde, Ken Schafer, Ken Lopata Modeling attosecond coherent charge migration in molecules is important for understanding initial steps of photochemistry and light harvesting processes. Ionization triggered hole migration can be difficult to characterize and interpret as the dynamics can be convoluted with excited states. Here, we introduce a real-time time-dependent density functional theory (RT-TDDFT) approach for modeling such dynamics from first principles. To isolate the specific hole dynamics from excited states, Fourier transform analysis and orbital occupations are used to provide a spatial hole representation in the frequency domain. These techniques are applied to hole transfer across a thiophene dimer as well as core-hole triggered valence motion in nitrosobenzene. [Preview Abstract] |
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M1.00345: Nuclear Quantum Effects in H$^+$ and OH$^-$ Diffusion Along Confined Water Wires from Ab Initio Path Integral Molecular Dyanmics Mariana Rossi, Michele Ceriotti, David Manolopoulos Diffusion of H$^+$ and OH$^-$ along water wires provides an efficient mechanism for charge transport that is exploited by biological systems and shows promise in technological applications. However, what is lacking for a better control and design of these systems is a thorough theoretical understanding of the diffusion process at the atomic scale. Here we consider H$^+$ and OH$^-$ in finite water wires using density functional theory. We employ machine learning techniques to identify the charged species, thus obtaining an agnostic definition of the charge. We employ thermostated ring polymer molecular dynamics [1] and extract a ``universal'' diffusion coefficient from simulations with different wire sizes by considering Langevin dynamics on the potential of mean force of the charged species. In the classical case, diffusion coefficients depend significantly on the potential energy surface, in particular on how dispersion forces modulate O--O distances. NQEs, however, make the diffusion less sensitive to the underlying potential and geometry of the wire, presumably making them more robust to environment fluctuations [2]. [1] Rossi, Ceriotti, Manolopoulos, {\it JCP} {\bf 140}, 234116 (2014); [2] Rossi, Ceriotti, Manolopoulos, {\it JPCL} {\bf 7}, 3001 (2016). [Preview Abstract] |
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M1.00346: The Generalized Onsager Model and DSMC Simulations of High-Speed Rotating Flow with Swirling Feed Dr. Sahadev Pradhan The generalized Onsager model for the radial boundary layer and of the generalized Carrier-Maslen model for the axial boundary layer at the end-caps in a high-speed rotating cylinder ((S. Pradhan {\&} V. Kumaran, J. Fluid Mech., 2011, vol. 686, pp. 109-159); (V. Kumaran {\&} S. Pradhan, J. Fluid Mech., 2014, vol. 753, pp. 307-359)), are extended to incorporate the angular momentum of the feed gas for a swirling feed for single component gas and binary gas mixture. For a single component gas, the analytical solutions are obtained for the sixth-order generalized Onsager equations for the master potential, and for the fourth-order generalized Carrier-Maslen equation for the velocity potential. In both cases, the equations are linearized in the perturbation to the base flow, which is a solid-body rotation. The equations are restricted to the limit of high Reynolds number and (length/radius) ratio, but there is no limitation on the stratification parameter. The linear operators in the generalized Onsager and generalized Carrier-Maslen equations with swirling feed are still self-adjoint, and so the eigenfunctions form a complete orthogonal basis set. The analytical solutions are compared with direct simulation Monte Carlo (DSMC) simulations. The comparison reveals that the boundary conditions in the simulations and analysis have to be matched with care. When these precautions are taken, there is excellent agreement between analysis and simulations, to within 15{\%}. [Preview Abstract] |
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M1.00347: Cooperative FRET: Comparison between Interacting and Independent FRET Pathways in a Light Harvesting Network Paul Cunningham, Christopher Spillmann, Susan Buckhout-White, Joseph Melinger, Mario Ancona, Ellen Goldman, Igor Medintz Light harvesting antennae use F\"{o}rster Resonance Energy Transfer (FRET) between dyes to funnel energy to a reaction center. Inhomogenities in dipole orientation in distributions of static dyes reduce FRET efficiencies, via the large multiplicity of unfavorable orientations. Multiple FRET pathways may compensate for inhomogeneities. We examine multi-step FRET in a series of dye-labeled DNA rail scaffolds where the degree of interaction between two parallel rails was adjusted via their separation. We find that interacting pathways outperform simply redundant independent pathways. For one FRET step, addition of a second donor yields an unexpected increase in FRET efficiency. Monte-Carlo simulations show that suppression of inefficient FRET pathways causes this increase. As the number of donors increases, the FRET efficiency of a static distribution approaches the dynamic limit, where dyes are free to reorient. This suppression is optimal when the rails are close enough to allow fast homo-FRET between them. However, at close separations H-like aggregate formation can lead to energy sinks. These are important considerations when designing light harvesting networks and may aid in the understanding of incoherent hopping transport in other systems. [Preview Abstract] |
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M1.00348: Characterization of Fast Energy Transport Mechanisms in PEG Oligomers Layla Qasim, Arkady Kurnosov, Yuankai Yue, Alexander Burin, Igor Rubtsov Vibrational energy transfer in molecules can be ballistic, which is fast and efficient, or diffusive which is governed by random-walk IVR steps. Different regimes of intramolecular vibrational energy transport were studied in a series of terminally-functionalized PEG oligomers of various length by relaxation-assisted two-dimensional infrared spectroscopy. Energy transport was initiated through short mid-IR excitation on the localized end groups and the speed of vibrational transport in PEGs was measured to be 5.5 {\AA}/ps. The total through-chain transport time was detected up to 9.8 ps through 12 PEG units. To gain insight into the mechanism of energy transport, the dispersion relations of the PEG chain bands were calculated and indicated that although many bands are participate in energy transport, most of them do not have sufficient lifetimes to support ballistic transport for PEG oligomers exceeding 8 units. Theoretical modeling was performed and indicated that the transport is initially ballistic and then switches to a directed diffusive regime without abrupt changes of the transport speed. The approaches developed in this study are applicable to other chain types, particularly those involving heteroatoms in the backbone. [Preview Abstract] |
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M1.00349: Molecular exciton formation and energy transfer in a network of closely spaced dyes on a DNA scaffold Paul Cunningham, Susan Buckhout-White, Ellen Goldman, Igor Medintz, Joseph Melinger Natural light harvesting systems exploit both strong and weak electronic coupling between chromophores to efficiently funnel energy to a reaction center. Here we use the DNA duplex as a scaffold to organize dyes with 4 {\AA} precision and examine how tuning inter-dye electronic coupling from weakly to strongly coupled regimes effects resonance energy transfer (RET). We characterize an energy cascade of cyanine dyes rigidly linked to DNA with double attachment chemistry using ultrafast spectroscopy. When all inter-dye spacings are within 10 {\AA}, molecular excitons form that possess character from all dyes, and the excited state dynamics show only weak wavelength dependence, consistent with strong electronic coupling. Reducing the spectral overlap by varying the dyes in the cascade reduces the electronic coupling strength and restores RET-like interactions where energy sequentially moves down the cascade. Placing a terminal acceptor at a remote distance from the coupled dyes shows efficient energy transfer from the molecular exciton. This study may provide insight into methods of enhancing the energy transfer efficiencies in synthetic light harvesting networks by incorporating both strong and weak electronic couplings. [Preview Abstract] |
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M1.00350: Photoelectron Spectroscopy as a Probe of Molecular Clusters Relevant to Singlet Fission Steven Kregel, Glen Thurston, Etienne Garand The singlet fission (SF) process has recently become of great interest to the physical chemistry community due to its potential application to next-generation solar cells. The relative energetics of the singlet and triplet states involved in this process are of fundamental importance to SF, as is the magnitude of the inter-chromophore coupling. Due to this coupling, the electronic structure of small chromophore clusters is different from the bulk, as well as from isolated molecules. In order to study these systems we have constructed a new instrument consisting of a time of flight mass spectrometer coupled to a high resolution photoelectron spectrometer. Utilizing this instrument, we are able to generate small chromophore clusters (n$=$1-5) of known mass, and interrogate them individually with sensitivity to both singlet and triplet excited states. By utilizing anion photoelectron spectroscopy we can map out the energy landscape of the final neutral systems as a function of cluster size, while simultaneously directly measuring the magnitude of electronic coupling between individual chromophores. Preliminary studies with this instrument have focused on anthracene and tetracene which have been shown to exhibit SF in crystals, along with similar polyaromatic hydrocarbons. [Preview Abstract] |
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M1.00351: Observing Real-Time Electron-Hole Plasma Recombination to Lattice Heat Ming-Fu Lin, Max Verkamp, Kristin Benke, Kaili Zhang, Elizabeth Ryland, Clemens Weninger, Xiaozhe Shen, Renkai Li, Xijie Wang, David Fritz, Uwe Bergmann, Josh Vura-Weis Using tabletop extreme ultraviolet (XUV) transient absorption spectroscopy allows us to directly capture optical generated electron hole plasma and to monitor subsequent relaxation to lattice heat in real time. Lead iodide is optically excited at 3.1 eV and relaxation of generated electron hole pairs are measured by delayed XUV pulses which separately probe the partial density of states of iodine in valence and conduction bands, respectively. Short-lived core-level absorption features associated with transitions from iodine inner-shell 4$d$ electrons to valence and conduction bands are separated at optical excitation energy, corresponding to photo-generated electron and hole pairs that recombine and generate lattice heat in 5.6$\pm$ 0.6 ps. Ultrafast electron diffraction verifies the appearance of lattice vibration in several picoseconds in consistent with the XUV results. The obtained Debye-Waller response from electron diffraction further supports a full conversion of 3.1 eV photon energy to thermal heat in the lattice. Direct observation of electron-hole plasma using femtosecond XUV light source illustrates its ability to probe carrier recombination in real time with 50 fs and chemical element sensitivity. [Preview Abstract] |
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M1.00352: Femtosecond Polarization Phase Selective (PPS) High Magnetic Field Studies of Electron-Spin-Hole (ESH) Dynamics: New Tools for Ultrafast Imaging Fe-centered ESH Transfer Mechanisms Steps Kresimir Rupnik, Benjamin Cooper, Taylor Dunne, Katherine Gerosa, Kaitlyn Mercer, Stephen McGill In previous work, new Nanoparticle-enzyme Based Hybrids (NEBH) synthesis methods were investigated for nanoparticles of different shapes and electron energies. These hybrids can provide electromagnetic-field-driven ESH separations and transfers to desired molecular locations. Of paramount biomedical interest are the activity centers (including Fe-clusters) in proteins that perform their intended function and help synthesize other molecules. In this work we discuss results of our recent \textit{in situ} ESH dynamics measurements: we use \textless 15fs (Vitara) PPS broad band pulses and ultrahigh, 25T, magnetic fields from Split-helix magnet at NHMFL. Work included multi-spectral domain PPS harmonic generations and PPS sum frequency generations. Model compounds, including cytochromes, were used for testing and calibrations and previously studied Fe-S enzymes were prepared for measurements. While PPS opto-magnetic methods are known for their insight into electronic structure, our femtosecond measurements can provide ultrafast dynamic imaging of ESH mechanisms decision making steps. [Preview Abstract] |
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M1.00353: Structural phase transitions and time-resolved dynamics of solid-supported interfacial methanol observed by reflection electron diffraction Ding-Shyue Yang, Xing He, Chengyi Wu Due to their large scattering cross sections with matter, electrons are suitable for contactless probing of solid-supported surface assemblies, especially in a reflection geometry. Direct visualization of assembly structures through electron diffraction further enables studies of ultrafast structural dynamics through the pump-probe scheme as well as discoveries of hidden phase changes in equilibrium that have been obscure in spectroscopic measurements. In this presentation, we report our first observation of unique two-stage transformations of interfacial methanol on smooth hydrophobic surfaces. The finding may reconcile the inconsistent previous reports of the crystallization temperature using various indirect methods. Dynamically, energy transfer across a solid-molecule interface following photoexcitation of the substrate is found to be highly dependent on the structure of interfacial methanol. If it is only 2-dimensionally ordered, as the film thickness increases, a prolonged time in the decrease of diffraction intensity is seen, signifying an inefficient vibrational coupling in the surface normal direction. Implications of the dynamics results and an outlook of interfacial studies using time-resolved and averaged electron diffraction will be discussed. [Preview Abstract] |
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M1.00354: The isotropic local Wigner-Seitz model: An accurate theoretical model for the quasi-free electron energy in fluids Cherice Evans, Gary L. Findley The quasi-free electron energy $V_0(\rho)$ is important in understanding electron transport through a fluid, as well as for modeling electron attachment reactions in fluids. Our group has developed an isotropic local Wigner-Seitz model that allows one to successfully calculate the quasi-free electron energy for a variety of atomic and molecular fluids from low density to the density of the triple point liquid with only a single adjustable parameter. This model, when coupled with the quasi-free electron energy data and the thermodynamic data for the fluids, also can yield optimized intermolecular potential parameters and the zero kinetic energy electron scattering length. In this poster, we give a review of the isotropic local Wigner-Seitz model in comparison to previous theoretical models for the quasi-free electron energy. \emph{Acknowledgments: All measurements were performed at the University of Wisconsin Synchrotron Radiation Center. This work was supported by a grants from the National Science Foundation (NSF CHE-0956719), the Petroleum Research Fund (45728-B6 and 5-24880), the Louisiana Board of Regents Support Fund (LEQSF(2006-09)-RD-A33), and the Professional Staff Congress – City University of New York.} [Preview Abstract] |
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M1.00355: The Effect of Water Molecules on Mechanical Properties of Cell Walls Nima Rahbar, Sina Youssefian The unique properties of bamboo fibers come from their natural composite structures that comprise mainly cellulose nanofibrils in a matrix of intertwined hemicellulose and lignin called lignin-carbohydrate complex (LCC). Here, we have utilized atomistic simulations to investigate the mechanical properties and mechanisms of interactions between these materials, in the presence of water molecules. The role of hemicellulose found to be enhancing the mechanical properties and lignin found to be providing the strength of bamboo fibers. The abundance of Hbonds in hemicellulose chains is responsible for improving the mechanical behavior of LCC. The strong van der Waals forces between lignin molecules and cellulose nanofibrils are responsible for higher adhesion energy between LCC/cellulose nanofibrils. We also found out that the amorphous regions of cellulose nanofibrils is the weakest interface in bamboo Microfibrils. In presence of water, the elastic modulus of lignin increases at low water content and decreases in higher water content, whereas the hemicellulose elastic modulus constantly decreases. The variations of Radial Distribution Function and Free Fractional Volume of these materials with water suggest that water molecules enhance the mechanical properties of lignin by filling voids in the system and creating Hbond bridges between polymer chains. For hemicellulose, however, the effect is always regressive due to the destructive effect of water molecules on the Hbond of its dense structure. [Preview Abstract] |
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M1.00356: Thermodynamics of Hydration of Fullerols [C$_{\mathrm{60}}$(OH)$_{\mathrm{n}}$] and Hydrogen -- Bond Dynamics in the Hydration Shells Sonanki Keshri, Bhalachandra Tembe Molecular dynamics simulations of fullerene and the water soluble derivatives of fullerene i.e. fullerols [C$_{\mathrm{60}}$(OH)$_{\mathrm{n}}$, where n $=$ 2 to 30] in aqueous solutions have been performed for the purpose of obtaining a detailed understanding of the structural and dynamic properties of these nanoparticles in water. The study is motivated by the diverse biological applications of water-soluble fullerols. From the analysis of radial distribution functions, we have found that water molecules form two solvation shells around the central solute molecule. Hydrogen bonding in the bulk solvent is unaffected by increasing n. There is a large increase in H-bonding between solute and solvent molecules as we increase n. The diffusion constants of solute molecules decrease with increasing n. The fullerene molecules are found to have a very high $\Delta $G in water ($\Delta $G $=$ 52.8 kJ/mol), whereas a very low $\Delta $G of C$_{\mathrm{60}}$(OH)$_{\mathrm{30\thinspace }}$ ($\Delta $G $=$ -427.1 kJ/mol) in water have been found. Our simulation results reveal that the hydrophobic character of fullerene is reduced with surface hydroxylation. [Preview Abstract] |
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M1.00357: Synthesis and Reactive Characterization of Aluminum Iodate Hexahydrate Crystals Dylan Smith, Michelle Pantoya A monomolecular aluminum based explosive crystal has been synthesized from aluminum particles dissolved in iodic acid solution. The precipitate from solution is aluminum iodate hexahydrate (Al(IO$_{3})_{3}$(HIO$_{3})_{2}$(H$_{2}$O)$_{6})$, as confirmed by X-ray diffraction (XRD) analysis. The method of synthesis first dissolves iodine oxide in water, creating an IO$_{3}^{-}$ solution with pH \textless 0.2. Aluminum nanoparticles are then added to the IO$_{3}^{-}$ solution and solid phase aluminum iodate hexahydrate (AIH) crystals precipitate. The bulk density of the crystalline AIH and Al composite is dependent on the initial water to aluminum concentration ratio during synthesis. Reactivity is characterized in terms of flame speed with measurements purposefully designed to capture less than 1{\%} light emission, resulting in speeds as high as 3200 m/s for AIH $+$ Al density of 3.43 g/cc. [Preview Abstract] |
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M1.00358: Structure of Water Clusters in the Presence of Acidic Defects Caitlin Bresnahan, Revati Kumar Water clusters play an important role in atmospheric processes such as gas-liquid nucleation. The presence of acidic defects in these clusters can change the free energy profile of nucleation. Molecular level insight into gas-liquid nucleation events is often not possible via experimental methods, necessitating the use of computational models. Modeling these acidic water clusters is challenging due to Grotthuss proton shuttling, the mechanism by which an excess proton hops over multiple water molecules connected via the hydrogen bond network. In order to gain an accurate molecular level interpretation of these processes and account for the physics of proton transfer and delocalization in these hydrogen bonded water clusters, reactive molecular models are required. We are developing a reactive model, based on the empirical valence bond approach, parameterized on ab initio data, to model water clusters with acidic defects like HCl. This model will be incorporated into Aggregation-Volume-Bias Monte Carlo to study nucleation in the presence of acidic defects in hydrogen bonded water clusters. The development of the model along with the results on the hydrogen bond structure and the solvation of the acidic defects, as a function of cluster size, will be presented. [Preview Abstract] |
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M1.00359: Monte Carlo / Quantum Monte Carlo study of water clusters Shiv Upadhyay, Jeffry D. Madura Water plays an important role in many physical, chemical and biological processes, however a complete description of the complex behavior of water from first principles does not exist. Much of the chemically relevant properties of water are a results of the hydrogen bond. The most common computational approach to exploring the atomic and electronic degrees of freedom of an aqueous system is Born-Oppenheimer molecular dynamics using density functional theory. The hydrogen bond is an interaction dominated by electrostatics dispersion, however dispersion plays an important role, which density functional theory fails to describe. Quantum Monte Carlo has been shown to perform well on hydrogen bonding systems, and more importantly on systems with dispersion. Here, we present our work on a Monte Carlo / Quantum Monte Carlo method to study the thermodynamic properties of water clusters. [Preview Abstract] |
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M1.00360: Structural properties of iron and nickel mixed oxide nano particles. sunil Dehipawala, Pubudu Samarasekara, Harry Gafney Small scale magnets have very high technological importance today. Instead of traditional expensive methods, scientists are exploring new low cost methods to produce micro magnets. We synthesized thin film magnets containing iron and nickel oxides. Films will be synthesized using sol-gel method and spin coating technique. Several different precursor concentrations were tested to find out the ideal concentrations for stable thin films. Structural properties of iron and nickel oxide particles were investigated using X-ray absorption and Mossbauer spectroscopy. [Preview Abstract] |
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M1.00361: INS studies of Cobalt-Copper Catalyst for the Conversion of Syngas to Higher Oxygenates Phillip Sprunger, Zi Wang, Matthew Patterson, Richard Kurtz, James Spivey Cobalt-copper catalysts have been proposed for the synthesis of ethanol and higher oxygenates as a substitute of Rh and other high-cost noble metal catalysts. Two types of sites with atomic proximity are needed to form higher oxygenates: one to dissociate CO and a second to insert CO to the intermediates to form the CH$_{\mathrm{x}}$CO intermediate. Metallic cobalt is responsible for CO dissociation, while the nature of the site for CO insertion is still under study. We have utilized inelastic neutron scattering (INS) at the VISION beamline at SNS to probe intermediate surface species of this cobalt-copper catalyst. This unique technique allows for elucidation of mechanistic details of the CO insertion and subsequent CH$_{\mathrm{x}}$CO intermediate formation on the metal surfaces (Co$^{\mathrm{0}}$, Co$_{\mathrm{2}}$C and/or Cu$^{\mathrm{0}})$. In addition to XRD and EXAFS which show a unique surface Co-C carbide formation, a combination of both INS and computational modeling indicate that the active site for CHxCO intermediates. [Preview Abstract] |
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M1.00362: Preparation of Pure and Decorated Metal Oxide Materials for Energy Applications Using Novel Chemical and Physical Deposition Methods Daniele Paradiso, Andrew Pedersen, J. Z. Larese Metal oxides (MOs) nanomaterials represent a promising route to address our nation's energy challenges. We describe the synthesis, modification and characterization of MOs (e.g. MgO , ZnO and Al$_2$O$_3$). A novel vapor based method is used to produce the MgO and ZnO materials with narrow size distribution and selective microstructure. These MO nanoparticles can be produced in sizes ranging from a few to several hundred nanometers. In addition, various phases of alumina are produced from the same native Boehmite material, are calcined at various temperatures to prepare the $\gamma$-, $\theta$- and $\alpha$- Al$_2$O$_3$ (Corundum) phases. Each of the different MO materials exhibit attractive physicochemical properties that can be employed in areas such as gas separation, carbon capture/sequestration, as well as energy storage and conversion, and catalysis. Here the interest is focused on decorating the MOs supports with small metallic nanoclusters; this avenue of interest stems directly from the widespread use of MOs as supports for highly efficient catalysts. Description of our investigations using both chemical (CVD) and physical (PVD) metal vapor deposition methods using a magnetron based system to prepare and characterize these materials will be presented. [Preview Abstract] |
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M1.00363: Energetics and Kinetics of \textit{trans}-SNARE Zippering Aleksander A. Rebane, Tong Shu, Shyam Krishnakumar, James E. Rothman, Yongli Zhang Synaptic exocytosis relies on assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins into a four-helix bundle to drive membrane fusion. Complementary SNAREs anchored to the synaptic vesicle (v-SNARE) and the plasma membrane (t-SNARE) associate from their N-termini, transiting a half-assembled intermediate (\textit{trans}-SNARE), and ending at their C-termini with a rapid power stroke that leads to membrane fusion. Although cytosolic SNARE assembly has been characterized, it remains unknown how membranes modulate the energetics and kinetics of SNARE assembly. Here, we present optical tweezers measurements on folding of single membrane proteins in phospholipid bilayers. To our knowledge, this is the first such report. We measured the energetics, kinetics, and assembly intermediates of \textit{trans}-SNAREs formed between a t-SNARE inserted into a bead-supported bilayer and a v-SNARE in a nanodisc. We found that the repulsive force of the apposed membranes increases the lifetime of the half-assembled intermediate. Our findings provide a single-molecule platform to study the regulation of \textit{trans}-SNARE assembly by proteins that act on the half-assembled state, and thus reveal the mechanistic basis of the speed and high fidelity of synaptic transmission. [Preview Abstract] |
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M1.00364: Characterizing Destructive Interference Features in Molecular Transport Junctions Panu Sam-ang, Matthew Reuter Destructive interference features in molecular electron transport have recently attracted a lot of interest due to their unconventional behavior in electronic devices. Previous analyses have developed guidelines for predicting the existence and locations of interference features, but are limited to particular classes of molecules. In this work, we build on these results to understand interference features in terms of molecular orbitals, thereby developing physical intuition for the interference features. We also provide an analysis for characterizing destructive interference features; for example, their locations and robustness. Our methodology is more general than previous analyses because it applies to a broader class of molecules than conjugated hydrocarbons, and it has the additional benefit of working with the molecular Hamiltonian (as opposed to the Green’s function). We illustrate the analysis with several molecules, including benzene, derivatives of anthraquinone, and cross-conjugated molecules. [Preview Abstract] |
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M1.00365: Ab Initio Calculation of Structural Photophysical Properties of Cytosine and Guanine Ligated Ag cluster Mohammed Jabed, Naveen Dandu, Svetlana Kilina DNA relaxed small silver is considered a promising new type of fluorophore for various application due to its exhibition of bright emission from visible to near-infrared range. Single strand DNA synthesized silver cluster has fluorescence properties and it has been shown distinct photophysical properties when linked through DNA strand and formed a dimer. Mechanism of dimer formation, electrochemical and photophysical properties of Ag cluster is still unknown. We have performed Density Functional Theory (DFT) calculations to optimize varying sizes of the silver cluster with different nucleotide ligands. We also made Ag dimer by the different mechanism and optimized by DFT method. Calculated electrochemical properties show that redox potential is dependent on the cluster size and spin state of the system as well. We have performed Time Dependent DFT (TD-DFT) for all monomer and dimer. It has shown that absorption of a monomer depends on size and charge of the cluster. On the other hand, partial replacement of cytosine by guanine could increase the intensity of lower energy band. We made conjugate bridged dimer to study any possible charge transfer nature of Ag clusters. We have found that dimer absorption could be red shifted due to conjugation bridge and size independent absorption of doublet spin system. [Preview Abstract] |
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M1.00366: Multiscale Modeling of Plasmon-Exciton Dynamics of Malachite Green Monolayers on Gold Nanoparticles Holden Smith, Tony Karam, Louis Haber, Kenneth Lopata A multi-scale hybrid quantum/classical approach using classical electrodynamics and a collection of discrete two–level quantum system is used to investigate the coupling dynamics of malachite green monolayers adsorbed to the surface of a spherical gold nanoparticle (NP). This method utilizes finite difference time domain (FDTD) to describe the plasmonic response of the NP and a two-level quantum description for the molecule via the Maxwell/Liouville equation. The molecular parameters are parameterized using CASPT2 for the energies and transition dipole moments, with the dephasing lifetime fit to experiment. This approach is suited to simulating thousands of molecules on the surface of a plasmonic NP. There is good agreement with experimental extinction measurements, predicting the plasmon and molecule depletions. Additionally, this model captures the polariton peaks overlapped with a Fano-type resonance profile observed in the experimental extinction measurements. This technique shows promise for modeling plasmon/molecule interactions in chemical sensing and light harvesting in multi-chromophore systems. [Preview Abstract] |
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M1.00367: Growth of a gold nanoparticle on TiO$_{\mathrm{2}}$ surface Pablo de la Mora, Gustavo Tavizon, Esther Agacino As it is well known gold is very unreactive, but as nanoparticle it has a strong catalytic activity. An Au small cluster is grown in the 110 surface of the TiO$_{\mathrm{2}}$ with rutile structure. Au atoms are added one by one to the surface, in each step the system is relaxed and different situations are studied. The first Au replaces an oxygen atom that forms a Ti-O-Ti bridge, the removed oxygen bonds to the closest Ti. The objective of this study is to find a cluster with a three dimensional configuration. The system was calculated with the WIEN2k package. [Preview Abstract] |
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M1.00368: The Research of Glucose Oxidation and Coating Process based on the Photophysical and Catalytic Properties of Gold Nanorods Xiaomeng Wang, Li Ma, Xiaojun Wang, Guiye Shan Gold nanomaterials have attracted many researchers attention in the area of bio sensor and bio image because of their unique property of plasmon dependent optical response characteristic. Gold nano rods show a highly dependence between their optical physical property and their size, shape, and composition. Au NRs show two strong localized plasmon resonance absorption peaks within the visible to the infrared range. Transverse surface plasmon resonance, and localized surface plasmon resonance. The LSPR peak of gold nanorods is very sensitive to the surrounding medium and the change of rods aspect ratio. The position of LSPR would change correspondingly based on the variation of surrounding medium or rods aspect ratio. Therefore, detecting the change of gold nanorods morphology as well as the reaction process is achievable by detecting the change of their LSPR peak position. Besides, due to the catalytic property of gold nano rods, new chemicals can be formed under the catalysis process of gold nanorods. Generally, it needs extreme reaction conditions for small glucose molecules to polymerize into glucan. However, specificgold nanorods can exhibit strong catalytic ability, and provide glucose a possibility to polymerize into glucan even under room temperature. [Preview Abstract] |
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M1.00369: Method for the Growth and Stabilization of Rare Earth Nano-particles Patrick Talbot, Pei-Chun Ho Quantum confinement refers to when the motion of a particle is restricted to length scales on the order of its DeBroglie wavelength, which for this project is on the order of nanometers. This confinement creates energy bands that restrict the states that the particle can exist in and this restriction manifests itself in different ways. We are interested in how this quantum confinement affects the magnetic and electrical properties of gadolinium and neodymium. However, before we can study these effects we must first develop a process to produce these rare earth nano-particles, (NPs), as well as stabilize them against the ambient environment. Rare earth metals in general have a relatively high redox potential compared to most other transition metals, and because of this require a powerful reducing agent as well as the need to be protected from the ambient environment. A growth method under development is the use of solvated electrons in tetrahydrofuran to perform the reduction [1] since electrons are one of the strongest reducing agents around. As for stabilizing these NPs against the ambient environment, we are investigating the use of surfactants to encapsulate and pacify these NPs within a micelle structure. [1]J. A. Nelson, et al., J. Am. Chem. Soc. \textbf{124} 2979 (2002). [Preview Abstract] |
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M1.00370: Ion Condensation onto Self-Assembled Nanofibers Elad Deiss-Yehiely, Julia Ortony, Baofu Qiao, Samuel Stupp, Monica Olvera de la Cruz Self-assembled peptide amphiphile (PA) nanofibers are a class of supramolecular materials with promising applications in nanotechnology. Alignment of nanofibers, which is essential for biomaterials applications, is achieved by introducing salts to PA nanofiber suspensions. Regardless of its importance, the effect of ion concentrations on the porperties of these nanostructures remains unexplored. Using atomistic molecular dynamics simulations, canonical PA nanostructures are investigated in order to elucidate the relationship between counterion condensation and morphological changes. Simulations reveal that nanofibers with the highest density cross-section have expanded radii. This expansion decreases the accessible volume for sodium counterions and diminishes the counterion translational entropy, while also reducing the total electrostatic potential. Interestingly, we show that the competition between these effects leads to a fraction of condensed counterions independent of the fiber radius. [Preview Abstract] |
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M1.00371: Phase Transition Properties of Ferroelectric Ammonium Sulfate Dispersed in Mesoporous Silica Ozge Gunaydin-Sen, Ramanjaneyulu Seemaladinne, Krishna Kharel Ammonium Sulfate, (NH$_{\mathrm{4}})_{\mathrm{2}}$SO$_{\mathrm{4}}$ (AS), a model ferroelectric, exhibits a structural phase transition at around 223 K. Recently, the dimensional downscaling of the ferroelectric materials (nanostructured ferroelectrics) led to the development and improvement of many electronic devices. Nanoscaling ferroelectric materials change many structural properties such as phase transition temperatures and dielectric constant as a result of size effect and interaction with the pore walls. We investigated thermal properties of bulk AS and after dispersing it in nanoporous silica, MCM-41. The heat capacity measurements over a temperature range of 180--300 K displayed an anomaly at around 223 K for AS, indicating a first-order structural phase transition. The transition enthalphy and entropy quantities were investigated for the bulk and the nanosized AS. Variable temperature infrared respose will also be discussed to further understand the phase transition mechanism in detail for the bulk and the nanocomposites. [Preview Abstract] |
(Author Not Attending)
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M1.00372: Endohedral fullerenes contaning transition-metal clusters Shusil Bhusal, Luis Basurto, Rajendra Zope, Tunna Baruah We report detailed investigation of structural, electronic, and spectroscopic properties of VSc$_2$N-containing fullerenes in the size range C$_{68}$ - C$_{96}$. First, the candidate structures of the ground state are obtained using a systematic approach in which a large number of isomers of endohedral fullerenes were screened for their energetic stability. Stability of some of the most promising isomers were further studied using density functional theory at the all-electron level using large polarized Gaussian basis sets. The effect of the V doping is examined on the structure, spin states and the magnetic properties of the endohedral fullerenes. [Preview Abstract] |
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M1.00373: Preparation and Structural Studies on Hybrid Core-Shell Nanoparticles Consisting of Silica Core and Conjugated Block Copolymer Shell Prepared by Surface-Initiated Polymerization Sourav Chatterjee, Tony Karam, Cornelia Rosu, Xin Li, Changwoo Do, Sang Gil Youm, Louis Haber, Paul Russo, Evgueni Nesterov Controlled Kumada catalyst-transfer polymerization occurring by chain-growth mechanism was developed for the synthesis of conjugated polymers and block copolymers from the surface of inorganic substrates such as silica nanoparticles. Although synthesis of conjugated polymers via Kumada polymerization became an established method for solution polymerization, carrying out the same reaction in heterogeneous conditions to form monodisperse polymer chains still remains a challenge. We developed and described a simple and efficient approach to the preparation of surface-immobilized layer of catalytic Ni(II) initiator, and demonstrated using it to prepare polymers and block copolymers on silica nanoparticle. The structure of the resulting hybrid nanostructures was thoroughly studied using small-angle neutron and X-ray scattering, thermal analysis, and optical spectroscopy. The photoexcitation energy transfer processes in the conjugated polymer shell were studied via steady-state and time resolved transient absorption spectroscopy. This study uncovered important details of the energy transfer, which will be discussed in this presentation. [Preview Abstract] |
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M1.00374: A energy-accuracy tradeoff in the physics of cellular sensing Sarah Harvey, Subhaneil Lahiri, Surya Ganguli Single cells are capable of complex information processing about their environment, particularly in the form of highly accurate external concentration sensing. The fundamental limit of this accuracy set by diffusion has been studied since the 1977 Berg-Purcell limit, however, thermodynamic constraints on the design of these sensors have remained theoretically obscure. We derive energy-accuracy tradeoffs in nonequilibrium molecular processes underlying cellular sensing receptors using stochastic thermodynamics. These receptor systems are often modeled as arbitrary continuous time Markov networks, with an external signal modulating the transition rates. We derive a fundamental limit on sensing accuracy by calculating the Fisher information for a Markov chain trajectory with respect to an external signal, and then consider more biophysically plausible systems with large deviation theory. These lower bounds, confirmed by numerical simulations, reveal a tradeoff when the network is driven out of equilibrium between the power dissipated by the system, the sensing accuracy, and the observation time. Moreover, the classic Berg-Purcell limit is reproduced at equilibrium. Overall, our work reveals fundamental thermodynamic limits on sensing accuracy for any Markovian signaling system. [Preview Abstract] |
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M1.00375: Modeling the dynamics of shape generation and sensing by proteins on lipid membranes Nikhil Walani, Marino Arroyo Lipid membranes are fluid surfaces with flexural resistance that interact with proteins to perform their function in a biological context. A set of these proteins are responsible for shaping the lipid membranes, or of sensing curvature. A large body of work has examined the curvature sensing and generation properties of these proteins. Even though such processes are fundamentally dynamical in cells and in in vitro reconstituted systems, theoretical and computational studies have largely focussed on equilibrium thermodynamics. In this work, we propose a theoretical framework based on Onsager's variational principle of irreversible thermodynamics that captures the dynamics of adsorption, diffusion, and shape generation or sensing of proteins on lipid surfaces. [Preview Abstract] |
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M1.00376: Abstract Withdrawn
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M1.00377: Thermo-optical Modelling of Laser Matter Interactions in Selective Laser Melting Processes. Raj Vinnakota, Dentcho Genov Selective laser melting (SLM) is one of the promising advanced manufacturing techniques, which is providing an ideal platform to manufacture components with zero geometric constraints. Coupling the electromagnetic and thermodynamic processes involved in the SLM, and developing the comprehensive theoretical model of the same is of great importance since it can provide significant improvements in the printing processes by revealing the optimal parametric space related to applied laser power, scan velocity, powder material, layer thickness and porosity. Here, we present a self-consistent Thermo-optical model which simultaneously solves the Maxwell's and the heat transfer equations and provides an insight into the electromagnetic energy released in the powder-beds and the concurrent thermodynamics of the particles temperature rise and onset of melting. The numerical calculations are compared with developed analytical model of the SLM process providing insight into the dynamics between laser facilitated Joule heating and radiation mitigated rise in temperature. These results provide guidelines toward improved energy efficiency and optimization of the SLM process scan rates. [Preview Abstract] |
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M1.00378: Are The Chemical Bonding Interactions in Halide Perovskite Solar Cells Cooperative? Pradeep Varadwaj, Arpita Varadwaj, Koichi Yamashita Designing novel photo-sensitive and --responsive light harvesting solar cell materials is an important area of nanoscience and technologies mainly because these can transform the light energy directly or indirectly into electricity. Examples of a few of them, \textit{inter alia}, include dye-sensitized solar cells, organic solar cells and halide perovskite solar cells. Methylammonium lead iodide (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}})$ organic-inorganic hybrid perovskite is one of the highly valued photocatalysts reported till date, which is comparable in its strength with the inorganic cesium lead iodide (CsPbI$_{\mathrm{3}})$ perovskite solar cell especially for energy conversion. The study thus has focused on the fundamental understanding of the geometrical, electronic and energetic properties of the CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ and CsPbI$_{\mathrm{3}}$ nanoclusters, obtained using density functional theory calculations. The main aim towards this end was to uncover the consequences of additivity, or non-additive cooperative binding, in the intermolecular chemical bonding interactions examined for these nanoclusters. The results obtained are compared with the current state-of-the-art, and will be discussed in detail. [Preview Abstract] |
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M1.00379: Using the Binary Phase-Field Crystal Model to Describe Non-Classical Nucleation Pathways in Gold Nanoparticles Nathan Smith, Nikolas Provatas Recent experimental work [Loh et al, Nature Chemistry, Vol 9, 2017] has shown that gold nanoparticles can precipitate from an aqueous solution through a non-classical, multi-step nucleation process. This multi-step process begins with spinodal decomposition into solute-rich and solute-poor liquid domains followed by nucleation from within the solute-rich domains. We present a binary phase-field crystal theory that shows the same phenomology and examine various cross-over regimes in the growth and coarsening of liquid and solid domains. [Preview Abstract] |
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M1.00380: Anisotropic behavior of superconductivity in FeSe$_{\mathrm{0.5}}$Te$_{\mathrm{0.5}}$ thin films. Tong Wang, Zhongwen Xing The resistive properties under angle-dependent magnetic fields up to 16 Tesla are investigated in superconducting FeTe$_{\mathrm{0.5}}$Se$_{\mathrm{0.5}}$ (FST) thin films grown on SrTiO$_{\mathrm{3}}$ (STO) substrates without or with a buffered CeO$_{\mathrm{2}}$ film. It is found that the FST/CeO$_{\mathrm{2}}$/STO films have an enhanced superconducting transition temperature and an induced superconducting anisotropy in comparison with the FST/STO films. These different behaviors in the absence and presence of the buffered CeO$_{\mathrm{2}}$ film are attributed to the change of the out-of-plane lattice constant, rather than the change of Se/Te heights within the tetrahedron. [Preview Abstract] |
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M1.00381: Mesoscale Thermodynamically motivated Statistical Mechanics based Kinetic Model for Sintering monoliths Nisha Mohan Modeling the evolution of microstructure during sintering is a persistent challenge in ceramics science, although needed as the microstructure impacts properties of an engineered material. Bridging the gap between microscopic and continuum models, kinetic Monte Carlo (kMC) methods provide a stochastic approach towards sintering and microstructure evolution. These kMC models work at the mesoscale, with length and time-scales between those of atomistic and continuum approaches. We develop a sintering/compacting model for the two-phase sintering of boron nitride ceramics and allotropes alike. Our formulation includes mechanisms for phase transformation between h-BN and c-BN and takes into account thermodynamics of pressure and temperature on interaction energies and mechanism rates. In addition to replicating the micro-structure evolution observed in experiments, it also captures the phase diagram of Boron Nitride materials. Results have been analyzed in terms of phase diagrams and crystal growth. It also serves with insights to guide the choice of additives and conditions for the sintering process.While detailed time and spatial resolutions are lost in any MC, the progression of stochastic events still captures plausible local energy minima and long-time temporal developments. [Preview Abstract] |
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M1.00382: Channeling Polyolefin Molecular Structure - Bulk Property Correlation Strategies for Industrial Applicability Rohan Hule, Derek Thurman, Antonios Doufas Polyolefins occupy a significant volume of the polymer products portfolio in commodity and high value applications. Quantifying and optimizing structure-property relationships enables growth in new markets. It is well recognized that coupling lab-based, comprehensive methodologies with bulk properties of interest to industrial environments offer the greatest potential of technology advancement, ultimately leading to commercial success. It is imperative to recognize the existing gap of knowledge translation between lab measurements and industrial-scale operability. This study highlights experimental HDPEs synthesized from dual, single-site, co-supported catalysts that exhibit enhanced solid-state properties such as stiffness, impact and ESCR surpassing conventional trends. Commercial resins across distinct sub-families were included as well. Commonality amongst these resins is bimodality and broad MW distribution with well-defined splits and spreads. Investigations on commercially relevant parameters such as melt strength, melt elasticity and shear thinning established excellent performance for experimental bimodals, corroborating potential benefits compared to commercial HDPEs. To summarize, the effort highlights well-recognized pathways such as improvements in mechanical and melt properties that can be attributed to apposite tuning of polymer chain architecture and MW distribution with implications across myriad markets. Ultimately, this may serve as a pathway for producing innovative products that deliver business success and growth. [Preview Abstract] |
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M1.00383: Measurement of the Structure and Molecular Dynamics of Ionic Solutions for Redox Flow Battery Zhixia Li, Lily Robertson, Jeffery Moore, Yang Zhang Redox flow battery (RFB) is a promising electrical energy storage technology with great potential to finally realize alternative energy sources for the next-generation vehicles and at grid scales. The design of RFB is unique as the power scales separately from the energy capacity. The latter depends on the size of storage tanks and the concentration of the active materials. Redox-active organic molecules are excellent candidates with high synthetic tunability for both redox properties as well as, importantly, solubility. However, upon increasing concentrations, the flow cell has less cycling stability and more capacity fade. Further, after charging the battery, the viscosity increases while the ionic conductivity decreases, and thus the cell becomes overall ineffective. To understand the mechanism of the increased viscosity, we performed differential scanning calorimetry, wide and small angle X-rays scattering, and quasi-elastic neutron scattering measurements. Herein, we will present the measurement results and relative analysis. [Preview Abstract] |
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M1.00384: Opinion Dynamics on Networks with Inference of Unobservable States of Others Ryo Fujie In most opinion formation models which have been proposed, the agents decide their states (i.e. opinions) by referring to the states of others. However, the referred states of others are not necessarily observable and may be inferred. To investigate the effect of an inference of the states of others on opinion dynamics, I propose an extended voter model on networks where observable and referable node sets are different. These sets for a node defined as the nearest to the $m_o$-th neighbors for observable nodes and the nearest to the $m_r$-th neighbors for referable nodes. The state of referable but unobservable node which is the $m$-th neighbor ($m_o< m\le m_r$) is inferred by using the observed or inferred states of the ($m-1$)-th neighbors. In the case of $m_o=1$ and $m_r=N$, I show analytically that the linear superposition of the states weighted by ``betweenness pagerank'' is conserved. This conserved quantity coincides with the fixation probability. On the other hand, in the case of $m_o=m_r=1$, the model comes down to the standard voter model on networks and the conserved quantity is a degree-weighted superposition of the states. Thus, the introduction of the inference changes the important opinion spreaders from the high-degree nodes to the high-betweenness pagerank nodes. [Preview Abstract] |
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M1.00385: Morphology of Block Copolymer Electrolytes: A Numerical Self-Consistent Field Theory Study Kevin Hou, Jian Qin Engineering the morphology of ion-containing block copolymers is imperative for the optimization of their charge-transport and mechanical properties. Existing experiments have demonstrated that the addition of ions has a dramatic effect on the morphology and thermodynamic behavior of these structured electrolytes. We have developed an efficient, symmetry-adapted algorithm to calculate the ionic interactions in the SCFT for ion-containing polymers. We present the results of a numerical SCFT study examining how dielectric heterogeneity, ion concentration, and ion solvation affect morphology, domain spacing, ion distribution, and polymer density profiles. Particular attention is given to the detailed morphological analysis of the bicontinuous gyroidal phase, as well as the relevance of the aforementioned results to ionic conductivity. [Preview Abstract] |
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M1.00386: Recent advancements in nanoscale IR spectroscopy for materials science Eoghan Dillon, Honghua Yang, Kevin Kjoller This talk will focus on the advances in measuring the chemical and optical properties of materials with nanometer scale spatial resolution. Conventional infrared spectroscopy is one of the most widely used tools for chemical analysis, but optical diffraction limits its spatial resolution to the scale of many microns. Atomic force microscopy (AFM) enjoys excellent spatial resolution, but has historically lacked the ability to perform robust chemical analysis. This presentation will discuss the advances in two techniques (1) AFM-based infrared spectroscopy (AFM-IR) and (2) scattering scanning near field optical microscopy (s-SNOM). Both of these techniques overcome the diffraction limit, providing the ability to measure and map chemical and optical properties with ~ 10 nanometer spatial resolution. Recent advances including Tapping AFM-IR and increases in laser sweep rates have significantly improved the resolution and sensitivity of AFM-IR. As complementary techniques, AFM-IR and s-SNOM together provide an unrivaled capability to perform nanoscale chemical analysis on a diverse range of organic, inorganic, photonic and electronic materials. This talk will focus on AFM and s-SNOM applications on samples from fields including polymers, life sciences, graphene and nanoantennas. [Preview Abstract] |
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M1.00387: Mossbauer Study of Low Temperature Magnetic and magnetooptic Properties of Amorphous Tb/Fe Multilayers Ataur Chowdhury Magnetic and magnetooptic properties of multilayers critically depend on detailed magnetic and structural ordering of the interface. To study these properties in Tb/Fe multilayers, samples with varying layer thicknesses were fabricated by planar magnetic sputtering on polyester substrates. Mossbauer effect spectra were recorded at different temperatures ranging between 20 K and 300 K. The results show that perpendicular magnetic anisotropy (PMA) increases as temperature decreases for samples that show parallel anisotropy at room temperature, and for samples that show strong PMA at room temperature, no significant change in PMA is observed at low temperature (\textless 100 K). Hyperfine field of samples that display parallel anisotropy at room temperature shows oscillatory behavior, reminiscent of RKKY oscillations, at low temperatures (\textless 100 K). Plausible causes of these properties will be discussed in the paper. [Preview Abstract] |
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M1.00388: Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire. Manuel Munguía Rodríguez, Ricardo Betancourt Riera, René Betancourt Riera, Raúl Riera Aroche, Rodrigo Rosas Burgos The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire are calculated, and expressions for the electronic states are presented. The system is modeled by considering T$=$0K and also a single parabolic conduction band, which is split into a subbands system due to the confinement in the wire. The gain and differential cross-section for an electron Raman scattering process are obtained. Also, the emission spectra for several scattering configurations are discussed, and the interpretation of the singularities found in the spectra are given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers systems. [Preview Abstract] |
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M1.00389: Thermoelectricity in Non-Periodically Segmented and Branched Nanowires: A Real-Space Renormalization Approach Jose Eduardo Gonzalez, Vicenta Sanchez, Chumin Wang The direct conversion between thermal and electrical energies by thermoelectric low-dimensional devices has become an important alternative, whose efficiency is determined by the dimensionless figure-of-merit defined as $ZT={\sigma S^{2}T} \mathord{\left/ {\vphantom {{\sigma S^{2}T} {(\kappa _{el} +\kappa_{ph} )}}} \right. \kern-\nulldelimiterspace} {(\kappa_{el} +\kappa_{ph} )}$, where the Seebeck coefficient ($S)$, electrical conductivity ($\sigma )$, electronic ($\kappa_{el})$ and phononic ($\kappa_{ph})$ thermal conductivities have an inherent correlation making difficult to improve ZT. In this work, we study thermoelectric properties of periodic and quasiperiodically segmented and branched nanowires by means of a real-space renormalization plus convolution method [1] developed for the Kubo-Greenwood formula, in which tight-binding and Born models are respectively used for the calculation of electric and lattice thermal conductivities. This method has the advantage of being computationally efficient, without introducing additional approximations, and capable to analyze aperiodic nanowires with truly macroscopic length. Analytical results are found for periodic nanowires showing a maximum ZT in the temperature space, as occurred in the carrier concentration one. Moreover, the quasiperiodicity seems to be an important ZT enhancing factor [2], since it significantly diminishes the thermal conduction at low temperature of long wavelength acoustic phonons which do not feel local defects neither impurities. [1] V. Sanchez and C. Wang, Phys. Rev. B 70, 144207 (2004). [2] J. E. Gonzalez, V. Sanchez, and C. Wang, J. Electron. Mater. (2017) doi: 10.1007/s11664-016-4946-y [Preview Abstract] |
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M1.00390: Enhanced quantum coherence in graphene by plasmon coupling Laiming Wei, Guanghui Cheng, Meng-Hsien Lin, Wei Qin, Xiaodong Fan, Huayang Zhang, Shangjr Gwo, J. G. Hou, Zhenyu Zhang, Changgan Zeng The quantum coherence plays a crucial role in solid-state quantum computation. Here we report a substantial enhancement of quantum coherence in graphene in proximity to Au nanoparticles with the excitation of Au plasmons under laser illumination, as evidenced by the weak localization characterizations at low temperatures. This effect is more prominent with increasing laser power and decreasing temperature, whereas the optical doping in the graphene is negligible. The enhanced quantum coherence could be attributed to the suppression of electron-electron dephasing by electron-plasmon coupling. Our findings may provide insights into the design of graphene-based quantum device controlled by plasmons. [Preview Abstract] |
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M1.00391: Hydration Structures and Water Chemistry at Zirconia-Water Interfaces Binyang Hou, Changyong Park, Seunghyun Kim, Taeho Kim, Ji Hyun Kim, Jongjin Kim, Seungbum Hong, Chi Bum Bahn Zirconia is an important material in numerous applications, such as gas sensors, solid oxide fuel cell electrolytes, and bio-medical materials. It also plays a key role on protecting zirconium alloys in highly corrosive environments found in pressurized water reactors. The degradation of the metal/oxide is primarily due to the interactions of surface oxide with water. Here we study the interactions of zirconia with water in terms of interfacial hydration structures at the 8 mol{\%} yttria-stabilized zirconia (YSZ) surfaces using synchrotron-based X-ray reflectivity techniques. Interfacial hydration structures on three crystallographic orientations were determined with sub-angstrom resolution and compared with each other to identify common features and different surface chemistry effects on the interfacial processes. Meanwhile, zinc injection into the reactor coolant system has been known to be effective in both reducing radioactive wastes and stabilizing crud oxide layers of the metal alloys. We also studied the effect of zinc adsorption on the interfacial hydration structures of YSZs. Our X-ray reflectivity data reveal obvious hydration structure changes at (100) and (111) surfaces, but only minor changes at (110) surface. We further confirmed the detailed element specific adsorption profiles of Zn$^{\mathrm{2+}}$ ions near (110) and (111) surfaces with resonant anomalous X-ray reflectivity measurements. [Preview Abstract] |
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M1.00392: Ni-DNA based Y shape nanowire device development and characterization Wen-Hung Wang, Ya-Hui Lin, Chung-Hao Yang, Yi Chen, Wen-Bin Jian, Chia-Ching Chang Owing to the good charge transport and self-assembly property of Ni-DNA, it becomes one of the most promising one-dimensional conducting nanowire. Two-terminal Ni ions doping DNA (Ni-DNA) nanowire devices have been developed and characterized recently. It is of interest to understand the charge transport behavior in a Yshape Ni-DNA device. In this study Yshape Ni-DNA has been synthesized and the DNA is linked on a three-terminal nanodevice via selfassembled process. The $I-V$ curves of Yshape Ni-DNA indicated that this device exhibits negative differential resistance spectra between each two terminals. The further charge transport behavior and mechanism will be revealed in this study.\\ \\Keywords: DNA, Y-shape Ni-DNA, negative differential resistance [Preview Abstract] |
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M1.00393: Optimization of Ionization-potential Improved Range-separated Density Functional Theory Yifan Jin, Rodney Bartlett The physical meaning of the Kohn-Sham eigenvalues is traditionally not quite clear. But it is essential for the density functional theory, which is usually designed empirically, to converge to the right answer. The currently developed range-separated density functional methods in the QTP family, that is, the CAM-QTP00 and CAM-QTP01, are designed to make the Kohn-Sham eigenvalues of all the occupied orbitals good approximation to the exact ionization energies. The benchmark calculations have shown that these methods, especially the CAM-QTP01, could improve the ionization and excitation energies along with the chemical and physical properties of the ground states. However, they still could not well reproduce certain properties such as the atomization energies of the large organic molecules. During the recent work, the methods were further optimized with larger training sets and new algorithm. And the accuracy of those ground and excited states properties was further improved. The basic principles, strategy of functional optimization and the benchmark results will be presented. [Preview Abstract] |
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M1.00394: Probing the topological superconductivity in helical metal: a quantum magnetic impurity Rui Wang, Baigeng Wang, Dingyu Xing The Kondo problem in superconducting topological insulator surface (STIS) is investigated. Different from the traditional Kondo physics in convention superconductor, a pseudo Kondo singlet state is revealed, which is the singlet states formed by the local magnetic moment and a complex pseudo spin composed of both the real spin and orbital angular momentum components. Rich in-gap physics is found, due to the competition between Bardeen-Schrieffer-Cooper singlet and the pseudo Kondo singlet. Remarkably, it is proved that the quantum magnetic impurity is only coupled to half of the degrees of freedom in STIS, and therefore the topological superconductivity remains robust and perfectly preserves the superconductor coherent peaks. These findings are unique in STIS, indicating that the quantum magnetic impurity can be used as an effective method to distinguish different types of topological superconductivity. [Preview Abstract] |
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M1.00395: Integrative interactive visualization of crystal structure, band structure, and Brillouin zone Robert Hanson, Ben Hinke, Matthew Van Koevering, Corey Oses, Cormac Toher, David Hicks, Eric Gossett, Jose Plata Ramos, Stefano Curtarolo The AFLOW library is an open-access database for high throughput ab-initio calculations that serves as a resource for the dissemination of computational results in the area of materials science. Our project aims to create an interactive web-based visualization of any structure in the AFLOW database that has associate band structure data in a way that allows novel simultaneous exploration of the crystal structure, band structure, and Brillouin zone. Interactivity is obtained using two synchronized JSmol implementations, one for the crystal structure and one for the Brillouin zone, along with a D3-based band-structure diagram produced on the fly from data obtained from the AFLOW database. The current website portal (http://aflowlib.mems.duke.edu/users/jmolers/matt/website) allows interactive access and visualization of crystal structure, Brillouin zone and band structure for more than 55,000 inorganic crystal structures. [Preview Abstract] |
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M1.00396: Study on the Role of Biochemical Fullerene Derivatives in Treating Tumor Cells Ji Han Yoon, Gene Park, Joseph Shin Substituted fullerenes tagged with a functionalized group or an antibody such as an organic functional group can target cancer cells. In this paper, we compared the molecular energy of fullerenes doped with clusters such as hydroxyl(OH), carboxyl(COOH), and malonic acid(C-COOH) derivatives When comparing BB derivatives (BB7, BB8, BB9) on C40 and C72 fullerene models, C72 derivatives were observed to have much lower optimization energy levels (kJ/mol) than derivatives of C40. Although the C72 BB derivatives may have a larger number of carbon atoms than the C40 BB derivatives, the C72 BB derivatives possess a more spherical shape, which yields to lower enthalpy. Thus, within the BB derivatives of C40/C72 fullerenes, the phenomenon of C72 models having overall lower optimization energy can be attributed to the C72 models’ rather spherical and stable shape. When comparing hydroxyl (OH), carboxyl (COOH), and C-COOH derivatives on C40 fullerene models, carboxyl derivatives were observed to have much lower progressing optimization energy levels (kJ/mol) than those of hydroxyl derivatives, with hydroxyl derivatives having much lower progressing optimization energy levels than those of C-COOH derivatives. [Preview Abstract] |
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M1.00397: Untangling the cerium and iron contributions to the magnetism of Ce-doped yttrium iron garnet G. Herranz, B. Casals, R. Cichelero, J. Fontcuberta, H.B. Vasili, P. Gargiani, M. Valvidares, J. Herrero-Martin, E. Pellegrin, J. Geshev Due to their large magneto-optic responses, rare-earth-doped yttrium iron garnets, Y$_{3}$Fe$_{5}$O$_{12}$ (YIG), are highly regarded for their potential in photonics and magnonics. Here we consider the case of Ce-doped YIG (Ce-YIG), in which substitutional Ce$^{3+}$ ions are magnetic because of their 4f$^{1}$ ground state. Hence, it is expected that Ce substitution can remarkably impact on the magnetization of YIG. However, it is not completely understood how exactly the Ce ions contribute to the macroscopic magnetic properties. Having this in mind, we have carried out magneto-optical and soft x-ray spectroscopy measurements on Ce-YIG thin films. In particular, we have used the element-specificity of XMCD to extract the individual magnetic hysteresis loops linked to Ce$^{3+}$ and Fe$^{3+}$ ions, respectively. Our results show that the doping of YIG with Ce causes a disruption of the electronic and magnetic properties of the parent compound, which results into a reduction of the magnetic coupling between the Ce and Fe magnetic moments, especially at low magnetic fields. Our results are relevant for the understanding of magnetism in rare-earth doped YIG and, eventually, may enable a quantitative evaluation of the magneto-optic properties of rare earth incorporation into YIG. [Preview Abstract] |
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M1.00398: Tungsten Oxide Thin Films Fabricated using Femtosecond and Nanosecond Pulsed Laser Deposition Anthony Pelton, Robert Mayanovic Pulsed laser deposition (PLD) is a promising technique for creating inexpensive, nanostructured tungsten oxide thin films which may be suitable for photocatalysis, electrochromic devices and fuel cell electrodes. We have prepared tungsten oxide thin films by using a pulsed femtosecond laser or an excimer (nanosecond) pulsed laser. The PLD Na-incorporated WO$_{\mathrm{3}}$-based films were deposited on glass and silicon substrates. After deposition, the thin films were annealed to 550 $^{\circ}$ C up to 30 hours in air. The films were characterized using SEM, XRD, Raman Spectroscopy, and XPS, both before and after annealing. Prior to annealing, the Na$_{\mathrm{x}}$WO$_{\mathrm{3\thinspace }}$films made using the femtosecond PLD (f-PLD) are rougher and display more texture than the films grown using nanosecond PLD (n-PLD). Before annealing, the f-PLD films exhibit both 3-D nano-crystalline and amorphous structures, whereas the n-PLD films are smoother and predominately amorphous before annealing. The post-annealed Na$_{\mathrm{x}}$WO$_{\mathrm{3\thinspace }}$films show evidence of having several structural phases, including monoclinic, orthorhombic, triclinic and hexagonal; the orthorhombic and hexagonal phases are most likely tungsten bronzes. [Preview Abstract] |
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M1.00399: Thermoelectric properties of SnSe$_{\mathbf{1-x}}$\textbf{S}$_{\mathbf{x\, }}$\textbf{(0 \textless x }$\le $\textbf{ 1) single crystals} Thi Minh Hai Nguyen, Anh Tuan Duong, Ganbat Duvjir, Thi Ly Trinh, Van Quang Nguyen, Jungdae Kim, Sunglae Cho Tin selenide (SnSe), a p-type semiconductor, has attracted many attention due to its excellent thermoelectric efficiency, i.e., ZT $=$ 2.6 along the b-axis of its high temperature phase. This issue has renewed interests in thermoelectric properties of the materials which adopted the same layered structure as SnSe, such as SnS, GeS, and GeSe. Among these compounds, tin (II) sulfide (SnS) is exceptionally attractive because of its natural abundance and low toxicity. However, the experimental results show that SnS has possessed a small value of the figure of merit. To optimize the thermoelectric performance of SnS, making solid solution is a potential way. That is our motivation for the investigation of SnSe$_{1-x}$S$_{x}$ single crystals' thermoelectric properties. In this study, SnSe$_{1-x}$S$_{x}$ (0 \textless x $\le $ 1) single crystals were fabricated using the temperature gradient method. The crystal structure was investigated by SEM and XRD, which indicated that fabricated SnSe$_{1-x}$S$_{x}$ single crystals have layered structure with lattice constants change gradually following Vegard's law. Transport properties were synthesized by physical properties measurement system (PPMS). We observed that for x $=$ 0.2, SnSe$_{0.8}$S$_{0.2}$, electrical resistivity and Seebeck coefficient were 0.52 $\Omega \cdot $cm and 639.36 $\mu $VK$^{-1}$ at 270 K, respectively, which resulted in the power factor of 0.78 $\mu $WK$^{-2}$cm$^{-1}$. Furthermore, we will discuss about the thermal conductivity and microscopic surface structure of these samples. [Preview Abstract] |
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M1.00400: Energy Dissipation when Internal Wave Beams Reflect from a Slope John Daniel, Bruce Rodenborn Internal waves propagate in the bulk of the ocean because it has a vertically varying density profile. These waves may be important in determining the global ocean circulation patterns because they redistribute tidal energy. Reflection of internal waves from a uniform sloping boundary is often analyzed using linear or a weakly nonlinear inviscid theory. Under these assumptions for a linearly stratified fluid, Tabaei et al. (J. Fluid Mech. 526, 2005) predicted the partitioning of energy between the reflected and second harmonic waves. We previously conducted experiments and simulations that tested these theories (Rodenborn et. al., Phys. Fluids, 2011). In the previous study, we used integrated kinetic energy as a measure of beam energy. We compare previous results with a method using energy flux determined from the velocity and pressure fields. We also calculate the rate at which energy is dissipated in the reflection process by finding the energy flux into and out of a surface above the reflection region $E_{out}/E_{in}$. We find high rates of energy dissipation $O$(90\%) even for weakly nonlinear wave beams and with the viscosity reduced by an order of magnitude, which implies dissipation may be relevant to internal wave reflection in the ocean. [Preview Abstract] |
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M1.00401: Forensic Science Research and Development at the National Institute of Justice: Opportunities in Applied Physics Gregory Dutton Forensic science is a collection of applied disciplines that draws from all branches of science. A key question in forensic analysis is: to what degree do a piece of evidence and a known reference sample share characteristics? Quantification of similarity, estimation of uncertainty, and determination of relevant population statistics are of current concern. A 2016 PCAST report questioned the foundational validity and the validity in practice of several forensic disciplines, including latent fingerprints, firearms comparisons and DNA mixture interpretation. One recommendation was the advancement of objective, automated comparison methods based on image analysis and machine learning. These concerns parallel the National Institute of Justice's ongoing R{\&}D investments in applied chemistry, biology and physics. NIJ maintains a funding program spanning fundamental research with potential for forensic application to the validation of novel instruments and methods. Since 2009, NIJ has funded over {\$}179M in external research to support the advancement of accuracy, validity and efficiency in the forensic sciences. An overview of NIJ's programs will be presented, with examples of relevant projects from fluid dynamics, 3D imaging, acoustics, and materials science. [Preview Abstract] |
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