Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L70: Poster Session II (11:15am-2:15pm)Poster
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Room: BCEC Exhibit Hall |
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L70.00001: POLYMER PHYSICS
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L70.00002: Thermal Properties of Polyvinyl Alcohol by Fast Scanning Calorimetry David Thomas, Evgeny Zhuravlev, Andreas Wurm, Christoph Schick, Peggy Cebe Polyvinyl alcohol crystallizes from the melt so rapidly that it is difficult to obtain fully amorphous glassy polymer. To study thermal properties of fully amorphous PVA, we use fast scanning calorimetry (FSC) to heat and cool at rates ranging from 1000 K/s up to 600,000 K/s. We determine the critical cooling rate, βc, needed to quench PVA from the melt into an amorphous glass as |βc| = 20,000 K/s. Using FSC in combination with conventional differential scanning calorimetry (DSC), we evaluate the temperature dependent liquid state heat capacity, cpLiquid(T) = ((0.0016 ± 0.0002)* T + (2.3 ± 0.2)) J/(gK). The specific heat capacity increment at Tg for fully amorphous PVA is Δcpamor(Tg) = (1.005 ± 0.002) J/(gK). For the semi-crystalline samples used in this study, PVA obeys a two phase model in which the rigid amorphous fraction, φRA ~ 0. The approaches used in this work are applicable to any semicrystalline polymer or biopolymer which degrades upon heating, or crystallizes so rapidly from the melt that a fully amorphous material cannot be realized at conventional DSC rates. |
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L70.00003: A new concept of electrodes for ambipolar carrier injection in organic
semiconductors Katsumi Tanigaki, Thangavel Kanagasekaran, Syun Onuki, Taiki Miura, Hidekazu Shimotani Organic semiconductors (OSCs) have attracted much attention for low cost, flexible and human friendly optoelectronics. However, achieving high electron injection efficiency is difficult from air stable electrodes and cannot be equivalent to that of holes. Here, we present a novel concept of electrode composed of a bilayer of tetratetracontane (TTC) and polycrystalline organic semiconductors (pcOSC) covered by a metal (M) thin film layer. Field effect transistors of single crystal organic semiconductors (scOSCs) with the new electrodes of M/pcOSC/TTC (M: Ca or Au) show both highly efficient electron and hole injection. Contact resistances of electron and hole injection from Ca/pcOSC/TTC and Au/pcOSC/TTC are fascinatingly lower than those from pure Ca for electrons and Au for holes, respectively. Equivalent high field effect mobilities of holes (22 cm2V–1s–1) and electrons (5.0 cm2V–1s–1) can be observed in a rubrene single crystal, which are the highest among field effect transistors so far proposed. Higly efficient light emission will be demonstrated via amipolar carrier injection. |
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L70.00004: Water-Mediated Mixed Ionic-Electronic Conduction in Polythiophene-Derived Polyelectrolytes Garrett Grocke, Ban Dong, Shrayesh Patel Conjugated polyelectrolytes that can conduct both ionically and electronically are attractive candidates for next-generation electrochemical devices, yet little is known about the impact of polymer processing and morphology on mixed conduction characteristics. This work reports the influence of water on the structure and conduction of poly[3-(potassium-n-alkanoate) thiophene-2,5-diyl]s (P3KnTs) in thin film. These materials were found to be highly resistive under anhydrous conditions but exhibited mixed ion-electron conduction as a function of increasing relative humidity. UV-Vis-NIR measurements provide evidence for water-assisted formation of alkanoate-anion-stabilized polythiophene bipolaron states and thus electronic conductivity, wherein dissociation of potassium-alkanoate bonds leads to the enhanced ionic conductivity. Additionally, using in-situ humidified scattering experiments, it was shown that increasing side-chain stacking distance coincides with the improvement in ionic conductivity as a function of relative humidity, suggesting that ionic transport occurs through regular pathways formed by the flexible side-chains. Our results show strong influence of water on mixed ion-electron conduction characteristics of conjugated polyelectrolytes in undoped conditions. |
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L70.00005: Charge transport and structural properties of functionally graded conjugated polymer thin films for organic thermoelectrics Tengzhou Ma, Mark DiTusa, Ban Dong, Garrett Grocke, Shrayesh Patel Semiconducting polymers demonstrate great potential for low-cost, light-weight, and flexible organic electronic devices such as field-effect transistors and organic photovoltaics. One emerging application involves organic thermoelectrics (OTEs), which interconverts heat and electricity. Functionally graded materials (FGMs) provides a pathway to improve performance of thermoelectric devices by locally tuning the material properties across operational temperature gradient. However, FGMs have not been investigated in the field of organic materials. The solution processability of semiconducting polymers provides the opportunity to test different functionally graded models. Here, we report on a double-segmented polythiophene-based conjugated polymer thin film (~30nm) through compositional control of molecular dopant F4TCNQ. By introducing the dopant from the vapor phase, we managed to spatially control TE properties of our segmented film. Macroscopic in-plane charge transport properties were measured within and across segments. The effective Seebeck coefficient matches known models. This preliminary study on functionally graded organic thermoelectric materials provides guidelines to further development on more complex FGMs. |
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L70.00006: Mechanism of charge transfer in polymer/fullerene-free type organic solar cell Nozomi Ohta, Azusa Muraoka, Koichi Yamashita Recently, in the research fields on the organic solar cells, it has been reported that it succeeded in synthesizing polymer / fullerene-free (donor/acceptor) type organic solar cell, and showed the light conversion efficiency higher than polymer/fullerene-free type. In this study, focusing on polymer / fullerene-free type PTB7 / ITIC complex, we obtain the electronic structure of complex and absorption spectrum at donor / acceptor interface using time dependent density functional theory method. In addition, from the viewpoint of electronic structure, absorption spectrum, and HOMO–LUMO gap, we consider the mechanism of charge transfer in polymer / fullerene-free type organic solar cell. |
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L70.00007: Excimontec: An Open-Source Software Tool for Kinetic Monte Carlo Simulations of Organic Electronic Devices Michael Heiber Kinetic Monte Carlo (KMC) simulations are a powerful computational tool that have been used in concert with experiments and theory to understand and optimize organic semiconductor devices. However, despite over 30 years of applying KMC simulations to organic semiconductors, no standardized software tools have emerged. Instead, many research groups around the world have maintained private codebases of varying complexity, efficiency, and reliability. As a result, there have been large barriers to entry for new researchers and a lot of repetitious efforts that would be much better off applied to further refining the physical models. Excimontec is a new well-tested, reliable, and accessible open-source software tool for performing KMC simulations of organic electronic devices, and this presentation will highlight some of the main features currently available, including time-of-flight charge transport simulations, excited state dynamics simulations, and internal quantum efficiency simulations. |
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L70.00008: Variable Resolution Coarse-Graining of Ion-Coupled Electron Transport in Electrochemically Active Polymers Brett Savoie Conducting polymers that exhibit reversible mass and ion exchange with aqueous media have potential for sensing applications when implemented in organic electrochemical transistors (OECTs). However, the degree to which ion motion is coupled with electron transport and morphology changes, and the range of polymer chemistries that can exhibit and be optimized for electrochemical response in aqueous media is unknown. To address these challenges we have developed the first variable resolution model of hydrated PEDOT:PSS, the archetypical electrochemically active system, with several simple salts. Using this variable resolution model we are able to characterize both long-timescale morphology reorganizations and the corresponding short-timescale evolution of the conducting polymer electronic structure and develop design rules for optimal doping and hydration levels in PEDOT-based systems. The generality of this approach creates an opportunity to establish to what degree PEDOT:PSS is representative of other OECT polymers and address the lack of materials diversity in OECT applications. |
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L70.00009: Absorption enhancement in evanescently-coupled waveguides Shamir Maldonado-Rivera In this project the main goal is to construct various thin films of different thicknesses of CYTOP and PMMA in a glass substrate using the spin coating. A glass, CYTOP and PMMA was proposed. Although this substrate was bio-imaging oriented in order to enhance resolutions and get better signals when working with bio-samples, is also a good platform for luminescence cooling. In a MatLab simulation, we find that the best thicknesses that will enhance the electrical field on the films surface at a resonant angle between 65-70 degrees are ~600-750 nm and ~350-450 nm, respectively. Then, Glass/CYTOP/PMMA substrate were successfully spin-coated with an optimal thickness achieved between ~700nm (for CYTOP) and ~400nm (for 1wt% of Lumogen Red L305 with PMMA). Photoluminescence (PL) spectra was enhanced and absorption is stronger on thicker films. The reflectivity spectrum shows that the resonant angle was ~47 degrees. The idea of cooling a solid-state optical material by simply shinning a laser beam onto it, the advantages of compactness, the absence of vibrations and moving parts or fluids, high reliability and the ability to operate without cryogens is rapidly becoming a promising technology for future cryocoolers. |
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L70.00010: Optical Super-Resolution Imaging of Block Copolymer Thin Film Surface Morphology Using Fluorescent Silica Nanoparticles Joshua Hinckley, Dana Chapman, Ulrich Wiesner Block copolymers (BCPs) are of tremendous academic and industrial interest, as they exhibit myriad tunable properties useful across a broad range of applications. This is particularly true for BCP thin films. Traditionally, imaging mesostructured BCP surfaces of such films has been dominated by electron and scanning probe microscopies. In recent years, however, high-resolution optical imaging in the far field has provided exciting opportunities for alternative approaches. Here, we report the optical super-resolution imaging of BCP thin film surface mesostructure through stochastic optical reconstruction microscopy (STORM). To that end, we introduce a new class of functionalized silica nanoparticles to enhance the brightness of encapsulated dyes for STORM, offering distinct advantages over conventional sample labeling with organic dyes. These nanoparticles are simply mixed with or attached to specific blocks of the BCPs, thereby enabling selective block staining and optical visualization. This allows for facile imaging of morphological features on the near-molecular scale, thus providing a versatile method for BCP surface morphology assessments using optical imaging. |
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L70.00011: Ion transport properties of block copolymer electrolytes comprising mixed ionic liquids. Jaemin Jeon, Moon Jeong Park Ionic conductivity and mechanical properties of block copolymers comprising various ionic liquids has been extensively studied lately to develop future solid-state polymer electrolytes. It has been found that the independent control of cation and anion in ionic liquid can improve ion transport properties of such materials given that the type of cation and anion determines swelling behavior of ionic domains and interfacial properties of ionophilic/ionophobic phases. In the present study, we investigate ion transport properties of block copolymers comprising different ionic liquids. In particular, by employing mixed ionic liquids, markedly improved ionic conductivity was obtained, far higher than simple sum of known values. The results were understood by dissimilar ion distributions in the substructure of self-assembled morphology, as quantified by combining scattering and spectroscopy techniques. |
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L70.00012: Nanofabrication for Probing Ionic Conductivity Mechanisms in Thin-Film Polymer Electrolytes Veronica Burnett, Paul F Nealey, Shrayesh Patel Ion conducting polymers as solid electrolytes enable the use of high energy density batteries and offer a safe, lightweight, and flexible alternative to traditional liquid electrolytes. However, they suffer from lower room temperature conductivities and Li ion transference numbers than their liquid counterparts as well as poor electrochemical stability. Therefore, it is important to study the ion transport mechanisms within these materials in order to maximize conductivity while retaining these advantageous properties. In this study, we fabricate interdigitated electrode devices with trenches of insulating dielectric SiO2 on the length scale of an insulating block in a block copolymer such as PS-b-PEO. These devices are fabricated so that a percentage of the trenches, which model the conducting pathway of a BCP, are blocked by additional SiO2. A PEO/LiTFSI solution is spincoated and reflowed onto the devices then measured using AC impedance spectroscopy to calculate the conductivity. We report a decrease in conductivity with increasing percent hindered pathways. By eliminating the effects of grain boundaries and interfacial blurring between blocks of a block copolymer, this study elicits a direct relationship between structure and conductivity. |
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L70.00013: Ion Transport in Polymer Blend Electrolytes Bill Wheatle, Venkatraghavan Ganesan In conventional small-molecule battery electrolytes, high ionic conductivity is achieved through blending of high polarity and low viscosity components. One may simply assume that the conductivities of these blended electrolytes will be an average of the intrinsic conductivities of each host, each of which is weighted by its volume fraction. However, it has been shown that the ionic conductivity is instead a nonmonotonic function of the volume fraction of each host, maximizing at some intermediate blend composition. |
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L70.00014: Simultaneous Transient Gel Behavior and Multivalent Ionic Mobility in Polymeric Ionic Liquid-Ligand Gels Seamus Jones, Nicole Michenfelder-Schauser, Glenn Fredrickson, Rachel Segalman Polymeric ionic liquids form labile metal-ligand bonds with cations to delocalize and conduct multivalent metal ions in the solid state. These multifunctional interactions transiently cross-link the polymer network, leading to dramatic enhancements in the storage modulus on some timescales. Correlating the relationship between metal-ligand interaction energies, timescales, and continuum-level mechanical and conductivity properties leads to design rules for multivalent ion-conductive polymers. Oscillatory rheology experiments are used to elucidate metal-ligand coordination timescales while ionic conductivity measurements are used to both understand the timescale of crosslink motion and the mechanism of ion motion in a telechelic poly(methyl acrylate) with imidazole endgroups. |
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L70.00015: Mechanism of pattern formation in polymer ionic liquid blends under the influence of an electric field Vandana Rajput, Anubha Agrawal, Pratyush Dayal Formation of controllable self-assembled patterns in soft materials can be used to design a variety of multifunctional materials with tunable properties. Here, we utilize unique properties offered by the blends of polymers and ionic liquids (PIL) to reveal the mechanism behind the formation of intricate morphological patterns that emerge in these blends in the presence of an external electric field (EF). In particular, we perform stability analyses to identify key parameters that can be used to lock a pattern of a particular wavenumber in PILs. In addition, we reveal that under the effect of an external stimulus, which in our case is the strength of the EF, both ordered and disordered phase morphologies can co-exist. We also show that the increased strength of EF in PIL system results in the formation of alternating layers of polymer-rich and IL-rich phases of different widths. The reason for this behavior is attributed to cation-anion, polymer-anion, and polymer-cation interactions present in the blends. Thus, the effect of EF can drive new patterns and allows the control of these patterns through wavenumber locking. We believe that our approach can be extended to a variety of soft matter blends containing constituents with stark different properties. |
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L70.00016: Polymerized mesophases of triblock copolymer/ionic liquid/monomer for gel electrolytes Alireza Bandegi, Jose L Banuelos, Reza Foudazi Gel polymer electrolyte membranes have many advantages over their liquid counterparts, such as high energy density and flexible geometry. However, one of the major challenges in using the polymer electrolytes is their low ionic conductivity at ambient temperature that limits their practical applications. The development of heterogeneous electrolytes, comprising ion-rich and ion-poor regions, has enabled the decoupling of electrical and mechanical properties. However, ILs possess delocalized charges and are composed of ionic species that are generally large and asymmetric. These characteristics hinder the formation of well-ordered ionic domains and result in low conductivity. The emerging challenge is how to design heterogeneous polymer electrolytes with different shapes of continuous nanochannels to maximize the decoupling of ionic conductivity and mechanical strength. We propose that this challenge can be addressed through the polymerization of mesophases of monomer, ionic liquid, and amphiphilic block copolymers. Our results show that high mechanical strength without sacrificing the ionic conductivity can be obtained by the mesophase templating method. |
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L70.00017: Ionic Conductivity in Telechelic Polyethylenes Oligomers from Fatty Acids Lu Yan, Maneul Häußler, Stefan Mecking, Karen Winey Telechelic polyethylenes (PEs) containing metal cation (e.g. Na+, Cs+ or Zn2+) coordinated carboxylate end groups with 21 or 46 CH2 units (C21 or C46) in between have been synthesized from chain doubling of erucic acid. These linear and monodisperse telechelic PEs crystallize into well-defined lamellar structures with acid or ion-rich layers embedded in the orthorhombic or monoclinic crystallites at room temperature. Interestingly, C46(COOCs)2, C46(COONa)2, and C21(COONa)2 exhibit a crystal phase transition from orthorhombic to hexagonal or monoclinic structure prior to the melt state, according to DSC and X-ray scattering. The crystal phase transition are mainly due to increased chain rotation at elevated temperature, but the strong ionic interaction in the layered structure prevents the crystal from directly melting. The ionic conductivity of C46(COONa)2, C46(COO)2Zn and C46(COOCs)2 exhibit an Arrhenius-like ion conduction behavior suggesting that the ion transport in the layers are decoupled from the PE segmental movements. This work offers important insights for designing telechelic molecules with well-defined morphologies and tunable ion transport properties through the two-dimensional ionic channels. |
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L70.00018: Ion transport and aggregate morphology in precise sulfophenylated polyethylene ionomers Benjamin Paren, Lionel Picard, Patrice Rannou, Manuel Marechal, William Neary, Aaron Kendrick, Justin G Kennemur, Amalie Frischknecht, Karen Winey A set of new and amorphous precise ionomers synthesized by ring-opening polymerization exhibit decoupled ion transport. These precise ionomers consist of a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon, that is fully neutralized by a counterion X (X is Li+, Na+, or Cs+), p5PhSA-X. The morphologies of these ionomers are characterized with X-ray scattering, and the ion transport properties are characterized with electrical impedance spectroscopy. Both experiments are performed under vacuum, from room temperature up to 200°C. Distance between aggregates appears independent of ion type, with an interaggregate spacing of ~1.9 nm present in the Li+, Na+, and Cs+ as-cast ionomers. Atomistic molecular dynamics simulations are used to elucidate the structure of aggregates in the ionomers and compared to absolute X-ray scattering data. The ionomers exhibit conductivity of 10-8 to 10-7 S/cm at 150°C. These materials demonstrate decoupled ion transport up to 200°C, a result of ions traveling within ionic aggregates and independent of chain dynamics. |
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L70.00019: WITHDRAWN ABSTRACT
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L70.00020: Phase behavior of polymerized ionic liquid mixtures in a non-aqueous solvent Minjung Lee, Ryan Hayward The formation of complex coacervates has been a subject of great interest in the field of charged polymers, with a focus almost exclusively on aqueous systems. Herein, we studied the phase behavior of two polymerized ionic liquids, namely poly(1-ethyl-3-methyl imidazolium (3-sulfopropyl) acrylate) and poly(1-(2-acryloyloxy-ethyl)-3-buthyl-imidazolium bis(trifluoromethane) sulfonimide), representing a polyanion and a polycation, respectively, in non-aqueous solutions. By controlling the concentration of the polymers and added salt composed of the two counterions, we studied the conditions for one vs. two phases, which provides useful information for further applications of polymerized ionic liquids, as well as providing an interesting comparison with the phase behavior of other charged polymers such as polypeptides and polysaccharides in aqueous media. |
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L70.00021: Effect of pH on structure of charged nanoparticles in oppositely charged polyelectrolyte solutions Rituparna Samanta, Venkatraghavan Ganesan We study the effect of pH of the solution on the structural characteristics of a system of weakly charged spherical particles in oppositely charged, dissociable polyelectrolyte solutions. The pH dependent dissociation of weak polyelectrolytes is known to affect the adsorption and bridging of polymers on the particles. We have used a hybrid method of single chain in mean field theory and the solution of general Poisson’s equation in a semi-grand canonical framework. We study the effect of charge of particles, volume fraction of particles and polymers, concentration of polymers on the structural characteristics of the suspension. |
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L70.00022: pH DEPENDENT RHEOLOGY OF HYDROPHOBICALLY MODIFIED ALKALI SOLUBLE EMULSION (HASE) POLYMERS Alan Nakatani, Lyndsay Leal, Nikhil Fernandes, Kathleen Michels, Jennifer M Koenig, Catheryn Jackson Two sets of Hydrophobically modified Alkali Soluble Emulsion (HASE) polymers were investigated using steady shear viscosity and dynamic frequency measurements. One set of HASE polymers contained a fixed ratio of ethyl acrylate (EA) to methacrylic acid (MAA) and a hydrophobe (C12, C18, or C22) containing monomer (macromonomer). The second set of HASE polymers contained a fixed amount of MAA but the amount of C18 macromonomer was varied (1%, 5%, or 10% by mass). Aqueous solutions of the polymers (1% by mass) were tested at pH = 3, 5, 7 and 10. The neutralization process is known to impact the solution viscosity, therefore, samples “back-titrated” from pH = 10 to pH = 7 were also tested. The samples at pH = 3 and 5 had the lowest viscosities. Samples directly adjusted to pH 7 had a much higher viscosity and a yield stress, which increased with increasing hydrophobe size. The samples at pH = 10 had the highest viscosity and yield stress values. Samples back-titrated to pH = 7, were lower in viscosity than the samples directly adjusted to pH = 7. The dynamic frequency results at pH = 10 show additional characteristic timescales which shift as a function of the hydrophobe size. |
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L70.00023: Interparticle Interaction between Functionalized Clay Nanosheets Dispersed in Polymer Matrix Supriya Gupta, Paresh Chokshi Incorporation of nanofillers in polymer melt produces composites with extra-ordinary properties due to enhanced surface to volume ratio of the fillers. Fillers are functionalized by grafting polymeric chains on the surface inducing steric stabilizing preventing particle agglomeration. Here, we address the dispersion of clay nanosheets in polymer matrix. We use self-consistent field theory to theoretically construct the polymer mediated interparticle potential curve. The interaction potential is obtained from the inhomogeneous composition field for the polymer segments. First, we examine the interpaticle interaction between two grafted nanosheets immersed in the matrix of polymeric chains of dissimilar chemistry to that of the grafted chains. The interaction potential is repulsive at short separation and shows depletion attraction for moderate separations. Further, we construct the interaction potential between two nanosheets grafted with polymeric chains of varying architectures, like star polymer and diblock copolymer. Nanosheets disperse better in the matrix of star polymer than linear polymer. In surfaces grafted with diblock copolymers, the interplay between the enthalpic and entropic interaction gives rise to a rich behavior in the interparticle interaction potential curve. |
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L70.00024: Novel Properties of Mesostructured Superconductors Synthesized via Block Copolymer Self Assembled Nanocomposites Randal Thedford, Sol Michael Gruner, Ulrich Wiesner The effect of mesoscale confinement or ordering on the properties of superconductors is an active area of study, but to date this work has largely been done using 2D materials. Three-dimensionally mesostructured superconductors are expected to behave very differently than their 2D or bulk analogues, but exploration of such materials has been limited by the lack of available methods for their synthesis. We demonstrate multiple routes to superconductors with mesoscale order and porosity though the self-assembly of block copolymer nanocomposites. This represents a versatile, robust, and tunable platform for the investigation of 3D mesostructured superconductors. Our results show changes in the superconducting properties of multiple materials when synthesized in block copolymer derived 3D periodic structures such as the bicontinuous double gyroid and the alternating gyroid, suggesting quantum metamaterials behavior. |
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L70.00025: In-Situ Monitoring Polymer-graft Functionalization on Gold Nanoparticles and Influences on Assembly Formation Yiwen Qian, Ting Xu Controlled assemblies of polymer grafted nanoparticles can lead to a unique class of material with distinct advantages due to the programmability and diversity endowed from polymer-based-ligands. Surface functionalization of nanoparticles (NPs) with polymer-based ligands plays a critical role in controlling the effective size and ‘interaction softness’. To this end, it is requisite to quantity the attached polymer ligands. Here we present the (in situ) proton nuclear magnetic resonance (1H NMR) study on the ligand exchange of oleylamine by thiol end-functionalized polystyrene as a function of the ligand concentration and particle size on Au NPs. As the extensive overlap of the polymer ligands impede the direct evaluation, we examine the pristine chemical shifts of the oleylamine to characterize the ligand modification. We show that the surface functionalization efficacy depends on the ligand/particle ratio, size of NPs and molecular weight of the polymeric ligands. These quantitative studies enabled us to investigate the influences of the ligand modification and solvent quality on the ordering of the self-assembled polymer grafted nanoparticles with a focus on a polycrystalline assembly to hexagonally ordered superlattice transition. |
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L70.00026: Fabrication of polymer-brush modified Ba-Ti oxide/poly(vinylidene fluoride) nanocomposites thin film Maiko Nishibori, Kohei Nosue, Ayumi Hamada, Yuko Konishi, Atsushi Takahara Polymer composite with high dielectric constant have attracted attention in the micro-electronic industry due to their easy-processing and low cost. In the composite thin film, the surface properties of the ceramics nanoparticle and the volume fraction of polymer to ceramics particles are quite important in order to increase in their functionality. In this study, the surface modification of Ba-Ti oxide nanoparticles (BT) with high-density poly-methyl methacrylate (PMMA) brushes was conducted to improve its dispersibility in poly(vinylidene fluoride) (PVDF) and the fabrication of nanocomposites thin film of PMMA-BT and PVDF was investigated. PMMA brushes on the surface of BT particles were fabricated by Atom Transfer Radical Polymerization with (2-bromo-2-methyl) propionyloxyhexyltriethxysilane as a silane coupling agent. PMMA-BT particles showed high dispersibility in PVDF-DMF and almost no voids and clacks were observed in the composite film of BT-PMMA mixed with PVDF even if the volume fraction of PMMA-BT particles was high to PVDF. The results indicated that the surface modification by polymer-brush could be a promising method to fabricate the composite film having good quality and high dielectric property. |
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L70.00027: Morphological behavior of ABC mikto-arm terpolymer with a C60 Hyeyoung Kim, Matthias ML Arras, Sergey Chernyy, Duk Man Yu, Gregory S Smith, Thomas Russell We observed the morphological behavior of ABC mikto-arm terpolymer with a C60 additive. ABC mikto-arm terpolymers, consisting of polystyrene, polyisoprene and poly(2-vinylpyridine) (PS-PI-P2VP), with various P2VP volume fractions were examined. The role of C60 on the morphological behavior of mikto-arm terpolymer was studied by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The affinity of C60 to PS or P2VP was examined by neutron reflectivity. C60 can form charge-transfer complexes with electron donating pyridine groups in P2VP blocks. Before and after charge-transfer reaction, C60 showed different effects on the self-assembly of mikto-arm polymers. The domain spacing, interfacial width, and morphology of mikto-arm terpolymers were changed depending on the concentration of C60. |
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L70.00028: Desorption of Water Collected on Hygroscopic Polymer Nanofibers Zhihao Shang, D Reneker The high surface area-to-mass ratio make nanofibers an optimal material structure for water absorption from humid ambient air. Water molecules were concentrated on the surface of hygroscopic nanofibers. Strong nanofibers withstood the forces from the flowing air that carried water molecules to within about 100 nm of the fiber surfaces. Nanofiber surfaces became saturated with water molecules. Microwave energy with frequency of 2.45 GHz caused rapid evaporation and formation of a bolus of steam in the air stream. The bolus was collected and the water condensed in an external condenser. Alternatively, high voltage DC was applied to two edges of a thin mat of hygroscopic nanofiber to evaporate water from the nanofiber mat. The apparatus provides a useful method to test water absorption ability of different hygroscopic nanofibers. It also provides other information needed to design large scale water collectors. |
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L70.00029: A Colloidal Model to describe the effects of mixing time on filler dispersion in industrial nanocomposites Vishak Narayanan, Kabir Rishi, Greg Beaucage, Vikram K Kuppa, Alex McGlasson, Michael Chauby The properties of industrial nanocomposites such as tires depend on the degree of filler dispersion under high-shear mixing. Conventionally, the dispersion is quantified through an index based on the reduction in micron-scale agglomerate size observed in micrographs and bulk electrical conductivity measurements. An alternate nano-scale dispersion technique based on x-ray scattering has been proposed.1 The impact of mixing time on dispersion is investigated taking advantage of the van der Waals equation to describe excluded volume and interaction energy in the dispersion. Herein, an analogy is made between thermally driven true colloidal dispersions and total accumulated strain in nanocomposites. The excluded volume depends only on the filler type and seems insensitive to bound rubber whereas the interaction energy is strongly dependent on viscosity and polymer chemistry. Moreover, the wetting time for nano-scale incorporation of elastomer into filler can be predicted. The description of nano-scale dispersion via a pseudo- second virial coefficient offers the additional possibility of determining the interaction potential that can be used for coarse grained simulations. |
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L70.00030: Entropy driven assembly in multicomponent nanocomposite Le Ma, Peter Ercius, Ting Xu Hierarchically structured nanocomposites show unique collective properties from nanoparticle (NP) assemblies. Successfully structure control in nanocomposite remains as bottleneck to advance the field. Block copolymer (BCP) and supramolecular systems have been effective in achieving nanoscopic dispersion of fillers. However, NPs with size larger than 30% of the BCP specific domain size tend to aggregation due to the large conformational entropy penalty. This limitation in the particle size restricts the NP incorporation for targeted functionality. Here, we will discuss a new approach to modulate thermodynamic contribution from various components with a special focus of maximizing translational entropy. The present studies suggested that manipulating entropic contribution in multiple components system will lead to new path and opportunity toward structure control and access functionality. |
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L70.00031: Nafion Nanocomposite Fuel Cell Membranes for Improved High Temperature Performance Donovan Weiblen, Krista Biggs, Alianna Maguire, Deniz Rende, Rahmi Ozisik Proton exchange membranes represent an active area of fuel cell research. Current work seeks a membrane with excellent proton conductivity, minimal permeability of oxygen and fuel, and stable physical properties. At temperatures above 90 °C, traditional Nafion membranes experience decreased proton conduction, decreased water uptake, and softening. Although the performance is still being improved, addition of silica nanoparticles to Nafion membranes is known to improve conduction and water uptake at high temperatures. Recent work shows a new polymer nanocomposite system that stiffens repeatably and reversibly with increasing temperature via interfacial heterogeneous dynamics between a matrix polymer with low glass transition temperature (Tg) and high Tg polymer modifier adsorbed to silica nanoparticles. Studies were completed to investigate the applicability of this phenomena to Nafion using silane coupling agents to achieve improved high temperature performance. The effects of silica nanoparticle and grafted modifier concentration, and grafted chain structure and dynamics on Nafion nanocomposite structure and properties, particularly thermal stiffening, were studied. |
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L70.00032: Growth and Bulk Effects of Irreversibly Adsorbed Layers in Polymer Nanocomposites Katelyn Randazzo, Rodney Priestley Recent studies have demonstrated that the formation of irreversibly adsorbed layers at the polymer-substrate interface can significantly affect the overall properties in thin films. However, little attention has focused on the polymer nanocomposites, where irreversibly adsorbed layer growth is expected to be an important parameter due to the amount of surface area and high temperature processing. In this work, we characterize the growth of irreversibly adsorbed layers of polystyrene atop silica nanoparticles, which we correlate to the resulting bulk properties of polystyrene-silica nanocomposites. Our approach compares bulk properties measured via traditional means such as DSC with a direct measurement of local properties achieved by fluorescence spectroscopy. We expect the characterization of irreversibly adsorbed layers and their bulk effects to be useful in engineering new polymer nanocomposite materials. |
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L70.00033: Biomimetic Nanocoatings with Exceptional Mechanical, Barrier, and Flame Retardant Properties from Large Scale One-Step Co-assembly Fuchuan Ding, Jingjing Liu, Luyi Sun Large-scale biomimetic organic/inorganic hybrid nanocoatings with a nacre-like microstructure were prepared via a facile co-assembly process. Different from conventional polymer nanocomposites, such nanocoatings contain a high concentration of nanosheets, which can be well aligned along the substrate surface. Moreover, the nanosheets and polymer matrix can be chemically co-crosslinked. As a result, the nanocoatings exhibit exceptional mechanical properties (high stiffness and strength), barrier properties (to both oxygen and water vapor), and flame retardancy, but meanwhile they are highly transparent (maintaining more than 85% of their original transmittance to visible light). The nanocoatings can be applied to various substrates and regular or irregular surfaces (e.g., films as well as foams). Because of their excellent performance and high versatility, such nanocoatings are expected to find widespread application. |
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L70.00034: One Component Silver-Polystyrene Nanocomposites: The Interplay of Thermoplasmonics and Elastic Mechanical Properties David Saleta Reig, Patrick Hummel, Zuyuan Wang, Sabine Rosenfeldt, Bart Graczykowski, Markus Retsch, George Fytas
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L70.00035: Coassembly of binary nanoparticle systems Jiuling Wang, Brian Lee, Gaurav Arya The spatial distribution of nanoparticles (NPs) in polymer nanocomposites plays a critical role in governing their mechanical and optical properties. Although there have been many studies focusing on the assembly of uniform-sized NPs in polymers, relatively few studies have investigated the coassembly of NPs of different sizes and surface properties. Using a lattice Monte Carlo approach, we investigated the morphology of heterogeneous NP structures assembled from NPs of different sizes and surface properties. Our results indicate that these particles assemble into networks with different pore sizes, fractal dimensions and local aggregation interfaces depending on the particle sizes and sticking probabilities between them. The effects of the initial distribution of NPs on the assembly will also be discussed. Our findings provide guidance for controlling NP assembly and could help us design nanocomposites with superior mechanical and optical properties. |
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L70.00036: Hybrid computer simulations of block copolymer/nanoparticle systems Marco Pinna, Javier Diaz, Ignacio Pagonabarraga, Andrei Zvelindovsky Polymer nanocomposites have been shown to display improved properties over their purely polymeric counterparts. Furthermore, block copolymers (BCP) are perfect candidates to control the localisation of nanoparticles. Nonetheless, the presence of nanoparticles can distort the BCP properties such as morphology and thus colloids act as more than just passive fillers. |
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L70.00037: Influence of PVAc/PMMA/Silica Nanocomposite Structure on Properties Chen Gong, Deniz Rende, Rahmi Ozisik Rheological properties of poly(vinyl acetate), PVAc, and silica composites were previously studied as a function of silica concentration and silica surface chemistry. In the current work, we investigate the effect of poly(methyl methacrylate), PMMA, coated silica nanoparticles on the properties of PVAc. PVAc and PMMA are known to form a miscible blend, however, the addition of silica nanoparticles, which forms hydrogen bonds with PVAc might alter the blend morphology and therefore, the blend properties. In addition, by selectively adsorbing PMMA onto silica nanoparticles first, and then embedding them into PVAc might lead to a phase separated interface at the nanoparticle surface. The morphology and rheological properties of PVAc/PMMA/silica nanocomposites were investigated as a function of compositionand silica nanoparticle surface chemistry. |
(Author Not Attending)
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L70.00038: “Energy dissipation of elastomer nanocomposites at large strains and high strain-rates.” Keith Dusoe, Alfred Crosby Characterization of the mechanical behavior of rubbery materials at high strain rates is a nontrivial challenge. Many of the physical properties of rubbers are strain-rate dependent and therefore necessitates the understanding of the high-strain rate response of rubbery materials. Current methods to characterize the mechanical properties of rubbers typical probe the material response under low strain-rate, quasi-static conditions or dynamic conditions at low strain. A highly strained rubber undergoes free retraction when the material is suddenly released from one end. The resulting speed of the retracting material can be very fast, approaching the speed of sound in the material, and is related to the material’s molecular structure, modulus and internal friction. In this work, large strain, high strain-rate mechanical response of elastomer and elastomer-matrix nanocomposite materials are investigated by free retraction of highly-stretched samples. High-speed videos of rubber retraction are acquired and analyzed to characterize the mechanical properties of these materials at high strain rate, large strains. Furthermore, the role of filler-matrix interactions in elastomer nanocomposites in minimizing viscoelastic energy losses at large strain and high strain-rates are considered |
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L70.00039: Nanoparticle Diffusion in Athermal And Attractive Entangled Polymer Melts Eric Bailey, Russell John Composto, Karen Winey Understanding the mechanisms by which nanoparticles (NPs) diffuse in a polymer melt remains an experimental challenge. In this study, we combine Rutherford backscattering spectrometry (RBS) and X-ray photon correlation spectroscopy (XPCS) to probe the diffusion of (i) enthalpically attractive silica (SiO2) NPs in poly(2-vinyl pyridine) melts and (ii) athermal phenyl-capped SiO2 NPs in polystyrene melts. In both systems, RBS shows NP diffusion in reasonable agreement with recent theoretical predictions where the athermal NPs diffuse faster than the attractive NPs. XPCS show quantitative agreement with RBS in weakly entangled polymer melts but in well-entangled polymers, XPCS shows unexpected hyperdiffusive behavior that is not observed in RBS. Our direct comparison of these techniques probes NP diffusion between ~30 and 800 nm, isolates the effect of NP-polymer interaction, and highlights the different sensitivities and observations of these experimental methods. |
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L70.00040: The Study of Mechanical Property of Block Copolymer Composites Tuned by Nanoscale Polymeric Morphology and Nanoparticles Junpyo Kwon, Robert Oliver Ritchie, Ting Xu The Understanding of structure-property relationships in block copolymer nanocomposites is one of the main challenges. Especially, the study of mechanical properties tuned by compositional and structural variables is significant to the applications of the nanocomposites. Here, we focus on the fundamental analysis with regard to the mechanical properties changed by the block copolymer morphologies, the volume fractions of nanoparticles and the strength of interactions between the polymeric matrix and fillers. In addition, we studied thermal annealing effects on the nanoscale structural rearrangements which link to the mechanical behavior changes. |
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L70.00041: Elucidating Synthetic Pathways in the Synthesis of Block Copolymer Self-Assembly Derived Mesostructured Nitrides with in situ Multimodal Synchrotron Characterization Peter Beaucage, Francis J Di Salvo, Sol Michael Gruner, Ulrich Wiesner Block copolymer-inorganic hybrid co-assembly has recently emerged as a scalable, tunable route to crystallographically ordered, mesoporous, highly crystalline inorganics relevant to catalysis, energy conversion and storage, and other areas. The successful synthesis of these materials, however, often relies on heavily tuned thermal processing in order to crystallize a functional inorganic material without crystal growth-induced mesostructure collapse. For example, in our recent efforts to produce gyroidal niobium nitride (NbN) superconductors, a two-step thermal treatment process was needed with temperature sensitivity ca. ± 1%. To enable the rapid discovery and optimization of these synthesis routes, we developed an in situapparatus capable of measuring small- and wide- angle x-ray scattering (SAXS/WAXS) during annealing at temperatures up to 1200 C in reactive gases. In a first application, we have explored the transformation pathways from block copolymer-oxide nanocomposite to nitride, resulting in the first synthesis of a mesostructured nitride from a Pluronics ABA block copolymer. We expect that this system will enable the rapid screening of a variety of block copolymer-derived oxide, nitride, and carbide materials with applications in catalysis, energy, and beyond. |
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L70.00042: Probing the Morphology of Hydrocarbon-Based Anion-Exchange Membranes via Scattering and Computational Methods Eric Schibli, Barbara J Frisken, Steven Holdcroft While perfluorinated polymers dominate the commercial fuel cell industry, hostility to catalysts, difficult and expensive synthetic routes, and challenging disposal hamper wide adoption of fuel cell technology and impede further development. Hydrocarbon-based membranes utilize simple, well-developed synthetic routes that allow for rapid material development. We have investigated a promising series of methylated (benz)imidazole-based ionenes utilizing a combination of lab-scale X-ray scattering and molecular dynamics simulations, based on the united-atom DREIDING model with targeted optimizations to quickly elucidate the morphology of these materials. Derived structure-property relationships may motivate further material development. |
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L70.00043: Investigation of microdomain deformation of thermoplastic elastomer based on in situ synchrotron radiation X-ray scattering Nattanee Dechnarong, Kazutaka Kamitani, Chao-Hung Cheng, Shiori Masuda, Shuhei Nozaki, Chigusa Nagano, Nobuhisa Takayama, Ken Kojio, Atsushi Takahara Microphase separation occurs in polystyrene (PS)-b-poly(ethylene-co-butylene)-b-PS (SEBS), leading PS domains to serve as physical crosslinking points. To investigate behaviors of PS domains, well-ordered SEBS films with low PS content were measured during uniaxial, biaxial and compression testing using in situ SAXS in SPring-8, Japan. After annealing, characteristics of spherical microdomain of PS packed in body-centered cubic lattice were observed in structure and form factors. During uniaxial testing, a shift of structure factor reveals an increase in domain spacing in parallel to stretching direction (SD) while it decreased in the perpendicular to SD. Furthermore, the shift of form factor implies to the deformation of PS spherical domains to egg-like ellipsoidal shape. For biaxial testing, a shift of structure factor indicates an increase in domain spacing as strain increased. In compression testing, the experiment was observed from the edge of sample. It was found that structure factor indicates a decrease in domain spacing in the parallel to compressing direction (CD) while it increased in the perpendicular to CD. The results of form factor observed in biaxial and compression testing suggest the deformation of PS domain, which the sphere became asymmetry in three dimension. |
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L70.00044: Quantification of Nanocomposite Dispersion for Weakly Correlated Systems Alex McGlasson, Greg Beaucage, Michael Chauby, Kabir Rishi, Vikram K Kuppa Nanocomposites such as carbon black dispersions in elastomers can be describe by a mean-field approach and the RPA equation. [1,2] However, dispersion of nanoparticles influenced by surface potentials or entropic and steric interactions, such as for surface-grafted nanoparticles, often cannot be described using the mean-field approach since the particles are weakly organized. For these cases it is necessary to consider a discrete correlation function and an associated structure factor in scattering. Recently Oberdisse and Genix [3] have developed an approach to model scattering from nanocomposites of precipitated silica in elastomers. In this talk an approach similar to Oberdisse is used but with a simpler structure factor based on the Born-Green approach of Guinier and Fournet. [4] The result is a simple parameterization of correlations that can be used to determine the second virial coefficient for direct comparison with uncorrelated systems such as fumed silica or carbon black in elastomers. |
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L70.00045: Electrospun fiber deposition using the gap method alters fiber moduli Christine Helms, Mimi Tran, Garrett Lang, nicole bialick Applications of electrospun nanofibers often require precise mechanical properties and fiber deposition. One common way to control fiber deposition is to use parallel collectors separated by a gap (gap method). In this work, we investigate the effect of gap method deposition on fiber modulus. |
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L70.00046: Evolution of CTAB/NaSal Micelles: Structural Analysis by SANS Christopher Lam, Wei-Ren Chen, Changwoo Do Surfactants self-assemble into micelles in aqueous solution and exhibit structural polymorphism. Under certain conditions, long and flexible structures referred to as wormlike micelles (WLMs) can develop and entangle to form a transient network, leading to spectacular viscoelastic properties. The salt concentration–in particular, the molar ratio of salt (Cs) to surfactant (Cd), Cs/Cd–has been shown to have a significant influence on the viscoelastic properties of WLMs. Salicylate (Sal-) has a strong affinity for the cationic surfactant cetyltrimethylammonium bromide (CTAB) and can promote the growth of WLMs even at very dilute surfactant concentration. We investigate the structure of CTAB/NaSal micelles at relatively low concentration over a wide range of Cs/Cd. Using small-angle neutron scattering and the most advanced scattering function for WLMs, we characterize the development and structural evolution of wormlike micelles both qualitatively and quantitatively, culminating in an understanding of the phase behavior of CTAB/NaSal within this region of phase space. |
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L70.00047: Thermodynamic stability of worm-like micelle solutions and the corresponding ion behavior Karsten Vogtt, Hanqiu Jiang, Greg Beaucage Worm-like micelles are nano-scale self-assemblies widely used for viscosity enhancement, for drug delivery, and in personal care products. The stability of WLMs under variable ionic and surfactant concentrations is important to applications of these fascinating materials. A mixed surfactant system consisting of sodium laureth sulfate and cocoamidopropyl betaine was examined using small-angle neutron scattering. It is demonstrated that structural screening, and the associated virial coefficient, has an increasing impact on scattering with increasing surfactant concentration. A linear relationship between the second virial coefficient, A2, and the salt to surfactant ratio, Θs–s, is derived based on SANS results. The Θs–s-dependency is described via association/dissociation kinetics of salt ions between the bulk and an ion cloud surrounding the WLMs. An ion-cloud model for the high ionic strength condition is proposed and verified based on this work. It is also demonstrated that a virial approach can be used to understand and predict WLM stability. |
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L70.00048: Classes of radial wrinkle patterns in capillary wrinkling Jooyoung Chang, Narayanan Menon, Thomas Russell We investigated capillary force induced wrinkling of polymer (PS, PMMA, and Cytop™ (poly(perfluoro(1-butenyl vinyl ether)) films, floating on an air-water interface. As previously studied, this wrinkle pattern is generated by the capillary force exerted by a water droplet placed at the center of the floating film. When a large range of film thickness is used (10 nm to 1 μm) we observe a qualitative change in the wrinkle pattern in three different thickness regimes: In the thickest films (600 nm ~ 1 μm) a single wave number is seen throughout the bulk of the pattern. In intermediate thickness films (50 nm ~ 600 nm), the bulk wave mode cascades into higher wavenumber close to the contact line. In the thinnest films (10 nm ~ 50 nm) the high wavenumber mode is decorated with a lower frequency component. We will discuss possible mechanistic causes for these distinct patterns. |
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L70.00049: Influence of Side Chain Isomerism on the Conformation of Poly(3-alkylthiophenes) in Solutions Revealed by Neutron Scattering Kunlun Hong, Yangyang Wang, Changwoo Do, Christopher Lam, Wei-Ren Chen Using small angle neutron scattering, we conducted a detailed structural study of poly(3-alkylthiophenes) dispersed in deuterated dicholorbenzene. The focus was placed on addressing the influence of spatial arrangement of constituent atoms of side chain on backbone conformation. We demonstrate that by impeding the π - π interactions, the branch point in side chain promotes torsional motion between backbone units and results in greater chain flexibility. Our findings highlight the key role of topological isomerism in determining the molecular rigidity and are relevant to the current debate about the condition necessary for optimizing the electronic properties of conducting polymers via side chain engineering. |
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L70.00050: Relaxation behavior of biodegradable aliphatic-aromatic block copolymers as revealed by dielectric spectroscopy I. Irska, A. Linares, A. Nogales, E. Piesowicz, S. Paszkiewicz, Z. Roslaniec, Tiberio Ezquerra Thermoplastic elastomers are copolymers composed of a hard block, typically a polyester, and a soft block, typically a polyether. Most commercially available poly(ether-ester) thermoplastic elastomers are produced based on petrochemical monomers. The increasing necessity of eco-friendly polymers has driven the interest for the production of thermoplastic elastomers fully or partially based on monomers from renewable sources. Poly(lactic acid) (PLA) is a biodegradable aliphatic polymer which can be obtained from natural products.Here we present dielectric relaxation results of a series of thermoplastic elastomers based on poly(tetramethylene oxide), as soft segment, and on a a multiblock of poly(buthylene terephthalate) (PBT) and poly(lactic acid) (PLA) as hard segment. The results indicate the existence of a single alpha relaxation, associated to the segmental motions above the glass transition temperature, regardless of the PBT/PLA ratio of the hard segment pointing towards an absence of phase segregation between the two blocks within the hard segment. In addition, different local dynamic processes are revealed below the glass transition temperature contributing to a multimodal beta relaxation that can be assigned to different bonds of both hard and soft blocks. |
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L70.00051: Polymer Dynamics in Poly(styrene-isoprene-2,vinylpyridine) miktoarm terpolymers Thomas Kinsey, Emmanuel Mapesa, Kunlun Hong, Joshua Sangoro In this study we employ broadband dielectric spectroscopy to probe the motion of several poly(styrene-isoprene-2,vinylpyridine) (PS-PI-P2VP, respectively) miktoarm star terpolymers with constant “PS” and “PI” block molecular weights, and we vary the molecular weight of the “P2VP” block. A strong but significantly faster secondary, dipolar relaxation is observed over wide temperature and frequency ranges for the terpolymers compared to homopolymers. This process is attributed to local dynamics of the “P2VP” heterocyclic segments. Additionally, to probe the end-to-end dipole vector timescales of the Type-A polymer chains in the “PI” block, lithium salts were added to suppress the β-process of the “P2VP” block due to coordination of the nitrogen in the heterocycle with the Li+ cation. These data for the “PI” chain relaxation are compared the dynamics of poly(isoprene) in phase separated linear diblock and homopolymer systems. We show that this unique miktoarm star architecture greatly affects the dynamics in these polymers, and discuss the results in terms of polymer dynamics in well-studied phase separated systems. |
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L70.00052: Low frequency complex dielectric response of dilute clay suspensions Ling Feng, Chang-Yu Hou, Nikita Seleznev, Denise Freed In this work, we measured the low-frequency complex dielectric dispersion of dilute clay suspensions using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. Complex dielectric spectra of smectite and illite suspensions in brine with different weight fractions were obtained. The brine salinities ranged from 100 to 3000 ppm. We fit our results to an effective medium model incorporating the dielectric response of a charged oblate spheroid immersed in an electrolyte. We found reasonable agreement between our measurements and the model; they both exhibited the same trends when the brine salinities and weight fractions of the clays were varied. When the clay grains have a narrow size distribution, we expect that the dispersion of the complex conductivity phase exhibits a near-resonance peak associated with the size of the particles. In our case, because the clay grains have a broad size distribution, the phase peak is broadened. The parameters obtained from the fit agree reasonably well with independently measured quantities, including the size distribution and cation exchange capacity of the clays. |
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L70.00053: Entanglement Effect on Mechanical Properties in Ultra-thin Glassy Polymer Films Cynthia Bukowski, Reed Bay, Alfred Crosby Entanglement density can influence the large strain and failure responses of ultra-thin glassy polymer films. For model films of high molecular weight polystyrene (PS), recent results show severe embrittlement as film thickness decreases below the average size of an unconfined chain. The hypothesized cause for this effect is the loss of interchain entanglements as polymers statistically interact with themselves more than neighbors in dimensionally-confined geometries. Introducing polymer chains shorter than the entanglement molecular weight can also lower the entanglement density, effectively swelling the entanglement network. Here, we blend short (10 kDa) and long (151.5 kDa) PS chains and measure the changes in mechanical properties using the recently developed TUTTUT (The Uniaxial Tensile Tester for Ultra-Thin films). We measure the complete uniaxial stress-strain response of 100 nm PS films as a function of blend concentration. We observe a decrease in yield stress and strain with increasing diluent concentration. Above a critical diluent concentration, the entanglement density reaches a limit where films are too brittle to manipulate. These results establish the framework of how entanglement density affects mechanical properties of ultra-thin polymer films. |
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L70.00054: Effect of Topological Constraints on the Glass Transition Behaviors of Polyrotaxanes Kazuaki Kato, Akihiro Ohara, Hideaki Yokoyama, Kohzo Ito We report here peculiar glass transition behaviors attributed to the topological interactions between two different components of a mechanically interlocked polymer. A new class of polymer glasses were recently materialized from polyrotaxanes, which are necklace-like supramolecules composed of a linear polymer and threaded cyclic molecules. Some of the glasses were ductile and extensible to more than four-folds in length because of the slipping of threading chains through the rings in the region where the stress is concentrated. The unique structural change forced by large deformation seems to relate to the molecular dynamics. In the glass transition regime, the relaxation mode is almost an Arrhenius dependence on temperature, suggesting negligible cooperativity of molecular motions. In addition, a new viscoelastic relaxation at slightly slower than the glass transition regime is generated, when the number of rings in a single threaded chain (so-called “coverage”) is increased. The slower relaxation is significantly prolonged by the increase in coverage. It suggests that the increased topological constraints between different components restrict the translational motions of the rings dragging the threading chain. |
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L70.00055: Alternation of thin film morphology with monomer modifications Qiming He, Dean Mastropietro, Wei Chen, Matthew Tirrell The morphologies of a group of well-defined fluorine-containing copolymers, poly(methyl methacrylate)-b-poly(perfluoroalkyl methacrylate) (PMMA-b-PFMA) with chemical compositions on silicon substrates have been investigated. Thin polymer coatings were prepared on silicon substrates by spin coating from polymer solutions of varying composition and suspended in varying solvents and characterized using atomic force microscopy (AFM) tapping mode height and phase traces. By varying the chemical compositions slightly in the copolymers, alternation of morphologies can be achieved, which provides a unique way to engineer the polymeric coatings on substrates with varying mechanical and surface properties. |
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L70.00056: Self-assembled Copolymer Adsorption Layer-Induced Block Copolymer Nanostructures in Thin Films Dong Hyup Kim, So Youn Y Kim Generally, a very thin adsorption layer originated from the irreversible chain adsorption on solid substrates exists in polymer thin films, which often governs the macroscopic property of the polymer films. Thus, even in microphase separated block copolymer (BCP) films, an adsorption layer can be present playing a critical role in BCP self-assembly. However, understanding on the adsorption layer in BCP films has not yet been elaborated, and therefore its effective control has not been discussed. Herein, we employ self-assembled copolymer adsorption layers (SCALs), transferred from the self-assembly of BCPs at the air/water interface, as an effective way to control adsorption layers in BCP thin films. SCALs are irreversibly adsorbed onto substrates and can replace the natural adsorption layer when other BCP is additionally coated. We further show that SCALs can guide the film nanostructures as it provides topological restrictions and enthalpic/entropic preferences for additionally coated BCP self-assembly. Thus various novel nanostructures of SCAL-induced self-assembly are introduced such as arrays of spacing-controlled hole/dot pattern, dotted-line pattern, dash-line pattern, anisotropic cluster pattern, and etc. |
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L70.00057: Morphological Evolution of Poly(solketal methacrylate)-block-polystyrene in Thin Films Duk Man Yu, Darren Smith, Hyeyoung Kim, Jose Kenneth D. Mapas, Javid Rzayev, Thomas Russell The morphological evolution of the lamellar microdomains for the thin films of symmetric poly(solketal methacrylate-b-styrene) (PSM-b-PS) copolymers that can be converted into poly(glycerol mono-methacrylate-b-styrene) (PGM-b-PS) copolymers by the hydrolysis reaction was investigated. This simple hydrolysis was performed in the solid state using an acid vapor and markedly improves the segmental interaction parameter (χ) from 0.035 to 0.438 at 25 °C. For the perpendicular orientation of the lamellar microdomains, the hydroxyl-terminated random copolymer (PSM-r-PS) with fPSM = 0.5 was used to tune the interfacial interactions at the substrate as a neutral and it can also be transformed into PGM-r-PS with the block copolymers. Scanning force microscope (SFM) and grazing-incidence small angle X-ray scattering (GISAXS) measurements as a function of the exposure time to an acid vapor were conducted to characterize the transition from the disorder to order state as well as the perpendicular orientation and features of the lamellar microdomains. As a result, sub-10 nm full pitch lamellar patterns in the thin films were achieved after full conversion and thermal annealing. |
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L70.00058: Highly Ordered, Complex Morphologies in Block Copolymer Films Obtained by Spatial Confinement Using Topographical Substrates Elisheva Michman, Roland Stenger, Marcel Langenberg, Marcus Mueller, Roy Shenhar Block copolymers microphase separate into periodic arrays of nanostructures. Thin films of these self-assembled BCPs are finding increasing use as platforms for nanofabrication, either as lithography masks or as templates for the patterning of nanowires and particles. Directed self-assembly, using a chemical or topographical pre-pattern, increases the long range order of BCP thin films and can be used to introduce diversity to the BCP morphology. However, the ability to pattern BCPs in a variety of morphologies in close confinement usually requires multiple fabrication steps and is limited in scope. |
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L70.00059: Quasi-Two-Dimensional Assembly of Bottlebrush Block Copolymers with Nanoparticles in Ultrathin Films: Combined Effect of Graft Asymmetry and Nanoparticle Size Yaron Aviv, Esra Altay esraalta@buffalo.edu, Lea Fink, Uri Raviv, Javid Rzayev, Roy Shenhar Block copolymer guided assembly of nanoparticles leads to the formation of nanocomposites with periodic arrangement of nanoparticles, which are important for applications, such as photonic devices and sensors. However, linear block copolymers offer limited control over the internal arrangement of nanoparticles inside their hosting domains. In contrast, bottlebrush block copolymers possess unique architectural attributes that enable additional ways to control the local organization of nanoparticles. In this work, we studied the co-assembly of 8 and 13 nm gold nanoparticles with three bottlebrush block copolymers differing in the asymmetry of their graft lengths in ultra-confined films, where assembly occurs quasi-two-dimensionally. Our results indicate that graft asymmetry could be used as an additional tool to enhance nanoparticle ordering by forcing them to localize at the center of the domain regardless of their size. This behavior is analyzed in terms of the influence of the graft asymmetry on the average conformations of the blocks. |
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L70.00060: Kinetic Pathway Dependent Supramolecular Nanocomposite Assembly on Patterned Substrates Katherine Evans, Ting Xu Block copolymer (BCP)-based supramolecular nanocomposites are promising materials to create hierarchically structured materials and incorporate and organize nanoparticles (NPs). Assembling these materials on lithographically patterned substrates combines the advantages of “bottom-up” and “top-down” assembly to yield materials where the exact ordering and placement of NPs can be controlled. However, for traditional BCP self-assembly on patterned substrates, the width of the underlying pattern must be commensurate with the periodicity of the BCP due to thermodynamic constraints. Here, supramolecular nanocomposites are assembled onto several different geometrically patterned substrates, including lines and concentric circles. On these patterns, incommensurability between the pattern and the supramolecule periodicity was not observed. Instead, the supramolecule self-adjusts to a smaller, non-equilibrium periodicity in the trench. This phenomenon is attributed to the kinetic pathway taken during assembly. |
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L70.00061: Protein-Polymer Block Copolymer Thin Films for Detection of Small Proteins in Biological Matrices via Size-Exclusion Justin Paloni, Bradley David Olsen While biosensors have been developed to allow sensitive detection of biomolecules, limit of detection (LOD) is often increased by several orders of magnitude in biological matrices due to nonspecific binding events from off-target molecules. Here, we demonstrate the self-assembly of protein-polymer conjugate thin films into lamellar structures containing alternating domains of proteins and polymer meshes that can exclude molecules based on particle size. By comparing the diffusion of two analytes, streptavidin (52.8 kDa) and monomeric streptavidin (15.6 kDa), it is found that the larger protein streptavidin experiences greater resistance to diffusion into the films and is largely excluded from the film structure. Furthermore, by decreasing the polymer molecular weight and therefore the spacing of the polymer nanodomains, the thin films can be tuned to enhance selectivity for smaller molecules. When compared against a traditional surface-immobilized protein biosensor, the conjugate films achieve a two order of magnitude reduction in LOD when detecting monomeric streptavidin, resulting from both the greater density of binding sites within the thin films as well as the size-based exclusion of larger proteins. |
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L70.00062: Interfacial Interaction Effects on Phase Transition Behavior of Block Copolymer Thin Films Yeongsik Kim, Daeseong Yong, Hyungju ahn, Jaeup Kim, Du Yeol Ryu Confined in a film geometry, the preferential interaction of the polymer/air and polymer/substrate interfaces generates cylindrical and lamellar microdomains oriented parallel to the substrate. We presented the thickness dependent phase diagram of BCP films using ex-situ grazing incidence small-angle x-ray scattering (GISAXS) and transmission electron microscopy (TEM). With decreasing film thickness (t) when t < to, where to is an onset thickness above which the ODT temperatures (TODTs) of the films are independent of film thickness, the TODTs of cylinder- and lamella-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films supported on preferential substrates remarkably increase. Consistent between cylinder- and lamella-forming PS-b-P2VP films, this effect is so intense in very thin BCP films. |
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L70.00063: Top Coats: Control of Orientation, Alignment and Morphologies of Sub-10 nm Block Copolymer Microdomains Eunjin Kim, Eunkyoung Yoon, In Hyu Ryu, Jinwoo Oh, Jeong Gon Son Achieving sub-10 nm high-aspect-ratio patterns from diblock copolymer self-assembly requires both a high interaction parameter (χ, determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high-χ copolymer typically have very different surface energies, favoring in-plane microdomain orientations. We introduce top coat for the control of orientation, alignment and morphology of a high-χ block copolymer, poly(styrene-block-dimethylsiloxane) (PS-b-PDMS). Using partially hydrolyzed PVA top coats with a solvent annealing, perpendicular orientation of PS-b-PDMS can be obtained despite the large surface energy differences between PS and PDMS. Extremely straight and laterally aligned cylindrical microdomain of BCP films were prepared by simply covering the BCP films with a top coat and dewetting the latter via thermal annealing to generate shear flow in the BCP underlayer. We also observed the gyriod-cylinder phase transition using interfacial-energy-tailored top-coat. At the optimized top-coat composition, gyroid nanostructures with sub-10 nm strut width were achieved down to ∼125 nm. |
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L70.00064: Thin Films of Block Copolymer-Based Supramolecules with Feature Size Over 50 nm Katherine Evans, Emma Vargo, Ting Xu Block copolymer-based supramolecular self-assembly offers a simple method to |
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L70.00065: A facile route to calculate the effective volume fractions in block copolymers during solvent vapor annealing Saeed Behzadinasab, Julie Albert The nano-scale domains obtained from self-assembly of block copolymers (BCPs) have attracted significant attention. In a BCP system, solvents are oftentimes used to plasticize the polymer molecules and reduce the unfavorable interactions in between to facilitate the microphase separation. However, it is not straight-forward to predict the final morphology of a BCP system due to the critical impacts of the annealing condition on the nanostructure. The effective volume fraction of each block remains constant when a neutral solvent is used, while selective solvents can significantly change this parameter and encourage the formation of a distinct morphology. To monitor morphology changes, advanced in-situ techniques, such as X-ray or neutron scattering, which are not readily accessible, are required. In this work, we present a facile route to predict the morphology of BCPs during solvent vapor annealing by simultaneous calculation of the Flory-Huggins theory coupled with mass conservation. This results in the prediction of effective volume fractions of each block, which can significantly reduce the number of required experiments in morphological studies. |
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L70.00066: Influence of salt additives on unconfined melt electrospinning of thermoplastics Neelam Sheoran, Brenton Boland, Elnaz Shabani, Russell E Gorga, Jason Bochinski, Laura Clarke Incorporation of ionic or salt additives into thermoplastic melts can effect both viscoelastic properties and ionic conductivity. Such an approach might usefully alter the process of melt electrospinning where jet diameter (and subsequent fiber size) is influenced by melt viscosity as well as ionic motion within the melt under the influence of a strong applied electric field. These changes have the potential of producing mesoscale thermoplastic nanofibers which are important for filtration and biological applications where high strength nanofibrous materials are required. We report ionic conductivity measurements obtained using broad-band impedance spectroscopy of commercial linear low-density polyethylene (ASPUN 6850A) as a function of temperature, salt type, and concentration, along with corresponding information on viscosity changes. The salt-doped melts were electrospun in an unconfined geometry; changes in jet formation time, number of jets, jet and cone widths, and the resulting fiber diameters were determined. We discuss results and current understanding of the changes in melt properties due to salt additives. |
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L70.00067: Reactive Processing of 3D Printed ABS Structures Formed by Fused Deposition Modeling to Reduce Structural Anisotropy Kaizhong Guan, Mark Dadmun Fused deposition modeling (FDM) is one of the most common additive manufacturing methods, which allows the fabrication of complex structures and customization. However, due to its layer-by-layer nature, the resultant structures exhibit anisotropic properties. A primary reason for the anisotropy is weak interactions and poor entanglement between subsequently deposited layers. Methods to increase inter-layer adhesion include post-deposition heating, which results in loss of fidelity of the fabricated shape to the target structure. To address this shortcoming, our group has modified an FDM printer to allow for the reactive processing of the interlayer interface as a part of the deposition. This is realized by adding a UV-LED optical fiber to an FDM 3D printer, which is designed to initiate a reaction at the inter-layer interface. This presentation will present results that examine the success of this novel processing scheme. Samples of ABS that include a photo-initiator and a crosslinker to form covalent bonds across the interlayer interface are printed with this modified printer, and its tensile properties and anisotropy monitored. This presentation will report the impact of the loading of photo-initiator and crosslinker on the mechanical properties of the printed sample. |
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L70.00068: Droplet-Jet Shape Parameters Predict Electrospun Polymer Nanofiber Diameter Suqi Liu, D Reneker The relationships between observable features of the droplet-jet shape and the diameter of electrospun nanofiber were studied. Three shape parameters were derived from optical images of the jet emerging from a droplet. They are: Left-Right (L-R) curvature, initial jet diameter, and transition slope. Fiber diameter increased as each shape parameter increased. The relation between initial jet diameter and fiber diameter, as well as the relation between transition slope and fiber diameter, were not affected by the variation of voltage or viscosity of the polymer solution. Ambient temperature and humidity were controlled. Day-to-day variations in other ambient conditions that might have occurred in the laboratory do not invalidate these relationships. |
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L70.00069: WITHDRAWN ABSTRACT
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L70.00070: Solvent Effects on the Crystallization Order and Morphology in PEO-b-PCL Copolymers Ryan Van Horn, Cole Tower, Natasha Brigham, Kristi M Allen, Allison Carandang Physical structure of block copolymer films plays an important role in the macroscopic properties of the material. Where applicable, crystallization is one important aspect of the physical structure. PEO-b-PCL copolymer films have two crystalline components that makes for rich hierarchical assembly. Using various solvents for film casting has allowed for the opportunity to control this hierarchical assembly. Films were made using various molecular weight samples at varying drying temperatures in an attempt to manipulate the crystallization process. The crystallization order and morphology was monitored via DSC, FTIR, and optical microscopy. It was determined that the relative solubilities of the two blocks influences the film's final structure. |
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L70.00071: Morphology and crystallization kinetics of poly(ethylene brassylate) Daokun Song, Rufina G Alamo, Irma Flores, Alejandro J Müller Poly (ethylene tridecanedioate), also known as poly(ethylene brassylate) (PEB), is a long-spaced aliphatic polyester obtained from a renewable source. PEB in a range of molar mass between 27,000 and 188,000 Dalton crystallize rapidly as single peaks at ~55 C and display two major melting peaks (60 -70 C). The two melting peaks are associated with crystallites that differ in the packing of the crystalline ester layer. Although the WAXD patterns are undistinguishable, differences in the ester layer packing lead to the effect of self-poisoning at the growth front, and hence to a deep depression of the growth rate at temperatures approaching the transition between both forms, from above. This minimum of the rate, first described for n-alkanes, is also observed in the overall crystallization kinetics obtained by DSC, and follows a general behavior of precision polyethylenes that develop different crystalline polymorphs by changing undercooling. |
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L70.00072: Tunable Liquid Crystallinity of Graphene Oxide by Polymer Crystallization SOHJIN MUN, So Youn Kim Graphene oxide (GO) can form liquid crystals (LC) in aqueous solution, which can be an advantage for many applications using GO. One of the attractive applications is GO based polymer nanocomposites where GO can act as an effective nanofiller in semicrystalline polymer matrix. Previous studies have shown that polymer can be crystallized on GO surface and thus adding GO controls the polymer crystallinity and changes the macroscopic property of GO. However, less attention has been paid to how crystallizable polymers can conversely alter the liquid crystallinity of GO. Herein, we show that GO LC can be correlated with polymer crystallization. We found that the stability and directionality of GO LC can be affected by the rate of polymer crystallization. The microstructure and rheological property of GO LC are extensively investigated with small-angle X-ray scattering and rheometry experiments at a given temperature profile for polymer crystallization. |
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L70.00073: Controlling of Chain-Level Structure of Polymer via Freeze-Drying Toshikazu Miyoshi Freeze-drying (FD) method may potentially control chain-level structures of polymer with varying entanglement densities. In this work, we investigated phase structure, chain-to-chain distance, <R> and self-assembled chain structure of 13C labeled poly(L-Lactic Acid) (PLLA) formed via FD from both good and poor solvents, by solid-state (ss) NMR. It is found that the FD-PLLA from the good solvent adopts an amorphous state while the FD one from the poor solvent forms a semicrystalline state with a crystallinity of ~ 40 %. By comparisons of the 13C-13C Double Quantum (DQ) experimental and simulated curves, it is demonstrated that i) FD-PLLA chains from both poor and good solvents adopt the same <R> value of 6.2 Å. ii) FD-PLLA chains in the latter adopts much larger nanoclusters via folding than those in the former, and is slightly smaller than those in the single crystals. While the FD-PLLA chains obtained from good solvent exhibited similar structure with the bulk glassy state. It is concluded that different solvent-polymer affinities do not affect <R> and significantly affect self-assembly structure of individual chains. |
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L70.00074: Liquids That Freeze When Mixed: Co-Crystallization and Liquid-Liquid Equilibrium in Polyoxacyclobutane-Water Mixtures Joyita Bannerjee, Peter Koronaios, Eric Beckman, Robert Enick, John Keith, Sachin Velankar We show that liquid polyoxacyclobutane –[CH2-CH2-CH2-O]n- when mixed with water at room temperature, precipitates solid co-crystals of the polymer and water. Such co-crystals are formally known as a clathrate hydrate. Hydrate co-crystals can also be formed by simply exposing the liquid polymer to saturated humidity. Outside of metal alloys, this is a rare example of an co-crystal whose melting point exceeds that of the pure species, and the only known example of non-reacting liquids that combine to form a solid co-crystal at room temperature. At high temperatures, the same polymer-water mixtures phase separate into two co-existing liquid phases. This combination of co-crystal hydrate formation and LCST-type liquid-liquid equilibrium (LLE) gives rise to an unusual, possibly unique, type of phase diagram. We examine the effects of polymer molecular weight on the phase behavior and show that at molecular weights exceeding ~2000 g/mol, nearly the entire composition-temperature space is split between regions of solid-liquid equilibrium and liquid-liquid equilibrium. Furthermore, this unusual phase diagram produces distinct crystallization pathways depending on whether the mixture is single-phase or two-phase prior to crystallization |
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L70.00075: Crystallization behavior, morphology and mechanical properties of copolymers of syndiotactic polypropylene with branched monomers Claudio De Rosa, Miriam Scoti, Finizia Auriemma We report a study of the structure and mechanical properties of copolymers of syndiotactic polypropylene (sPP) with different comonomers from ethylene to branched a-olefins. The effect of the presence of short or long branches on the crystallization behaviour and elastomeric properties of sPP has been analyzed. Incorporation of long branched comonomers, as 1-octadecene and 1-eicosene, allows fast decrease of the glass transition temperature and development of interesting elastomeric materials. The relationships between structure and stress-induced phase transformations and mechanical properties have been clarified. In samples with low comonomer content the elastic properties are associated with a reversible polymorphic transition that occurs upon stretching and releasing the tension, which provides an enthalpic contribution to the elasticity. Samples with higher comonomer concentrations show very low crystallinity and a typical thermoplastic elastomeric behavior. The study of the crystal morphology shows the presence of small bundles of rod-like lamellar crystals in all copolymers whose size decreases with increasing content and size of comonomeric units. The small needle-like crystals act as knots of an elastomeric lattice, explaining the development of elastic properties. |
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L70.00076: Fractionated and confined crystallization of polybutene-1 in immiscible polypropylene/polybutene-1 blends Chenguang Liu, Yao Xu, Huarong Nie, Aihua He The crystallization of immiscible polypropylene (PP)/polybutene-1 (PB) blends, in particular the effect of crystal morphology of PP (HTC) on the subsequent crystallization behavior of PB (LTC) was studied. We firstly deemed that PP/PB blends are not complete compatibility but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought different PP crystal morphologies and PB was segregated and confined at different locations. Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature. As temperature continued to fall below Tm of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites reflecting as the decreased crystallization temperature (Tc) of PB and the formation of form I’ beside form II. If PP previously crystallized at high Tc, fractionated crystallization of PB became prominent and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains. |
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L70.00077: Crystallization of trans-1,4-polyisoprene Huarong Nie, Xiao Han, Aihua He, Huicheng Ren Isothermal crystallization of TPI from its solutions and melt were both sudied to attain the kinetic parameters and polymorphic behaivor. The solubility curves of TPI in solvents and the conversion temperatures between isothermal and non-isothermal crystallization were supplied to propose the available concentrations and temperatures for TPI isothermal crystallization. In most cases, the kinetics of TPI crystallization was subject to the Avrami-equation though few deviations arising from the influence |
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L70.00078: Thermodynamic Concepts of the First-Order Prefreezing Oleksandr Dolynchuk, Muhammad Tariq, Thomas Thurn-Albrecht An interaction with a solid surface can induce crystallization in liquids by either heterogeneous nucleation or prefreezing. The latter is seen as the crystalline layer formation at an interface to a solid substrate at temperatures higher than that of a bulk crystal. Most recently, it was ascertained that prefreezing is a first-order transition, since the formation of the crystalline phase is abrupt and reversible. |
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L70.00079: In Situ Electron Microscopy of Polyethylene Glycol Crystallizing in an Ionic Liquid Satyam Srivastava, Alexander Ribbe, Thomas Russell, David Hoagland In this study, the nonvolatile room temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][ETSO]) was chosen as a suitable solvent to study the thermally induced solution crystallization and gelation of polyethylene glycol (PEG) by electron microscopy and electron diffraction. For both phenomena, key features occur at the nanoscale. PEG-IL samples were prepared as thin freestanding or supported liquid films on TEM grids, with crystallization observed upon cooling of heated films to room temperature. In free-standing films, crystals predominantly resided at the liquid surface, and in supported films, on the solid substrate, varied by use of different support films on TEM grids. Crystalline morphologies were observed in the form of rods (width <100nm), fibers, spherulites (80-500 nm diameter), compact faceted single crystals (<100 nm), and interconnected networks. Electron diffraction patterns on the rod- and fiber-like crystals reveal single crystal order at length scales greater than one micron. Electron microscopy and electron diffraction were also performed on fiber-like PEG crystals grown from mixtures of [EMIM][ETSO4] with the less polar ethyltributylphosphonium diethyl phosphate ([P2444] [DEP]). |
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L70.00080: Investigation of Electron Density Mapping of Crystal Structure of Linear Polymers Using Maximum Entropy Method and X-ray Powder Diffraction Data Sono SASAKI, Junki Yamamoto, Miho Nagao, Kenichi Kato, Masaki TAKATA, Shinichi SAKURAI, Kosei Noso (Male, M1 student) The purpose of this study is to visualize the electron density distribution of crystal structure of linear polymers by maximum entropy method (MEM) and X-ray powder profiles measured at SPring-8 (RIKEN, Hyogo, Japan). Crystal structure analysis was carried out for all the reflections by SHELX on WinGX software. Electron density distribution mapping has been investigated for the structure factor (Fobs), phase angle (fcal) and standard deviation (σ) by ENIGMA (Tanaka et al., J. Appl. Cryst., 35, 282-286 (2002)). Tentative results on the MEM analysis for the X-ray powder diffraction data of Polymer crystal will be explained in my poster presentation |
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L70.00081: Gelatinization and Gelation Process of Japanese sweets -Warabi-mochi- Akane Nagasaki, Go Matsuba
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L70.00082: Mesoscale Simulations for Micellization of Diblock Copolymers Chu-yun Huang, Ming-Tsung Lee, Hsiu-Yu Yu Polymeric filomicelles have been considered as drug carriers in nanomedicine for their structural stability and long circulation time in the blood flow. Literature (Geng, Y., et al., Nat. Nanotechnol. 2007) suggests that filomicelles formed by poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-PCL) copolymers have high capacity for paclitaxel (TAX) which could suppress tumor growth. We investigate the micellization of PEO-PCL copolymers using a mesoscale method called dissipative particle dynamics (DPD). Force fields are parameterized to best reproduce the equilibrium configurations of micelles. Inter-species parameters are chosen to reproduce the bulk properties of bead components. The stiffness of the bonds that connect copolymer beads is determined to satisfy the average distance of composing monomers at the same system density. The obtained equilibrium micellar morphologies are simulated in relevant blood flow conditions to characterize the corresponding dynamical response of filomicelles. |
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L70.00083: Anti-biofouling polymer surfaces by a top-down approach Zhixing Huang, Daniel Salatto, Weiyi Li, Leio Koga, Yizhi Meng, Maya Endoh, Tadanori Koga Polymer have been used to develop alternative antifouling coatings against primary protein adsorption. Antifouling polymers have very diverse chemical, structural, and surface topological properties, but they share common physical characteristics: hydrophilic, electrically neutral, or highly hydrated, causing strong interactions with water molecules while reducing interactions with proteins. To stabilize polymer coating under various environmental conditions, chemical end-grafting of polymer chains have been utilized. However, challenges remain in developing a universal non-fouling material that contains the necessary attributes for the next generation of polymer-based anti-biofouling coating technologies. Here we report a radically new paradigm of designing a polymeric coating that is a few nanometers thick (“polymer nanocoating”) with an anti-biofouling property. The nanocoating is composed of homopolymer chains physically adsorbed onto solid surfaces. The results demonstrate that the polymer nanocoatings composed of high surface energy hydrophobic polymers exhibit an antifouling property against a model protein, bovine serum albumin (BSA), while counterpart spin-cast thin films still exhibit adsorption of the protein. |
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L70.00084: Knot untying in elongational fields Beatrice Soh, Alexander Klotz, Patrick Doyle
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L70.00085: Polymer Diffusion Under Cylindrical Confinement James Pressly, Robert Riggleman, Karen Winey Measuring the center of mass diffusion of polymers under confinement is critical for understanding polymer dynamics in applications including semiconductor manufacturing, separation membranes, and polymer nanocomposites. Recent simulations of polymers confined to cylindrical pores reveal non-monotonic changes in the polymer diffusion coefficient, D, as the pore size decreases due to competition between increasing disentanglement and chain segregation. In this study, we use elastic recoil detection to examine the diffusion coefficients of linear polystyrene (Mw = 100-800 kg/mol) confined to cylindrical anodic aluminum oxide (AAO) nanopores (diameter, d = 10-80 nm). The experimental results are compared to the previous coarse grained molecular dynamics simulations to interpret the measured diffusion coefficient in terms of the competition between chain disentanglement and segregation. |
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L70.00086: Theoretical Study of Polymer-Grafted Nanoparticle Translocation Gabriela T Justino, Michael Hore Typically, translocation -- the movement of polymers or particles from one region through a channel into another -- is studied by observing changes in ionic current through the channel as a function of time. As the particle moves through the channel, blockage of the pore results in a decrease in the current. Here, we combine self-consistent field theory (SCFT) and Poisson-Nernst-Planck (PNP) theory to investigate the translocation of both bare and polymer-grafted nanoparticles as a function of the ratio of channel diameter to nanoparticle diameter, polymer grafting density, and electric field strength by computing the expected ionic current traces that would be observed experimentally. |
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L70.00087: Prediction of Stable Morphology of Block Copolymers by using SCF Calculation and Deep Learning Takeshi Aoyagi, Sadato Yamanaka Block copolymers show various microphase separated structure depending on the chain architecture, and miscibility (chi parameter) between different segment type. Various stable phase such as lamellar, double gyroid, hexagonal cylinder and bcc sphere are known, and phase diagram has been studied for simple block copolymers by SCF calculation. However, it is not simple to find equilibrated morphologies even by the calculation, because many metastable morphologies are obtained. Usually, it takes large computational resource to obtain stable structure from many possible metastable structures by real space SCF calculation. |
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L70.00088: Evaluation of Accelerated Aging of Cross-Linked Polyethylene Pipes by Applying Machine Learning Concepts to Infrared Spectra Melanie Hiles, Michael Grossutti, John Dutcher Cross-linked polyethylene (PEX) pipes are emerging as promising replacements for traditional metal or concrete pipes used for water, gas and sewage transport. Infrared (IR) spectroscopy is well suited to the characterization of PEX pipes and additives that are used to achieve long term stability. We have developed a methodology based on IR absorbance peaks to track crystallinity, degree of degradation and the presence of stabilizing additives across the wall thickness of PEX pipes. We observed that, in response to accelerated aging protocols such as heating and UV exposure, the intensities of many IR peaks corresponding to functional groups of both polyethylene and the stabilizing additives are interdependent and highly correlated. We have used principal component analysis to identify and track the IR peaks that are most relevant to pipe degradation. We used these results, together with machine learning techniques such as support vector machines and cluster analysis, to identify and classify different modes of degradation. Our approach highlights the advantages of using machine learning techniques to understand the effects of accelerated aging of PEX pipes, which can be used to refine the pipe manufacturing process to maximize pipe durability. |
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L70.00089: Mobile Doubly Grafted Polymers and their Interaction Min Chu, Dieter Heermann Doubly grafted polymers can, for example, be found in viral membrane proteins. |
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L70.00090: Non-monotonicity in the knotting probability of semiflexible rings: numerical and analytical prediction Erica Uehara, Lucia Coronel, Cristian Micheletti, Tetsuo Deguchi Polymers in canonical equilibrium are prone to become knotted, and the knotting probability for a specific type of knot depends on several conditions, among these we found interesting to study on the effect of bending rigidity of self-avoiding polymers. We use a simple physical mapping to adapt the known asymptotic expressions for the knotting probabilities of self-avoiding polygons to the case of semiflexible rings of beads. We thus obtain analytical expressions that approximate the abundance of the simplest knots as a function of the length and bending rigidity of the rings. We validate the predictions against previously published data from stochastic simulations of rings of beads showing that they reproduce the intriguing non-monotonic dependence of knotting probability on bending rigidity. The mapping thus provides a useful theoretical tool not only for a physically-transparent interpretation of previous results, but especially to predict the rigidity-dependent knotting probabilities for previously unexplored combinations of chain lengths and bending rigidities. In particular, our mapping suggests that for rings longer than 20,000 beads, the rigidity-dependent knotting probability prole switches from unimodal to bimodal. |
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L70.00091: Dynamics of Biodegradation Ryan Sayko, Zilu Wang, Matthew Becker, Andrey Dobrynin Biodegradable polymers are widely used in drug delivery and tissue engineering. However, direct experimental observation of the degradation process of such polymers is limited. To address this issue, we have developed a coarse-grained model to mimic degradation dynamics of L-valine and L-phenylalanine based poly(ester urea)s (PEUs) in vitro. Simulations show that the rates of hydrolysis and chain diffusion control the degradation process. In particular, it is found that PEU’s experience a combination of surface and bulk erosions, which both contribute to the degradation of the material. By tuning the reaction parameters in our simulations, we determine the crossover between degradation-controlled and swelling-controlled regimes. Using these results, we established a general framework for modeling competition between degradation and swelling-controlled mechanisms in biodegradable materials. To test model predictions and to map coarse-grained parameters, we compare the time evolution of the molecular weight distributions of the polymer chains obtained in simulations with those obtained experimentally from size-exclusion chromatography. |
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L70.00092: A Computational Method for Inverse Design Problem in Directed Self-Assembly of Block Copolymers Daniil Bochkov, Frederic Gibou Directed Self-Assembly is an important process used in the semi-conductor industry. It uses confinement masks to drive the self-assembly of block copolymers towards targeted nano-templates for subsequent optical or e-beam lithography. The shape of such confinement masks must be carefully designed as it is one of the primary factors determining the final polymeric structures. In this talk, we present a computational approach, within the self-consistent field theory framework, for finding confinement shapes that lead to a-priori chosen self-assembled structures of block copolymers. The method is based on a constrained optimization formulation described by partial differential equations: we define a cost functional that measures the discrepancy between the target and the actual self-assembled configurations, and analytically derive the sensitivity of the functional to changes in shape, which in turn enables an efficient minimization of the functional with respect to the confinement shape. We provide simulation results that demonstrate the ability of our approach to design mask geometries that successfully guide the self-assembly to the desired targets. |
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L70.00093: Coarse-Grained Simulations to Understand the Effect of Grafting on Methylcellulose Vaidyanathan Sethuraman, Kevin Dorfman Methylcellulose is a biopolymer derived from sugar, and it has a wide range of industrial applications. Recent experiments on methylcellulose solutions showed that they undergo fibril formation above the lower critical solution temperature. However, on grafting the methylcellulose polymer with polyethylene oxide (PEG), experiments show that the fibril structure is destroyed. We use coarse-grained molecular dynamics simulations to provide molecular insights into the effect of grafting on fibril formation. Our results showed that the radius of gyration of the polymer increases with increasing grafting density, in qualitative agreement with the experimental results. We also show that the loss in fibrillar structure arises from a steric repulsion between the grafted PEG monomers and the methylcellulose backbone. |
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L70.00094: A Coarse-Grain Model for Efficient Simulation of Self-Assembling Amyloidogenic Peptide Systems Murray Skolnick, Robert Riggleman, Zahra Fakhraai
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L70.00095: A Model for Hyaluronan Secretion into Biological Fluids Jan Scrimgeour
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L70.00096: Predicting the linear stress and dielectric relaxations of polydisperse linear polymers Daniel Read, Chinmay Das We present a generic algorithm to predict the linear relaxation spectrum for polydisperse linear polymers. As common in the tube theory descriptions of linear polymers, we assume that the stress relaxation is affected by both constraint release and tube escape modes. But unlike most existing descriptions, we consider how these two modes of relaxation affect each other and argue that the proper description for relaxation in an arbitrary blend of linear polymers requires consideration four embedded tubes affecting the different relaxation pathways: the thin tube, the tube for fastest reptation, the constraint release "supertube" and the fully diluted tube. We derive the scaling level descriptions of these relaxation pathways and use a large number of existing experimental results on the stress and dielectric relaxations to validate our model. For the particular case of binary blends of long and short polymers, our model is successful at predicting the linear stress and dielectric response for blends throughout the two dimensional space (constraint release rate and degree of entanglement) mapped by the Viovy diagram. |
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L70.00097: Impact of divalent ions on the rheology and aggregation of semidilute polyelectrolyte solutions Carlos Lopez, Walter Richtering We report rheology and light scattering data for the Na+, Mg2+, Ca2+, Mn2+, Co2+, Ba2+ salts of carboxymethyl cellulose in aqueous solutions. The viscosity as a function of molar polymer concentration falls into a single curve for all divalent salts. Compared NaCMC, divalent salts display a lower viscosities at low concentrations (in the non-entangled regime), suggesting less expanded chains. Above the entanglement crossover, solutions with divalent counterions display viscosities an order of magnitude larger than NaCMC because interchain crosslinks form by electrostatic bridging. |
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L70.00098: Viscoelastic Relaxation Behavior of Polyelectrolyte Complexes from Coacervate to Precipitate Samim Ali, Anand Rahalkar, Juan De Pablo, Vivek Prabhu The relaxation dynamics of polyelectrolyte complexes slows down while transitioning from coacervate to precipitate upon decreasing salt concentration. However, knowledge of such changes over full relaxation spectrum is still limited. This presentation will describe the relaxation behavior of complexes probed over a wide timescale by measuring viscoelastic spectra and zero-shear viscosities at varying temperatures, salt concentrations and molecular weights using a set of model polyelectrolytes. Our studies show that the complexes exhibit time-temperature superposition (TTS) at all salt concentrations, while the range of overlapped-frequencies for time-temperature-salt superposition (TTSS) strongly depends on the salt concentration and gradually shifts to higher frequencies as the complex approaches precipitate phase. Further understanding of this transition using the sticky Rouse model and simulations studies will be presented. |
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L70.00099: Free Surface Flows and Extensional Rheology of Polymer Solutions Jelena Dinic, Leidy Nallely Jimenez, 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 |
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L70.00100: Electronically excited states in p/p stacking compounds Ayaka Terauchi, Atsune Mitsui, Azusa Muraoka In particular, p/p stacking compounds have become of interest in new materials for photocatalysis, solar energy and phosphorescent organic light-emitting diodes. We investigate theoretically the photo-induced charge transfer in supramolecular chemistry such as a bowl-shaped polycyclic hydrocarbon and helical ortho-position linked phenylenes (OPs). The electronically excited states and absorption spectra of these materials were first studied by using TD- DFT calculations with various functionals. The functional that best reproduced the experimental results was found to be wB97XD, and the assignment of the experimentally observed UV-Vis absorption spectrum was successfully performed in comparison with the theoretically obtained one. We especially performed spectral assignment of the carbazole (Cz) -modified OP complexes. The results showed that the absorption spectrum of the complexes consisted of (i) an n–p* charge-transfer type transition from Cz to OPs units of longer wavelength at around 290 nm and the p–p* transition of a shorter wavelength at around 230 nm, and (ii) the components of three isomers which coexist with three kinds of substitution of Cz to OPs, such as ortho, meta and para linkage of Cz, to interconnect the aromatic units of the Ops. |
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L70.00101: Deformation of Hybrid Networks Michael Jacobs, Heyi Liang, Andrey Dobrynin Mimicking the mechanical properties of soft materials and biological tissues is crucial for novel materials development for medical implants, tissue engineering, soft robotics, and wearable electronics. Bottlebrush and comb networks are shown to be able to replicate the required combination of softness, strength and toughness in solvent-free elastomers. Such networks are made by crosslinking the side chains which results in the formation of the hybrid networks which have two types of strands of different rigidity and extensibility. We use a combination of analytical calculations and coarse-grained molecular dynamics simulations of hybrid network deformation to establish universal features. In our approach we first study an idealized system which preserves the network topology and represents the difference in the strands’ bending rigidities by considering the network strands as linear polymer chains with different Kuhn lengths and degrees of polymerization. The developed model is used to describe deformation of bottlebrush and comb networks in the linear and nonlinear network deformation regimes. |
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L70.00102: Comparison of Mullins Effect between Tough Double Network Hydrogels and Filled Elastomers under Various Types of Deformation Thanh-Tam Mai, Takahiro Matsuda, Tasuku Nakajima, Jian Ping Gong, Yoshihiro Morishita, Kenji Urayama The distinctive features of the Mullins effect between the double network (DN) hydrogels (Mai et al., Macromolecules 51, 5245–5257, 2018) and filled elastomers (Mai et al., Soft Matter 13, 1966–1977, 2017) are revealed by cyclic stretching measurement with various extension modes, i.e., uniaxial, planar, unequal and equal biaxial stretching. The modulus reduction, energy dissipation (D), and dissipation factor (Δ, the ratio of dissipated energy to input strain energy) in each loading-unloading cycle are evaluated. The result indicates that the cross-effect of strains (λiλj; i,j =x,y,z and i ≠ j) on Δ is pronounced in the DN gels whereas it is minimal in the filled elastomers. Interestingly, the modulus reduction relative to initial modulus and Δ in each cycle almost agree with each other in the DN gels, but they are considerably different in filled elastomers. This discrepancy reflects that the modulus reduction and dissipation factor are different in the main origin for the filled elastomers, while both of them totally stem from the purely elastic fracture of the chains in rigid and brittle DN gels networks. |
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L70.00103: Effect of miscibility on shape memory characteristics of Polymer Blends Surbhi Khewle, Pratyush Dayal Designing programmable shape shifting materials has been a grand challenge for science and engineering. Shape Memory Polymers (SMPs) are smart materials that have the ability to transform back to their intended shape when the external conditions are reversed. One of the strategies for synthesizing SMPs is to bond soft and rigid chemical moieties with one another through polymerization. Although polymer blending offers a simple strategy, it has not been used as a preferred technique to design SMPs. As most of the polymer blends are immiscible, synthesizing SMPs through blending route introduces a new set of challenges. Here, we use the equilibrium phase diagram to examine the role of compatibility of the constituent polymers on the characteristics of SMP blend. Specifically, we use Flory-Huggins theory in conjunction with the phase-field theory to capture the amorphous-amorphous and crystal-amorphous interactions in the SMP blends, respectively. Subsequently, we use the thermo-mechanical constitutive model to demonstrate the effect of miscibility on shape fixity and shape recovery of the SMP blend. Our approach can be utilized to design SMP blends with tunable properties and allows a mechanism to establish structure-property relationships in these systems. |
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L70.00104: Ion Specific, Odd-Even Glass Transition Temperatures in Precise Network Polymerized Ionic Liquids Christopher Evans, Chengtian Shen, Qiujie Zhao Relationships between Tg, fragility, nanostructure, electrostatics and conductivity are investigated in precise network polymerized ionic liquids (n-PILs). These n-PILs contain an exact number of carbon atoms (Cx) between charges in the backbone and can be exchanged to various anionic forms. The Tg exhibits an odd-even effect with the non-spherical, bulky bis(trifluoromethane sulfonamide) (TFSI) counter ion with a maximum jump of 45 K between C4 and C5 networks. In contrast, the same n-PIL networks with the smaller and spherical BF4 anion show no odd-even Tg effect. Small angle X-ray scattering of TFSI networks suggests that ionic aggregation is not the primary cause of the odd-even effect. The amorphous halo exhibits a weak odd-even dependence indicating a minor role of backbone-backbone correlations and packing on the observed effects. However, odd-even effects appear to be largely dynamical in n-PILs with only minor variations in structure. Due to the large changes in Tg, the room temperature ionic conductivities of the TFSI n-PILs exhibit odd-even effects greater than an order of magnitude between adjacent Cx networks. Finally, dynamic fragility shows odd-even fluctuations with higher fragility corresponds to lower Tg, opposite to what is typically observed. |
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L70.00105: Efficient Shockwave Energy Dissipation in Dynamic Covalent PDMS Rubber Christopher Evans, Jaejun Lee, Brian Jing, Laura E Porath, Nancy Sottos Polymer networks containing transient bonds require some amount of energy to undergo an exchange process. We hypothesize and demonstrate that dynamic bonds in polydimethylsiloxane (PDMS) networks can be used as an effective mechanism for dissipating shockwave energy. By controlling the diol molecular weight, the density of dynamic boronic ester linkages can be controlled while the network chemistry is invariant. Using a classical laser induced shockwave technique, we demonstrate superior energy dissipation in a PDMS boronic ester dynamic rubber (PDMS-B-DR) compared to the benchmark polyurea and covalent PDMS (cured via thiol-ene click chemistry). A monotonic improvement in dissipation performance (monitored as a reduced peak pressure of the shockwave) is observed with increasing density of dynamic boronic ester bonds. In all cases, the Tg is invariant in the different networks (-125 °C) implying a minimal role of segmental dynamics on dissipation in these specific networks. Our results indicate that dynamic networks are a promising route to engineering improved SWED materials which are lightweight, flexible, and able to withstand repeated shocks. X-ray scattering and rheology have also been performed to relate dissipation performance to structure and relaxation of the material. |
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L70.00106: Approaches to Modification of Maleic Anhydride Copolymers with Applications to Antifouling and Water Purification Steven Zboray, Kirill Efimenko, Jan Genzer Precise control over structure and tailoring of chemical moieties along the chain are the keys to creating polymeric materials with advanced functionality. We present an approach based on maleic anhdyride copolymers allowing facile modification with various chemical groups as embodied in two systems: a polymer network capable of catalytic degradation of organophosphates and antibiofouling coatings. Through the use of crosslinking, which could be controlled via several synthetic pathways, hydrogels containing hydroxamic acid groups were made that allowed the gel to be used for water purification applications. Kinetic studies of the performance of the gels in degrading the model compound dimethyl nitrophenyl phosphate (DMNP) were performed. For antifouling purposes, a systematic study of the structure-property relationships of several sulfobetaines and the ability to resist fouling by fluorescent-labeled proteins was conducted. It was also found that by varying the comonomer in the system, it was possible to control hydrophobic/hydrophilic interactions and adhere the polymers to substrates as thin-layer coatings. |
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L70.00107: Elastocapillary-driven Deposition of Liquid Drops in Polymer Gels Hongbo Fu, Christopher Barney, XUDONG LIANG, Alfred Crosby The deposition of a finite volume of liquid at a specific location within an elastic gel offers novel opportunities for device fabrication and materials properties measurement. We present a systematic study of the controlled deposition of liquid droplets within a polymer hydrogel. With parameters, such as pressure and viscosity of the liquid, the size and spacing of deposited liquid droplets can be controlled. To understand this process, we propose an elastocapillary-based mechanism that balances the surface tension and viscosity of the liquid with the elasticity of the gel. |
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L70.00108: Finite element modelling of polymer gels that exhibit temperature induced volume phase transitions Priyanka Nemani, Ravi Sastri Ayyagari, Pratyush Dayal Temperature-induced volume phase transitions are one of the mechanisms by which large-scale deformations are manifested in biological systems. Polymer hydrogels that undergo spontaneous volume change upon variations in temperature are, therefore, perfect candidates for designing bioinspired self-oscillating materials that can reversibly sustain large deformations. Here, we present a computational framework to design the dynamical system based on chemical reactions, that undergoes large mechanical oscillations via external loading and thermally induced volume phase transitions, simultaneously. Specifically, our model is based on a nonlinear finite element framework that essentially combines reaction-diffusion phenomena with nonlinear elastic deformations of the gel under nonisothermal conditions. Through modelling and simulation, we capture large deformations and volume changes represented by swelling/shrinkage of the gels at varied temperatures. Our major findings not only complement the existing features of polymer gels and facilitates the design of a variety of complex biomimetic systems like thermo-sensitive actuators but also provides a mechanism to predict their complex nonlinear phenomena. |
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L70.00109: Diffusion of Gold Nanoparticles in Entangled Poly (vinyl alcohol) Solutions and Gels. Kavindya Senanayake, Ashis Mukhopadhyay Dynamical studies of nanoparticles in concentrated polymer solutions have importance in industrial and medical applications. We study the diffusion of gold nanoparticles (AuNPs) in high molecular weight poly (vinyl alcohol) (PVA) entangled solutions and gels. Using fluctuation correlation spectroscopy, diffusion coefficients of different sized AuNPs in different volume fractions above the entanglement volume fraction of PVA were determined. Comparison of results with the recent scaling theories will be presented. |
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L70.00110: Computational investigation of cavitation phenomena in physically assembled gels Satish Mishra, Thomas E. Lacy, Jr, Santanu Kundu Cavitation rheology is a novel technique to probe local mechanical properties of soft materials. In this experiment, a defect is introduced in the gel by inserting a needle connected to a syringe pump. The growth of defect subjected to a pressure load is recorded. At critical pressure, the defect becomes unstable and suddenly expands into a cavity leading to a drop in pressure. For physically assembled gels, experimental studies demonstrate critical pressure as high as ten times of that calculated analytically using hyperelastic models. We present a finite element modeling approach to capture the coupled effect of material modulus, viscous dissipation, surface tension, and geometry confinement in determining the critical pressure. Our results indicate that a portion of pressure applied to expand the defect dissipates through stress relaxation mechanism, thus, pumping rate influences the critical pressure. Surface tension restricts the expansion of defect while the confinement introduces an artificial stiffening response to the gel, hence, increase the critical pressure. We will also compare the finite element analysis results with that obtained from cavitation experiments. |
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L70.00111: Polyethylene Cross-link Density Effects on Crystallization and Shape Memory Performance Dean Penner, Chesterton B Schuchardt, Audrey T Young, David D Hsu In pursuit of a model of microstructure-property relationships in cross-linked, semi-crystalline Shape Memory Polymers (SMPs), we investigate the effect of cross-link density on thermally-activated SMP performance characteristics. Specifically, we aim to establish a relationship between crystal size distribution and shape fixity, shape recovery rate, and shape recovery temperature. United-atom Molecular Dynamics (UAMD) simulations of the shape memory cycle for cross-linked polyethylene are carried out at varying cross-link densities between 150 and 800 g/mol. Crystal size distribution is investigated as a function of cross-link density using order parameter and a density-based clustering algorithm. Both shape fixity and shape recovery rate are found to increase with lower cross-link density down to 150 g/mol, due to the uniform crystal size distribution resulting from unimpeded crystal growth. |
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L70.00112: Bioinspired Fast Motion of an Elastomer Bilayer Beam Michelle Gee, Justin Glover, Jonathan Pham While plants are traditionally regarded as static, some plants are able to move at accelerations thousands of times the acceleration of gravity. Engineered systems seek to achieve the high accelerations and high speeds observed in nature for use as fast and adaptable materials. Using the inspiration of plant seed pods, we aim to demonstrate that adhesion may act as self-releasing latch when sufficient bending energy is applied to overcome the adhesion of the latch, causing rapid energy release in the form of a bending motion. We prepare a bilayer beam made of polydimethylsiloxane (PDMS) layers with different crosslinking densities, which provides a mechanism for asymmetric swelling and bending when placed in good solvents. Our actuator approaches accelerations 20 times that of gravity and with total response times on the order of 10 ms over cm-scale distances. This work is one step towards increasing the abilities of soft actuators and robots capable of fast motion that are not limited by the requirements of mechanical motors. |
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L70.00113: Water Dynamics in Poly(N-isopropyl acrylamide) Solutions at Ambient and High Pressure Probed with Quasi-elastic Neutron Scattering Bart-Jan Niebuur, Wiebke Lohstroh, Marie-Sousai Appavou, Alfons Schulte, Christine M. Papadakis We investigate the dynamic behavior of hydration water in a 25 wt% aqueous Poly(N-isopropyl acrylamide) (PNIPAM) solution in dependence on temperature (25 – 50 oC) and pressure (0.1 – 130 MPa) employing quasi-elastic neutron scattering (QENS). The susceptibility spectra span the frequency range from 2 GHz to 2 THz at momentum transfers between 0.7 to 1.7 A-1 and reveal the relaxation peak of the hydration water near 10 GHz, in addition to the known diffusive and effective local and vibrational processes of bulk water. Evaluating the temperature dependence, we find that, at atmospheric pressure, the relative population of (bound) hydration water sharply decreases upon heating from the one-phase to the two-phase state, i.e. the chains dehydrate strongly. In contrast, at 130 MPa, no sharp decrease is observed, i.e. the dehydration takes place over a much broader temperature range. This suggests an enhanced hydrophobic hydration at high pressure. |
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L70.00114: Biomimetic wet-applicable adhesive as a stiffness-tunable binding interface for on-skin sensors and self-locking actuators Song Chen, Songshan Zeng, Lan Liu, Luyi Sun Both stimuli responsive strain sensors and actuators have drawn significant attention because they are promising in a wide span of applications, including wearable devices, stretchable electronics, and soft robotics. However, there are few researches focusing on achieving a wet-applicable, ultra-conformable, and stiffness-tunable interface, which is highly critical in these fields. Herein, we develop a novel wet stretchable adhesive that shows high binding strength to various substrates. Furthermore, by introducing hygroscopic calcium chloride (CaCl2) into the system, the Young’s modulus of the adhesive film can be easily adjusted from higher than 1.5 GPa to lower than 0.01 MPa under ambient environment (ca. 25 °C, 70% relative humidity) because of the water uptake and the corresponding plasticizing effect. We further use this adhesive to fabricate a soft (skin-like modulus, 0.1-10.0 MPa), thin (~50 μm), highly sensitive (a gauge factor of ~2000 under 20% strain), and ultra-compliant on-skin strain sensor and a multi-responsive (heat, near infrared (NIR) light, voltage, and humidity) self-locking actuator. A new avenue has been created to address both sensing and actuating bottlenecks by introducing a wet-applicable adhesive as a versatile and robust binding interface. |
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L70.00115: Spinodal Decomposition-Induced Surface Wettability Modification of Thermo-Responsive Nanoemulsion Films HYEMIN SEO, Jin Woong Kim Functional polymer thin films with a multilayer structure have been constructed with nanometer scales typically by using the sequential adsorption of oppositely charged polyelectrolytes onto a solid substrate. Tight control over phase separation is essential for providing the film with structured surface heterogeneity as well as surface functionality. Herein, we fabricate nanoscale emulsion thin films by utilizing the layer-by-layer deposition. Their thickness was tunable to micrometer scales by solely changing the number of alternate emulsions and polyelectrolytes layers. Interestingly, the nanoemulsion films exhibited a thermos-responsive heterogeneous phase separation behavior, which is typically referred as Spinodal decomposition. We observed that surface wettability of the Nanoemulsion films was critically dependent upon the pattern of the Spinodal decomposition, which enables development of thin film-based smart drug delivery patches. |
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L70.00116: Towards Optimizing Synthesis Temperature for Microgels with Large Degree of Deswelling Kiril Streletzky, Krista G Freeman, Jacob Adamczyk Polysaccharide microgels have been synthesized at various temperatures (Tsyn) above the LCST of the parent polymer. Microgel structure and dynamics below and above the corresponding volume phase transition have been studied with light scattering. All microgels were found to undergo a reversible 15-50-fold deswelling in volume. However, the size distribution, structure, dynamics, and deswelling ability of microgels were found to strongly depend on synthesis temperature. In this work, the attempt was made to optimize the synthesis temperature to yield more monodisperse microgels with a larger degree of deswelling. The results suggest that Tsyn influences the density distribution of microgels and, therefore, their structure and dynamics. |
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L70.00117: Effect of Elasticity, Viscosity, External Dissipation and Structures on Impulsive Elastic Energy Release in Polymers XUDONG LIANG, Alfred Crosby Impulsive elastic energy release in materials have been widely adopted in small organisms and engineered micro-robotic devices to achieve high speed motion. The kinematics of impulsive motion are well characterized through high speed camera imaging, but the mechanics of the materials under large deformation and high strain-rate deformation is not yet established. Here, we present a theoretical and experimental study about the effects of material properties, environmental interactions and structures of synthetic polymers for the performance of a free retraction. Building upon the 1D elastodynamics and nonlinear mechanics, we discover that kinematics of impulsive recoiling can be described through a power-law constitutive model, and the residual strain after retraction determines the maximum center-of-mass velocity. The viscous losses in the materials and frictional force in the environment are shown to significantly affect the center-of-mass velocity. Finally, we explore how topologies in mechanical metamaterials can lead to control of impulsive elastic energy release. |
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L70.00118: Microballistic Deformation Behavior of Carbon Nanotube Mats Wale Lawal, Jinho Hyon, Ramathasan Thevamaran, Edwin Thomas We investigate the energy absorption characteristics of 2D isotropic multiwall carbon nanotube (MWCNT) mats using a micro-projectile impact test at velocities ranging from 300 m/s to 900 m/s . The quasi-static properties of the 2D isotropic network of meandering MWCNT nanofibers are quite modest but at the extreme strain rates and large strains of ballistic impact, the deformation behavior of the mat results in unprecedented energy absorption per unit mass of the target mat. The mat is comprised of a network of ultra high aspect ratio interconnected tubes and tube bundles with many branches and cross-overs leading to increasing retarding forces from the interacting tubes and tube bundles with the silica sphere projectile. As the projectile rotates and moves forward, the MWCNT tubes and tube bundles are straightened and pulled into the impact region. The increased friction associated with the amplified surface interactions occurring between the translating principal tubes raises the load on those portions of the tubes adhering to the sphere surface and the subsequent large back-deflection of the impact region slows the advancing projectile as KE is converted into elastic stretching energy of the network and ultimately fracture of many principal tubes. |
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L70.00119: Slicing of soft materials Steven Rhodes, Eric Weeks We experimentally study the slicing of soft materials. We use a rheometer to press a circular cutting tool into materials (a steel “cookie cutter”). This allows us to measure the normal force required to press the cutter and the torque required to rotate the cutter, while controlling the shear rate. Our soft materials are Styrofoam and PDMS. We find rotating the cutter makes it easier to cut into the material. In particular, without rotation, the cutter only indents the Styrofoam rather than slicing it. |
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L70.00120: Optimizing random heteropolymers to improve protein folding in cell-free synthesis Zhiyuan Ruan, Tao Jiang, Ting Xu Membrane proteins play key roles in biological activities, and represent one of most prevailing drug targets. Functional and structural analysis of membrane proteins remain intriguing but challenging due to the protein misfolding and aggregation. Here, we show that four-monomer random heteropolymers (RHPs) can assist membrane protein folding during translation in cell free synthesis. Two types of membrane proteins, Aquaporin Z (water channel,helices) and OmpT (protease, barrel) were examined, and demonstrated tunable polymer performance by controlling the composition of RHPs. The results indicated that the extent of folding assistance of various RHPs for the membrane proteins was different due to the chemical heterogeneity along the length of RHP chains. An in-house program for chemical heterogeneity analysis was developed to investigate the sequences of various RHPs and proteins. The current data suggests that RHPs act as artificial chaperones and that their ability to aid in the proper folding of membrane proteins can be easily tuned by changing their composition. |
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L70.00121: Thickness-dependent elastic modulus of spin-coated PDMS films Pak Man Yiu, Hailin Yuan, Ophelia Tsui Poly(dimethyl siloxane) (PDMS) elastomer is one of the most commonly used substrate materials for stretchable electronics and artificial skin. Many fundamental studies of soft interface mechanics use PDMS. It is therefore important to understand the factors affecting the mechanical properties of this material. A previous study revealed that the elastic modulus, E, of spin-coated PDMS increased almost three-fold when the PDMS thickness, h, was decreased from 108 to ~30 μm. The enhancement in E had been attributed to the alignment of PDMS chains during spin-coating. In this study, we measured the elastic modulus of spin-coated PDMS with various h from 15 to 110 μm. We found that E increased with decreasing h initially, but on reaching h ~ 20 μm, E decreased with decreasing h. We verified that this phenomenon was universal regardless of the curing condition. We discuss a possible origin for the phenomenon with supporting measurement data. |
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L70.00122: Force Balance at Contact Lines of Soft Substrates Heyi Liang, Zhen Cao, Zilu Wang, Andrey Dobrynin We use coarse-grained molecular dynamics simulations to show that the force balance analysis at the triple-phase contact line formed at an elastic substrate must include a quartet of forces: three surface tensions (surface free energies) and an elastic force per unit length. In the case of the contact line formed by a droplet on an elastic substrate, the elastic force is due to substrate deformation generated by formation of the wetting ridge. The magnitude of this force fel is proportional to the product of the ridge height h and substrate shear modulus G. Similar elastic line force should be included in the force analysis at the triple-phase contact line of a solid particle in contact with an elastic substrate. For this contact problem elastic force obtained from contact angles and surface tensions is a sum of the elastic forces acting from the side of a solid particle and an elastic substrate. By considering only three line forces acting at the triple-phase contact line, one implicitly accounts the bulk stress contribution as a part of resultant surface stresses. This “contamination” of surface properties by a bulk contribution could lead to unphysically large values of the surface stresses in soft materials. |
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L70.00123: Effects of force on facilitated protein dissociation Jing Zhao, Katelyn Dahlke, Charles E. Sing Protein-DNA interactions depend on the conformation of DNA, so binding/unbinding kinetics may be altered by applied forces; classically, protein unbinding is accelerated and binding is inhibited as force increases. Additionally, certain proteins exhibit concentration-dependent dissociation rates, where proteins in solution compete to facilitate protein dissociation from DNA. Together, facilitated dissociation (FD) and force can lead to diverse dissociation behaviors including “slip bonds”, where dissociation rates decrease with force, and “catch bonds”, where dissociation rates increase with force. We investigate these combined effects via coarse-grained simulation. We reproduce concentration-dependent rates that are observed experimentally and explore how force can alter these binding kinetics. We observe catch bonds when protein binding is strongly coupled to the force, while the force dependence of protein unbinding is relatively weak. Slip bonds occur under opposite conditions. Transitions between these different bonds occur when force effects on binding and unbinding compete. Thus, applied force may regulate protein-DNA interactions by inhibiting FD by coupling protein exchange rates to DNA conformations. |
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L70.00124: Melt-Electrospinning of Poly(ether ether ketone) Fibers to Avoid Sulfonation Nelaka Dilshan Govinna, Thomas Keller, Peggy Cebe We have successfully electrospun un-sulfonated fibers of poly(ether ether ketone), PEEK, from the molten state. A high temperature furnace was used to melt electrically grounded PEEK pellets at 350 °C, and the electric force caused fibers to be deposited onto the high voltage collector. Whereas solution electrospinning of PEEK results in sulfonation of the polymer chain and reduction of thermal stability, direct melt electrospinning produced PEEK fibers which are chemically unaltered from as-received pellets, as shown by their Fourier transform infrared spectra. Thermogravimetry demonstrated electrospun PEEK fibers have similar thermal decomposition temperature, Td = 600 °C as the pellets. Melt electrospun fibers had a large range of diameters, ranging from 1.5 μm to 8.5 μm, and were smooth, defect-free, and round in cross-section. As-spun amorphous fibers, with thicknesses less than 10 μm and masses ~200 ng, were selected for fast scanning calorimetry (FSC) experiments. Using heating and cooling rates from 50 to 2000 K/s, FSC studies were made of the glass transition, melting and crystallization behavior of electrospun PEEK fibers. |
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L70.00125: Structural differences in regenerated cellulose fibers produced using Viscose and Lyocell techniques Aakash Sharma, Guruswamy Kumaraswamy, Shirish Thakre We compare the structural features of regenerated cellulose fibers manufactured using Viscose and Lyocell processes. It is known that these fibers possess different surface morphologies. However, there is not much information on nanoscale structural features e.g. microvoids, lamellar structure etc. We show using small angle x ray and ultra-small angle neutron scattering that the fibers possess elongated microvoids, oriented in the fiber direction. We analyse 2D SAXS data using Ruland’s equatorial streak method and obtain average length and average misorientation of the microvoids in both fibers. Using Porod’s law and invariant calculated from the combined SAXS and USANS measurement, we evaluate the radius. We show that Lyocell fibers have bigger, better orientated voids than Viscose fibers. There are also differences in the crystal structure of these two fibers. Scattering from Viscose fibers show evidence for lamellar stacking in the fiber direction whereas, that from the Lyocell fibers is qualitatively different and does not show stacking. This shows that process differences strongly affect the microstructure of the fibers at length scales of few nanometres. |
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L70.00126: A molecular model for ductility (T< Tg) and drawability (T>Tg) of semicrystalline polymers Shiqing Wang, Masoud Razavi We make oversimplifications to construct a tractable molecular model for mechanics of semicrystalline polymers that takes into account of the mechanical interplay between crystalline and amorphous regions connected by tie chains. The idea can be reformulated to address the origin of yielding or breaking in semicrystalline polymers that form spherulites. Our goal is to understand the brittle failure of fully crystallized glassy polymers such as PLA and PET and whether or not various semicrystalline polymers are highly drawable above their glass transition temperatures. |
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L70.00127: Semiflexible Polymers in Spherical Confinement Arash Nikoubashman, Andrey Milchev, Mihir Khadilkar, Sergei Egorov, Daniel Vega, Kurt Binder Semiflexible macromolecules find various applications as versatile materials, in particular due to their possible liquid crystalline order, and are also important constituents of living matter. We studied the ordering of such stiff macromolecules confined in spheres by molecular dynamics simulations, and found that densely packed semiflexible polymers cannot exhibit uniform nematic order when their contour length is of the same order as the sphere radius. Instead, the confinement leads to the emergence of topological defects on the sphere surface with competing ordering in the interior of the sphere. Each of the configuration variables including chain length, chain stiffness, packing density, and shell thickness uniquely affect the ordering, including the nature and relative orientation of the defects on the surface. For example, at high densities, a thin shell of polymers close to the surface exhibits a quadrupolar tennis ball texture due to the confinement-induced gradual bending of polymer bonds. Systemic trends observed could pave the way for better understanding the links between topological defects and elastic properties of polymers. Further, controlling the defect locations is promising for designing patterned colloids in experiments by functionalizing defect sites. |
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L70.00128: Replicating Chiral Structures with Common Polymers and the Sudy of Surface Changes under VOC’s Thomas Stoke, Petr Shibayev Liquid crystals are known to have interesting surface patterns, characterized by focal conic domains patterned across their surface. These chiral structures can be observed through Atomic Force Microscopy, and replicated on the surfaces of common polymers. When exposed to certain Volatile Organic Compounds (VOC’s), the surface structures of chiral polymers are seen to break down. However, on these replica polymers, no such changes can be seen. The applications of these traits are discussed. |
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L70.00129: Dynamic Relaxation and Glass Transformation of Electrospun Fibrous Membrane with Confined Chain Configuration: for Physical Aging and Shape Function Control and Delivery Bin Xiao, Chenhong Wang, Nuozi Zhang, Heran Wang, Xuhong Chen, Shanshan Xu, Charles C Han The thermodynamic glass transformation processes of electrospun membranes are firstly introduced to study the dynamic relaxation nature of this not always in equilibrium transformation process. The relaxation modes of the electrospun membrane are slow but measurable in the vicinity of the Tg and even above the Tg due to the stretched chain in long distance. Based on the differential scanning calorimetry (DSC) experiments and the general principle of mode-coupling theory (MCT), the endothermic peak temperature and the relaxation enthalpy were used to analyze the relaxation process by capturing these instantaneous "arrested" structures. With different annealing time and annealing temperatures relative to DSC measured T for E-spun membrane with different molecular weight, the short and long wavelength relaxation modes could be identified. These results clearly show the dynamic nature of the glass transition in polymeric materials which can be explained by the general principle of MCT type of dynamic theory. |
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L70.00130: Terahertz Dynamics of Carboxymethyl Starch Wakana Terao, Leona Motoji, Tatsuya Mori, Karolina Kaczmarska, Beata Grabowska, Yasuhiro Fujii, Akitoshi Koreeda, Mikitoshi Kabeya, Jae-Hyon Ko, Seiji Kojima We performed terahertz time-domain spectroscopy on microwave-treated sodium carboxymethyl starch (CM-Starch), to detect the boson peak and fracton. Starch is a natural polymer formed by polymerization of a number of D-glucose molecules by glycosidic linkage and CM-Starch is produced by carboxymethylating the starch. The obtained spectral shape of boson peak plot α(ν)/ν2 of the CM-Starch, where α(ν) is the absorption coefficient, is different from vitreous glucose. It suggests the existence of the fracton in the CM-Starch. |
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L70.00131: Contrasting rubber-toughen mechanisms for glassy polymers Masoud Razavi, Shiqing Wang, Hailan Guo We perform standard pre-yield and post-yield stress relaxation to probe molecular mobility in various rubber-toughened polymer glasses and to differentiate between “apparent” and true yielding. The rubber-toughened PS and SAN, e.g., HIPS and ABS, show apparent yield at high strains whereas a new generation of PMMA based nanocomposites from Dow Chemical is transparent, truly ductile and shows enhanced molecular mobility in post-yield deformation at different draw rates, form a sharp contrast with the conventional materials such as HIPS and ABS. |
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L70.00132: The morphology and flowing behaviors of TEMPO-oxidized cellulose nanofibers dispersed in non-aqueous solutions Ruifu Wang, Tomas Rosen, Chengbo Zhan, Benjamin S Hsiao Cellulose nanofibers (CNF), sustainable and possessing good mechanical properties, is a good reinforcement agent for polymer composites. However, pure CNF is hard to disperse in common organic solvents due to the strong inter-fibrillar H-bondings and van der Waals interactions. In this study, we investigated the dispersion behavior of CNFs having different charged density, prepared by the TEMPO-oxidation and nitro-oxidation methods, in two different non-aqueous solvents: ethylene glycol and propylene glycol. The morphologies of CNF was first characterized by combined AFM, TEM and solution SAXS methods, whereby the results showed that the fiber cross-section dimensions were closely related to the oxidation conditions that also led to different charge density. The rheological results indicated that the overlap concentration of the suspension is solvent independent. Moreover, the CNF/glycol suspensions behave very similarly to polymer solutions, exhibiting shear thinning behavior beyond the overlap concentration. We postulate that the solvent exchanging method could also be used to disperse CNF into other non-aqueous solvent for better mixing with hydrophobic polymers. |
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L70.00133: Polymer physics and flow dynamics of thermodynamically pure ring polymers Michael Tu, Ching-Wei Lee, Christopher Rudolphi, Simon Rogers, Charles Schroeder Ring polymers have fascinated polymer chemists and physicists for decades, yet achieving a complete understanding of the dynamics of pure ring polymer systems has remained elusive due to major challenges in residual linear polymer contamination. Despite recent advances in purification methods, trace amounts of linear polymers are thought to remain in existing ring polymer samples, greatly affecting the mechanical properties of these materials. Here, we study the equilibrium and non-equilibrium flow properties of synthetic rings based on cyclic poly(phtalaldehyde) (cPPA), a low-ceiling temperature polymer whose linear chain analogues are thermodynamically unstable at room temperature due to depolymerization at free ends. The polymerization reaction yields high molecular weight cyclic polymers with no free ends, thereby providing highly pure and thermodynamically stable ring polymers. Using this approach, we study the linear viscoelastic properties, zero-shear viscosity, and nonlinear flow response of cPPA samples as a function of polymer molecular weight and weight fraction. Overall, these results give insight into the dynamics of ring polymer systems with unprecedented purity. |
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L70.00134: Nonlinear melt rheology explored by molecular dynamics simulations Yexin Zheng, Mesfin Tsige, Shiqing Wang We apply bead-spring based molecular dynamics simulation to study both shear and extensional responses of entangled melts. Shear creep is carried out to show the emergence of entanglement-disentanglement transition (EDT) previously observed in experiment [1], confirming that EDT can take place in absence of edge instability. At high Rouse-Weissenberg numbers (larger than ca. 5), entangled melt is observed to undergo melt rupture independent of whether Filament stretching rheometry or Sentmanat extensional rheometry is employed. The lack of yielding suggests intriguing lockup of chain entanglement in melt stretching [2]. Such extreme tensile strain localization is observed for the first time in MD simulation, corresponding to the threshold of full chain disentanglement in absence of the chain scission mechanism that in reality triggers the unzipping of chain entanglement. |
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L70.00135: Melt Blown Cross-linked Fibers from Thermally Reversible Diels-Alder Polymer Networks Kailong Jin, Sung-Soo Kim, Jun Xu, Frank Bates, Christopher Ellison Melt blowing is a process in which liquid polymer is extruded through orifices and then drawn by hot air jets to produce nonwoven fibers. Melt blown nonwovens constitute more than 10% of the $50 billion global nonwovens market. Thermoplastic feedstock, such as polyethylene, polypropylene, and poly(butylene terephthalate), have dominated melt blown nonwovens because of their combined cost, good chemical resistance and high-temperature performance. Cross-linked nonwovens from other commodity polymers (e.g., (meth)acrylates, styrenics, silicones, etc.) could be attractive alternatives; however, no commercial cross-linked nonwovens currently exist. Here, cross-linked fibers were produced via one-step melt blowing of thermoreversible Diels-Alder polymer networks comprised of furan- and maleimide-functional methacrylate-based polymer backbones. These dynamic networks decross-link and flow like viscous liquids under melt blowing conditions, then revert to a network via cooling-induced cross-linking during/after melt blowing. Finally, the resulting cross-linked fibers can be recycled because of their reversible dynamic nature, which may help address the microfiber pollution problem. |
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L70.00136: Properties of chemically crosslinked methylcellulose gels Peter Schmidt, Svetlana Morozova, McKenzie Coughlin, S. Piril Ertem, Theresa M. Reineke, Frank Bates, Timothy Lodge Methylcellulose (MC) is used in an impressively wide variety of commercial products due to its ability to reversibly form fibrous networks upon heating. To investigate the effect of crosslinking on these materials, we have prepared two types of gels and compared their thermodynamic and elastic properties. First, crosslinked methylcellulose gels were prepared at room temperature using a thiol-ene click reaction. Allyl methylcellulose was crosslinked with dithiol poly(ethylene glycol) (M = 1500 g/mol) and allowed to swell to equilibrium as a function of temperature and strand length. Upon heating, instead of forming fibrous networks, crosslinked methylcellulose gels experience volume change. By measuring the polymer volume fraction and modulus of gels in equilibrium we identify the thermodynamic parameters that drive the gel volume change using a modified Flory-Rehner theory. Second, crosslinked methylcellulose fiber gels were prepared by crosslinking allyl methylcellulose solutions at 80 °C, after the full conversion of chains to fibrils. The swelling and thermodynamic properties of crosslinked chain gels and crosslinked fiber gels will be compared and discussed. |
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L70.00137: Gel Point Determination of a Diffusive Photopolymer via 1H NMR Relaxometry Casey Lee-Foss, Anthony V Lynch, Gretchen Hofmeister, Martha-Elizabeth Baylor Diffusive photopolymers can simplify the fabrication of “lab on a chip” devices. Knowledge of the gel point of the photopolymer, defined as the exposure time when an infinite macromolecule is formed, is required to create complex coplanar features via UV exposure. Because instrumentation for traditional gel point determination techniques is not locally accessible, we sought to develop a locally available method of gel point quantitation for a two-stage methacrylate/thiol-ene formulation. Since methacrylate chain growth and increasing cross-linking during the sol-gel transition reduces the mobility of diluent monomers, we hypothesized that the gel point can be found using NMR inversion-recovery to measure how polymerization affects the mobility-dependent T1 relaxation time of an added “spectator” molecule. We present results showing a correlation between the rheological gel point and the time when the slope of T1 versus exposure time changes, demonstrating 1H NMR relaxometry is a feasible method of gel point determination. |
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L70.00138: Self-Moving Polymer beads Ankur Mittal, Pratyush Dayal Self-propelled motion through internalized chemical reaction, a characteristic of living systems, has led to the design of various synthetic bio-inspired systems. Here, we design a self-moving macroscopic system through careful use of self-oscillating chemical reaction inside a polymeric gel. Specifically, we use poly-N-isopropylacrylamide (NIPAAm) gel bead as a miniaturized reactor and harness chemical oscillations of the Belousov Zhabotinsky (BZ) reaction to produce sustained motion. In a typical experiment, the gel beads are charged with BZ reagents and placed on an oil-covered substrate. Due to the porous nature of the gel beads, the intermediates of BZ reaction ooze out of the gel and react with oil, thereby producing spontaneous motion of the bead via Marangoni effect. We further demonstrate that the velocity of the beads can not only be controlled by tuning the kinetics of BZ reaction but also by varying the external stimuli. In particular, we show that by using Ru decorated graphene nanosheets as catalysts the velocity of the beads can be enhanced significantly compared to the traditional solution based catalysts. Our findings can be used to design self-propelled conveyor belts that can deliver cargo from micron to mm length scale. |
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L70.00139: Design of Self Oscillating Ionic Gels Sairam S, Arnab Dutta, Arvind Kumar, Pratyush Dayal
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L70.00140: Salt and Water Diffusivities in Polymer Electrolyte Membranes Dipak Aryal, Venkatraghavan Ganesan Motivated by experimental observation where transport properties of salt ions and water in charged polymer membranes exhibit an intriguing dependence on salt concentration, we have probed a series of atomistic molecular dynamics simulations of non-cross linked membranes in aqueous mono and divalent salt solutions along with mesoscale dissipative particle dynamics (DPD) simulations for crosslinked membranes at concentrations ranging from 0.06 to 1 M. We investigate the molecular level understanding the effects of both multi-component salt solutions and crosslinking of polymers on fundamental salt and water transport properties. Our finding shows that the diffusion of salt ions and water are influenced by cation sizes and salt concentrations. Divalent ions are more strongly coupled with ionic groups which reduce their motions as increasing concentration in fixed charged membranes. In crosslinked membranes, diffusion of salt ions and water are reduced significantly relative to non-crosslinked systems. However, the trends exhibited by the salt concentration dependence of diffusivities, and the coordination of the cations with anions, and with the polymer backbone remain qualitatively similar to those observed in non-crosslinked membranes. |
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L70.00141: Effect of doping ratio on lithium-ion conductivity in nanostructured self-doped block polymer electrolytes Melody Morris, Thomas H Epps Self-doped polymers, in which the salt anions are attached covalently to the polymer, are promising alternatives to salt-doped polymer electrolytes because concentration polarization is reduced and stability is enhanced in the electrolyte. A self-doped diblock terpolymer electrolyte was synthesized such that one block was composed of a high modulus material and the other block consisted of both ion-conducting and self-doping monomer segments. The self-doped block polymers were made with a series of self-doped lithium concentrations (by altering the relative amounts of ion-conducting and self-doping monomer segments). Small-angle X-ray scattering results suggested that all self-doped block polymers exhibited ordered nanostructures. AC impedance spectroscopy and DC polarization were used to evaluate the conducting properties of the electrolyte (ionic conductivity and transference number), and the conductivities increased with self-doping ratio. Thus, with the framework for nanostructured self-doped block polymer electrolytes realized, the ion content can be manipulated to design improved electrolyte systems. |
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L70.00142: Tailoring Ionic Conductivity of Block Copolymer Electrolytes with End-functionalized Homopolymers JIHOON KIM, Moon Jeong Park Block copolymer electrolytes based on poly(ethylene oxide) (PEO) have been regarded as promising candidates of solid electrolyte materials for lithium ion batteries. This is attributed to their ability to dissolve lithium salts and high ionic conductivity of the resultant polymer/salts complexes. However, PEO crystallization below its melting temperature has been tied to a radical reduction in ionic conductivity, especially at room temperature, various attempts have been made to reduce the PEO crystallinity. Herein, we propose a new method to modulate crystallization behavior of PEO-based block copolymers with embedded end-group-functionalized PEO homopolymers. Intriguing, the morphology and ionic conductivity of the resultant block copolymer/homopolymer blends were sensitive function of the type of end group in PEO homopolymers at the same blend ratio. Our approach offers a platform for the development of efficient solid-state polymer electrolytes by controlling intermolecular interactions in PEO phases via a simple end-group chemistry. |
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L70.00143: Ion clustering behavior of “precise” phosphonated polymers Se Jong Kang, Moon Jeong Park Polymers functionalized with phosphonic acid groups are promising candidates of proton exchange membranes for fuel cells that can be operating at high temperatures. This is owing to the amphoteric nature and self-dissociation ability of phosphonic acid groups, unlike sulfonic acid counterparts, thereby allowing acid groups to form hydrogen-bond networks in the absence of moisture. In the present study, we report the synthesis of polymers bearing phosphonic acid groups at the precise position. For this purpose, controlled radical polymerization of styrene phosphonate was carried out, where the substitution positions were varied based on ortho, metal, para directing groups. It has been revealed that polymers tethered with phosphonic acid groups at meta and ortho positions display suppressed ion clustering behavior than those with para position acid group, attributed to the dominant hydrogen bonding interactions of neighboring acid groups. |
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L70.00144: Self-Assembled Shape-Anisotropic Diblock Copolymer Particles from Evaporative Emulsions: Experiment and Theory Kang Hee Ku, Young Jun Lee, YongJoo Kim, Bumjoon Kim We report the systematic design of shape-anisotropic diblock copolymer (dBCP) particles based on a new theoretical model that embodies entropic penalty associated with bending of the cylindrical and lamellar dBCP chains upon deformation of the particles. First, we produced the convex-lens shaped (oblate) and football-shaped (prolate) PS-b-PDMS particles, where the aspect ratios (AR) were tunable over a broad range from 1 to 10. Of note, the AR of oblate particle increased almost linearly up to 10 as the particle size increased, whereas the increase of AR for the prolate particle was limited to 2.0. To understand this discrepancy, we developed the theoretical model that includes the bulk elastic and bending energies of dBCP cylinders and lamellae, and the surface energy between the particle/ surrounding medium. For oblate particles, the high excessive bending energy of the curved cylinders at the periphery of particle can be released by increasing the AR of particle. However, the relatively low excessive bending energy of curved lamellae of prolate particles prevents the particles from having a high AR. |
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L70.00145: Coupling between mean curvature and texture in thin block copolymer film Gabriel Catalini, Aldo Daniel Pezzutti, Daniel Vega Using a phase field approach we study the orientational coupling between the pattern developed by a lamellae forming block copolymer thin film and a topographically patterned substrate. Utilizing the Brazovskii free energy functional for a conserved order parameter, we perform a Taylor series expansion on the film thickness to obtain an effective geometric potential that correlates the smectic texture orientation to the curvature of the underlying surface. The results of this expansion are in good agreement with numerical results obtained through a Cahn-Hilliard model and experimental data on curved monolayers of asymmetric diblock copolymers. |
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L70.00146: Modelling Silica in Aggregates of Block Copolymers Pallabi Haldar, Alessandro Patti, Flor R. Siperstein There is developing interest in the use of Periodic Porous Materials (PPMs) synthesized from silicic acid and amphiphilic block copolymers in drug delivery and catalysis. Existing studies of the formation of PPMs have not drawn a clear conclusion as to the formation mechanism. In the prior studies two formation mechanisms were suggested; Liquid Crystal Template (LCT), where silicic acid plays no active role in the formation, and Co-operative Mechanism, where silicic acid plays a role in the formation. |
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L70.00147: Thermally Induced Phase Transitions in Amorphous-Crystalline Brush Block Copolymers Gayathri Kopanati, Benjamin M Yavitt, Huafeng Fei, Ruipeng Li, Masafumi Fukuto, James J Watkins Temperature resolved small angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) were used to investigate the temperature dependent phase transitions of five lamellae forming poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) brush block copolymers. Asymmetric lamellar morphologies were observed for all the PS-b-PEO series irrespective of their volume fraction and backbone length. The temperature dependent SAXS and WAXS reveal the presence of long-range order up to 140 °C. Unlike their linear counterparts, the primary peak position (q*) and full-width half maximum (FWHM) of q* remain constant, indicaxting no order-disorder transition (ODT) up to 200 ° C. The melting and crystallization of the PEO side chains co-exists within the lamellar morphology. Isothermal crystallization studies were conducted to investigate the crystallization kinetics of the PEO domain. The results indicate a two-stage crystallization process with Avrami exponents of 1 and 2, suggesting a one-dimensional initial stage followed by two-dimensional growth at later times. |
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L70.00148: The Systematic Study of Porous Monoliths to Measure Diffusion Induced by Hydrochloric Acid Paola Lo-ez There is the open question of the effect of loaded and non-loaded hydrogels with CaCO3 on diffusion kinetics. Formulations of PEDGA solutions were created containing varying concentrations of CaCO3 since higher concentrations would result in the material to develop yield stresses. The formulation was polymerized into flat monolothis using UV light rays. The 200 µm monoliths were swelled in H2O for 24 hours. Then, were subjected to a diffusive dissolution experiment and submerged into different concentrations of HCl (1 M/L to 0.06 M/L) and CaCO3 (0% to 25%). Time measurements were taken assuming that the longer the hydrogel was soaked in HCl the less CaCO3 and the more porosity. Pictures taken with an SEM of the porous dissolution fronts measured over time show the diffusion reaction scheme fits a model of diffusion of the square root of time. Also, a pH sensitive dye experiment was carried out in the porous hydrogels. The methyl orange soaked hydrogels were put in an aqueous HCl bath, and the movement of the concentration front was measured assuming the dye is trapped and the reaction is limited by diffusion of the acidic front. Rearranging the diffusion equations, diffusion coefficients were retrieved for the reactions. |
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L70.00149: Effect of Partial Saturation on Thermodynamic Interactions in Polydiene/Polyolefin Blends Jialin Qiu, Megan L Robertson, Ramanan Krishnamoorti Polymer blends exhibit properties that are highly dependent on interactions between components, typically quantified by the Flory-Huggins interaction parameter, χ. Polyolefins and polydienes are important materials with commercial relevance in elastomer applications. The majority of previous studies on the thermodynamics in polyolefin and polydiene systems have focused on polymer pairs within the same class, which generally exhibit a small and weakly temperature dependent χ. There is little quantitative information on thermodynamic interactions of polydienes and polyolefins. In our previous work, we characterized the χ parameter in a model polydiene/polyolefin blend based on 1,2-polybutadiene (1,2-PBD) by small angle neutron scattering (SANS). We observed an unusually large χ parameter in blends of 1,2-PBD and saturated 1,2-PBD that exhibited a strong temperature dependence. We also studied the impact of partial saturation on χ of polydiene/polyolefin blends. The χ(T) behavior in blends of fully saturated 1,2-PBD with partially saturated 1,2-PBD, at varying levels of saturation, was characterized. The applicability of the random copolymer theory to predict χ(T) behavior in these blends was evaluated. |
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L70.00150: Temperature-induced coil-globule transition of polypropylene oxide in aqueous solutions Rasika Dahanayake, Udaya R Dahal, Elena Dormidontova Polypropylene oxide (PPO) is a biocompatible polymer which is used in a wide range of industrial to biomedicalapplications, e.g. as a component of the commercial family of Pluronics. Using all-atom molecular dynamics simulations with modified OPLS forcefield we study the conformational changes of PPO in aqueous solutions as a function of temperature. We analyzed the temperature induced change in the PPO radius of gyration and correlate it with the polymer hydration properties, such as hydrogen bonding, hydration number, solvent accessible surface area, etc. We found that the coil-globular transition is accompanied by a noticeable reduction in polymer-water hydrogen bonding. We also estimate the heat capacity change as a function of temperature, which exhibits a maximum at the transition point and compare it with experimental data. |
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L70.00151: Simulating Diblock Copolymer Micelles in Binary Explicit Solvents Jing Zong, Dong Meng Amphiphilic block copolymers form nanoscale assemblies when dissolved in a selective solvent. Such self-assembled structures have wide-ranging applications as drug delivery vehicles and nanoreactors, etc. A powerful method to manipulate the assemblies is to vary the composition of solvent mixtures. Unlike single solvent solution, computational studies of amphiphilic block copolymers in solvent mixtures are rarely reported due to high computational cost associated with the necessity of treating solvents explicitly. Here, the Field-Accelerated Monte Carlo [1] simulation is employed in the expanded grand canonical ensemble to study the micelle formation of diblock copolymers in binary solvents: one selective solvent and one good solvent for both blocks. We investigate effects of molecular weight and solvent composition on micelle morphology, critical micelle concentration, and micelle size and aggregation number. It is found that distribution of the good solvent is highly inhomogeneous, concentrating at micelle interface and partitioning unevenly outside/inside micelle cores. Solvent intake by micelle cores increases with polymer molecular weight, affecting the way micelle size and aggregation number change with solvent composition. |
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L70.00152: Local Structure and Relaxation Dynamics in the Brush of Polymer-Grafted Silica Nanoparticles Yuan Wei, Michael Hore Polymer chains are grafted to nanoparticle (NP) surfaces for a variety of purposes, including altering NP solubility or dispersion within a polymer matrix. At high grafting densities, high molecular weight polymers adopt two primary conformations on the NP surface. Polymer chains near the NP core are stretched in the concentrated polymer brush region (CPB). Farther away from the core, polymer chains are less confined and the conformation becomes more ideal in the semi-dilute polymer brush region (SDPB). Using a combination of small-angle neutron scattering (SANS) and neutron spin echo (NSE) spectroscopy, we directly characterized both the structure and dynamics of the CPB and SDPB on poly (methyl acrylate) (PMA) grafted SiO2 NPs by selectively deuterating each region separately. Analysis of SANS measurements using a new core-chain-chain (CCC) model confirmed that the portion of the polymer chains in the CPB region are stretched, and transitions to a more ideal conformation in the SDPB region. From NSE, we found the dynamics in the CPB region were found to be much slower than the SDPB region across all length scales, and followed the Zimm model. |
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L70.00153: Thermodynamics of Binary and Ternary Polymer Blend Nanocomposites Shawn Maguire, Nadia Krook, Patrice Rannou, Manuel Marechal, Kohji Ohno, Russell John Composto Polymer nanocomposites (PNC), which are a combination of organic and inorganic fillers and a polymer matrix, have found great scientific interest due to the fact that the material properties of the PNC are largely determined by the chemical composition of the polymer as well as the type of fillers. While the fundamental physics governing the phase space of polymer blends is mature, there is a significant lack of understanding of the thermodynamics and kinetics that govern PNCs. In this work, we investigate model binary and ternary nanocomposites of poly(methyl methacrylate) grafted silica nanoparticles (PMMA NP), poly(styrene-ran-acrylonitrile) (SAN), and poly(methyl methacrylate) as a platform to elucidate the governing thermodynamic contributions. The thermally annealed films were characterized using electron microscopy and x-ray scattering, revealing lower critical solution temperature (LCST) behavior in the binary composite and an increased miscibility window in off-critical compositions for the ternary. These results extend the current understanding of PNC phase behavior and allow for greater control over NP dispersions. |
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L70.00154: Vinyl Imidazole Sulfonate-based Zwitterionic Copolymers with Tuneable Adsorption on Carbonates Mohammed Kawelah, Mariam F. Alghamdi, S. Sherry Zhu, Ayrat Gizzatov, Yuan He, Timothy M Swager Polymer injection in hydrocarbon reservoirs has been of great interest in petroleum engineering as an enhanced oil recovery (EOR) method. Injection of aqueous solutions of polymers into reservoirs increases the fluid viscosity and reduces its relative permeability in the reservoir, and hence improves volumetric sweep efficiency for EOR applications. However, the flow of polymeric solutions in porous media is subject to some particular effects such as non-Newtonian flow, degradation (thermal, physical, bacterial, and chemical), retention and inaccessible pore volume that are key to evaluating the success of a polymeric flooding. Significant polymer adsorption on the rock surface under high salinity and high temperature reservoir conditions is one of the most major challenges in polymer flooding EOR. Here we report the dynamic adsorption studies of four brine-soluble zwitterionic copolymers containing vinyl imidazole sulfonate using a Quartz Crystal Microbalance and core flooding at high temperatures. Our results indicate that the dynamic adsorption of the polymers on carbonates correlates to their structure variation and fluid properties, and a small presence of certain functional co-monomers on the polymers dramatically changes their dynamic adsorption. |
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L70.00155: Nonmonotonic glass transition behavior of polystyrene film in contact with polystyrene brushes Wooseop Lee, Hoyeon Lee, Vaidyanathan Sethuraman, Du Yeol Ryu, Venkatraghavan Ganesan The interplay between a polymer melt the substrate grafted with ‘chemically identical’ polymer brushes has attracted attention due to the possible applicability to slip, adhesion, wettability, and lubrication. In this study, we controlled grafting density (σ) and chain length of polystyrene (PS) brushes on substrates to investigate their effect on the glass transition temperature (Tg) of overlaying PS films. To our surprise, we observed a nonmonotonic change of the Tg of PS film as a function of σ with the maximum value that exceeds the Tg of bulk PS. A computer simulation supports our experimental results in terms of the local segmental dynamics in overlaying PS film, which is related to the enhanced friction by interpenetration between the melt (PS film) and the grafted layer. |
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L70.00156: Ion-Conducting Polymers as Interfacial Layers in Solid Electrolytes Arvin Sookezian, Priyadarshini Mirmira, Shrayesh Patel, Stuart J Rowan The development of safe lithium/lithium ion batteries is of interest for large-scale energy storage applications such as electric vehicles. The use of solid-electrolytes (SE) is a promising alternative to commonly used liquid electrolyte based batteries, which have safety and electrochemical stability concerns. Notably, solid-state systems are bottlenecked in performance due to inadequate solid-to-solid contact between the SE and the electrode that leads to high interfacial impedance. To address this challenge, we have developed a class of ion-conducting polymers that can be utilized as thin interfacial layers that help mitigate the poor adhesion between the solid interface while still permitting lithium ion-transfer across the interface. We specifically report on the lithium-ion conductivity, mechanical, and adhesive properties of our materials. Lastly, we report the electrochemical stability and performance of the ion-conducting interfacial layers in normal lithium-ion battery operating conditions. |
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L70.00157: Brushes of Peptide Coiled Coil Bundle Chains Matthew Langenstein, Darrin Pochan Through solution self-assembly, computationally designed peptide coiled coil bundles (CCBs) have shown the ability to produce 2-D lattices, nanocages, nanotubes, and 1-D supramolecular polymers. However, to date no studies have been performed on the impact of substrate interactions on the structure of CCBs. Successful preservation of the coiled coil motif during surface conjugation could provide a robust pathway towards the computational design of stimuli-responsive latticed self-assembled monolayers and serve as a template for layer by layer growth of complex brushes with exact sequence control. In this poster the use of atomic force microscopy (AFM), angle resolved X-ray photoelectron spectroscopy (ARXPS), and quartz crystal microgravimetry (QCM) to characterize peptide layer thickness, surface topography, orientation, and deposition rate will be discussed. Additionally, the impact of temperature, solvent, and pH on the structure of cysteine terminated CCBs on planar gold substrates will be examined. |
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L70.00158: Impact of casting conditions on mechanical properties of polynorbornene membranes under typical biobutanol operating conditions. Meeta Trivedi, Bryan Vogt Poly(butylnorbornene)-ran-poly(hydroxyhexafluoroisopropyl norbornene) (BuNB-r-HFANB) is a promising material for biobutanol membranes with Tg’s for both segments exceeding 300oC to provide the potential for highly stable membranes. During operation, the BuNB-r-HFANB is swollen by the aqueous butanol in the broth that impacts its properties. The membrane performance is dependent on how it is cast. Here we investigated effect of four different casting solvents (THF, Toluene, DMF and Butanol) on the mechanical properties of these membranes using DMA. The change in mechanical properties in the butanol broth was enabled by using a submersion cell with DMA. The effect of temperature in both the dry and swollen state was also examined to provide insights into how the mechanical properties of these membranes would be expected to change during operation. |
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L70.00159: Biocellulose Nanofibrilar Adhesives with Antigen-Antibody Interactions for Dermal Therapy Seulgi Kim, Ji Eun Kim, Jeong Yi Kang, Jin Woong Kim Biocellulose nanofibers (BCNFs), known as bacteria-derived celluloses, are attractive biomaterials, since they are biocompatible and can be easily chemically modified for a variety of biomedical treatments. When primary hydroxyl groups on the BCNFs are substituted to carboxylic groups by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation, they are able to physicochemically interact with biomolecules. Herein, we propose a new BCNF-based bioadhesion system for dermal therapy. The essence of our approach is that the antibody-conjugated BCNFs are bound to involucrin in the corneocyte of stratum corneum. The BCNF bioadhesives were fabricated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysulfosuccinimide (sulfo-NHS) coupling reaction of antibody. Then, the adhesion force between the antibody-conjugated BCNFs and porcine skin was characterized by using the axial rheometer measurement. Finally, we demonstrated that our BCNF bioadhesives exhibited such a strong interaction with the skin tissue even under wet conditions, thus promising a variety of biological applications in the field of dermal therapy. |
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L70.00160: Oligomeric Cellulose Co-Crystallization with DMSO Xin Zhang, Feng Jiang, Yimin Mao, Doug Henderson, Yoshiharu Nishiyama, Robert M Briber, Howard Wang Oligomeric cellulose with a median degree of polymerization of 7 (DP7) is produced by hydrolysis of cellulose in phosphoric acid. DP7 molecular weight distribution was characterized by NMR, MALDI-TOF, and GPC. DP7 is soluble in hot DMSO and crystallizes in the form of spherulites upon cooling. The spherulite morphologies and crystallization kinetics was characterized by polarized optical microscopy. The structure of the crystal has been studied by synchrotron radiation XRD, TEM and MD simulation. The oligomeric cellulose and DMSO co-crystallize. After removing excessive solvent, the crystal is metastable in dry air but transforms into the cellulose II crystal structure when exposed to humidity. |
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L70.00161: Synthesis and Self-Assembly of Oligomeric Cellulose-block-Poly(ethylene glycol) Diblock Copolymers Feng Jiang, Xin Zhang, Doug Henderson, Wonseok Hwang, Howard Wang, Robert M Briber Block copolymers containing cellulose have not been well studied or understood partly due to the poor solubility of cellulose in common solvents. In this study, well-defined oligomeric cellulose-block-poly(ethylene glycol) diblock copolymers, Cell1.1k-b-PEG1.7k (Mn = 2.8 kD, PDI = 1.04) and Cell1.1k-b-PEG5k (Mn = 6.1 kD, PDI = 1.02), have been synthesized via coupling reactions. The volume fractions of oligomeric cellulose in Cell1.1k-b-PEG1.7k and Cell1.1k-b-PEG5k diblock copolymers are 0.32 and 0.14, respectively. Due to the incompatibility between the cellulose and PEG, Cell-b-PEG diblock copolymers can separate at a local scale forming cellulose-rich and PEG-rich nano-domains, which further organize into larger scale structures, both in solutions and in the bulk. Small-angle X-ray scattering, atom force microscopy, and electron microscopy show hierarchical structures of Cell-b-PEG from nanometers to microns. |
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L70.00162: SOFT CONDENSED MATTER
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L70.00163: New coarse grained model for the study of the dynamics of the Worm Like Chain Angelo Setaro Semiflexible polymers display rich and varied behavior, distinct from both their rigid and flexible counterparts. This diversity arises from the interplay between bending energetics and conformational entropy. This energetic balance manifests as correlations between orientations along the polymer backbone, which depend on the flexibility of the polymer. Typically, the Kratky-Porod model is used to study semiflexible polymer systems, however, it is of limited utility when attempting to study non-equilibrium polymer dynamics, particularly over long timescales in flow. Currently, coarse grained models exist which allow for the study of polymers over longer time scales than the Kratky-Porod model, but at the cost of much fine grained information. To address this deficiency and bridge the gap between models, we propose a new coarse grained model for semiflexible polymers that reproduces some key behaviors of the Kratky-Porod model while simultaneously allowing for study of polymeric systems on a longer time scale. In this work, we have used Brownian dynamics to quantify and assess the accuracy of other key features of the model. |
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L70.00164: Dynamic and Structural Critical-like Behaviors in glassy monolayers of colloidal ellipsoids Zhongyu Zheng, Yilong Han Whether the glass transition is a purely dynamic transition or a thermodynamic one is a long-standing debate in condensed matter physics. Critical behaviors have been found in translational degree of freedom in glasses composed of spheres with local polycrystalline structures, but it is not clear if criticality exists in more general glassy systems without crystalline orders or composed of non-spherical particles. Here, we show rich critical behaviors in both translation and rotation in monolayers of monodispersed colloidal ellipsoids lacking crystal-like structures. We found an Ising criticality at the ideal glass transition point φ0 for the static glassy structures, local structural entropies and dynamic slow-moving clusters. These structural and dynamic quantities sharing the same Ising criticality are a direct evidence of the critical phenomenon and thermodynamic nature of the glass transition at φ0. A different criticality is found at the mode-coupling point φC for the fast-moving clusters reflecting a dynamic glass transition. These results may explain the theoretical puzzles that the dynamic correlation length diverges at two different temperatures and the relaxation mechanism changes around TC. |
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L70.00165: Measure particle diffusion in cytoskeletal networks with light-sheet and differential dynamic microscopy Christelle Matsuda, Sylas Anderson, Rae Robertson-Anderson, Ryan J. McGorty Filamentous actin and microtubules contribute to the crowded environment of the cytoplasm. Modeling the cytoplasm, we create networks of varying crosslinking motifs and varying ratios of actin and microtubules. We crosslink either actin to actin, tubulin to tubulin, or tubulin to actin. We add micron-sized fluorescent beads to the various networks, record videos of the samples using light-sheet microscopy, and perform differential dynamic microscopy (DDM) analysis. We compare DDM and single-particle tracking results to examine differences between ensemble and single-particle transport properties. We find varying degrees of anomalous diffusion and significant heterogeneity in the dynamics, particularly in actin environments. |
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L70.00166: Particle-tracking reveals heterogeneous subdiffusion in in vitro cytoskeleton composites Sylas Anderson, Christelle Matsuda, Ryan J. McGorty, Rae Robertson-Anderson The diffusion of microscopic particles through the cell, important to processes such as transcription, viral infection, transfection and gene delivery, is largely controlled by the complex cytoskeletal network that pervades the cytoplasm. The cytoskeleton is predominantly made up of thin semiflexible actin filaments and thicker, more rigid microtubules, as well as binding proteins that can crosslink each filament. By varying the relative concentrations of actin and microtubules, as well as the degree to which each filament is crosslinked, the cytoskeleton can display a host of different structural and dynamic properties that in turn impact the diffusion of particles through the network. Here we use single particle tracking methods to quantify the mean-squared displacements of microspheres diffusing in custom-designed in vitro composites of actin and microtubules. We show that particles exhibit subdiffusion, with scaling exponents and transport coefficients that decrease as the relative fraction of actin in composites increases. By evaluating the distributions of bead displacements, we also find that composites induce unique non-gaussian diffusion characteristics and substantial heterogeneities in particle trajectories. |
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L70.00167: Colloidal diffusion and viscoelasticity in blended solutions of supercoiled, ring and linear DNA Megan Lee, Karthik Reddy Peddireddy, Sylas Anderson, Rae Robertson-Anderson DNA, which has been widely studied as a model polymer system, naturally exists in different topological forms including linear, relaxed circular (ring) and supercoiled. While the reptation model can be used to understand molecular transport and interactions in systems of entangled linear polymers, it is far less successful in describing the dynamics of entangled supercoiled or ring polymers. The properties of entangled polymer blends of different topologies and polymer solutions near the critical entanglement concentration are also still poorly understood. Here, we address these problems by creating blended solutions of (1) entangled linear and ring DNA of varying blend ratios and (2) supercoiled and ring DNA of varying overall concentrations from the semidilute to entangled regime. We use particle-tracking methods to measure the diffusion of colloids embedded in these solutions as well as the corresponding linear viscoelastic properties. We reveal previously unobserved and unpredicted dependences of transport and viscoelasticity on the ratio of linear to ring DNA in blends as well as the overall solution concentration. |
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L70.00168: Tuning dynamics of moisture responsive wrinkling surfaces Songshan Zeng, Rui Li, Dianyun Zhang, Luyi Sun The wrinkle dynamics (such as reversibility and stability) of human skin are affected by the external stimuli, as well as the skin’s structure and mechanical properties. Inspired by these tunable responses, three types of moistureresponsive wrinkle dynamics are achieved, for the first time, through a single film–substrate system. These dynamics include: (1) completely reversible wrinkles formation; (2) irreversible wrinkles formation I: the initially formed wrinkles can be permanently erased and never reappear; and (3) irreversible wrinkles formation II: once the wrinkles form, they can no longer be erased. The key to success is to control the stiffness and thickness ratios of the film and the substrate, and tailor the crosslink degree/gradient of the film to allow for moisture-dependent changes of modulus and swelling degree. These unique responsive dynamics motivate the invention of a series of optical devices triggered by moisture, including anticounterfeit tabs, encryption devices, water indicators, light diffusors, and antiglare films. This study also paves the road for further understanding of the skin wrinkling dynamics and manipulation. |
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L70.00169: How crosslinking actin filaments influences the microscale viscoelastic properties of actin-microtubule composites Madison Francis, Rae Robertson-Anderson, Shea Ricketts, Jennifer Ross The strength and mobility of cells is dependent upon the interactions between two protein filaments that comprise the cytoskeleton: actin and microtubules. These proteins form entangled networks that can also be chemically crosslinked to enable a wide range of mechanical properties. Here, we use optical tweezers microrheology to determine how varying concentrations of actin crosslinkers influences the viscoelastic properties of actin-microtubule composites. We create equimolar co-entangled networks of actin and microtubules with varying concentrations of actin crosslinkers. We use optical tweezers to apply both oscillatory and constant speed microscale strains over a range of rates and distances while simultaneously measuring the force the networks exert to resist these strains. We quantify the frequency-dependent complex viscosity, the nonlinear stress response, and the relaxation dynamics following strain. Surprisingly, we find that increasing the concentration of crosslinkers yields a decrease in network elasticity and stiffness. |
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L70.00170: Mechanism of reinforcement in soft composites: random fiber networks with inclusions Mohammad Islam, Catalin Picu The mechanical behavior of athermal random fiber networks embedding particulate inclusions is studied in this work. Composites in which the filler size is comparable with the mean segment length of the network are considered. In presence of inclusions, the small strain modulus increases, while the ability of the network to strain stiffen decreases relative to the unfilled network case. The reinforcement induced by fillers is most pronounced in sparse networks of floppier filaments that deform in the bending-dominated mode in the unfilled state. As the unfilled network density or the bending stiffness of fibers increase, the effect of filling diminishes rapidly. Fillers lead to a transition from the soft, bending-dominated, to the stiffer, axial-dominated, deformation mode of the network, transition which is primarily responsible for the observed overall reinforcement. These results provide a justification for the broadly observed difference in reinforcement in sparsely versus densely cross-linked networks at given filling fraction, and provide guidance for the further development of network-based materials. |
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L70.00171: Characterization of Aqueous Hyaluronate Solutions using Static and Quasielastic Light Scattering David Walls, Laurel Hunter, Vingnesh Venkataramani, David Ross, Scott Franklin, Moumita Das, George Thurston Human vitreous humor contains a hydrogel made up of a network |
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L70.00172: Nonlinear mechanics of composite fiber networks Sadjad Arzash, Jordan Shivers, Fred C. MacKintosh Fibrous networks such as collagen are ubiquitous in biological systems. Although the mechanical behavior of single fiber networks has been, both experimentally and theoretically, well studied, understanding the effect of the interplay between different biopolymer networks remains unclear especially under large deformations. In this work, we model a rigid fiber network inside a soft and flexible underlying matrix. This double network model enables us to study the effect of internal interactions of different networks on their overall mechanics. We find that the linear shear modulus of the composite system is greater than the sum of the individual linear shear moduli. Moreover, by calculating the non-affine fluctuations, we see clear suppression of fluctuations in the rigid fiber network. We also find a mechanical phase transition between matrix-dominated and fiber-dominated states. |
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L70.00173: Classification and prediction of the mesophases of block copolymers Sadato Yamanaka, Takeshi Aoyagi Self-organization and the resultant mesoscopic structures in block copolymer systems are of great advantage to applications such as nanolithography. Nevertheless, the whole phase behaviors still have not understood well even in ABC triblock copolymers. We study on classification problem on the classical phase diagram of AB diblock copolymers by means of supervised machine learning. We compare three model: kernel support vector machine (SVM), random forest, and k-nearest neighbor method. The prediction accuracy of kernel SVM is 94.5%, which is higher than the other two methods. This indicates that kernel SVM can be a candidate of classification model that is applicable to more complex architectures, such as linear/star ABC triblock copolymers. |
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L70.00174: Using an autoencoder to reduce experimental noise Nancy Thomas, Jordan Hoffmann, Lisa Lee, Parker LaMascus, Shmuel Rubinstein, Christopher Rycroft Experimental noise is ubiquitous in the sciences. Some of this noise is random, however some is systematic. We use machine learning to try to remove the systematic noise in experimentally found scans of crumpled sheets of paper in order to be able to study this classical disordered system. Properties that were previously uncovered using other denoising mechanisms were that crease mileage is a state variable of crumpling, is independent of crumpling history, and has a logarithmic scaling property. Through the use of an autoencoder, we were able to recover the scaling properties of crease mileage while improving the automation of the denoising process. This denoiser is able to outperform other methods on extremely noisey sheets. The removal of noise from our data is essential in order to be able to further explore the characteristics of the crease networks in a crumpled sheet. |
(Author Not Attending)
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L70.00175: Probing mechanical properties of particle shells formed on droplets by electric field-induced wrinkling Alexander Mikkelsen, Zbigniew Rozynek Fabricating curved monolayers that mimic the properties from natural shells can help researchers to develop lighter, stronger and more flexible materials, better drug delivery and encapsulation systems, etc. Here we investigate synthetically made particle shells formed on droplets in a bulk fluid, in context of their mechanical properties. We used induced compressive stress on the particle shells by applying electric fields. In response to the stress, the particle monolayers folded and formed wrinkles with characteristic wavelengths. By deriving a simple model for particle shell wrinkling, we used these wavelengths to estimate the Young modulus and bending stiffness of the shells. Our results indicate that the elasticity of particle shells decreases with particle and shell size. We also show that deformation cycles induced by electric fields can be used to increase particle packing of monolayers on droplets and reduce wrinkle formation. These results suggest that in addition to probing mechanical properties, our approach can also be used to tailor the surface properties of shells, i.e. their permeability and roughness. |
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L70.00176: Emergent Dynamics of Paramagnetic Suspensions under Toggled Magnetic Fields Hojin Kim, Eric M Furst Suspensions of superparamagnetic colloidal particles are subjected to toggled magnetic fields by switching on and off the field repeatedly. At sufficiently high field strengths, the microstructure of the suspension begins in a solid, gel-like state and anneals to droplet-like domains governed by time-averaged bulk and surface energies. Here, we study the effect of the toggled-field duty cycle. At frequencies range investigated in this study (0.33-5Hz) and high duty cycle ratio (0.8), the suspensions form column-like microstructures that do not evolve into energetically favorable states. In this case, the period the field is off is shorter than the particle characteristic diffusion time scale. As duty cycle decreases, however, microstructures grow to ellipsoidal-shape as a result of the sufficient time for particle diffusion. Under a small range of conditions (1.5-3.5 Hz, 0.2 duty cycle ratio), we observe a new class of wavy-shaped microstructures with dynamics that exhibit a strong and continuous process of rotation, coalescence, and breakup. We attempt to understand these dynamics by considering the hydrodynamic forces exerted by a collection of thermal ratchets composed of particles in an asymmetric process of ballistic approach and diffusive relaxation. |
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L70.00177: ABSTRACT WITHDRAWN
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L70.00178: ABSTRACT WITHDRAWN
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L70.00179: Quantifying the surface tension of non-equilibrium colloidal fluids Caroline Riedstra, Jing Wang, Ryan J. McGorty Through the use of a colloid-polymer system employing temperature-sensitive pNIPAM microgel colloidal particles, we observe the nucleation and dissolution of colloid-rich liquid droplets. We use light-sheet microscopy to observe the formation and dissolution of colloid-rich droplets in three-dimensions and with optical sectioning. Our colloid-polymer system allows us to precisely tune the equilibrium state--mixed or demixed--by adjusting the sample temperature. With videos obtained from the light-sheet microscope, we perform image analysis of fluctuating droplets to extract the surface tension. |
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L70.00180: Probing viscoelasticity of dilatant fluid by solid projectile impact Kazuya Egawa, Hiroaki Katsuragi Dilatant fluids offer complex rheological properties such as discontinuous shear thickening (DST). In recent years, various solid-impact experiments onto a dilatant fluid have been performed to reveal the physical properties of DST. Interesting phenomena such as dynamic jamming [S. R. Waitukaitis & H. M. Jaeger,Nature 487, 205(2012)] and dynamic fracturing[M. Roche et al., Phys. Rev. Lett. 110 148304(2013)] have been reported in previous reserches. In addition, peculiar surface deformation of the vibrated dilatant fluid has also been found[F. S. Merkt et al., Phys. Rev. Lett. 92 184501(2004)]. In this study, we perform a simple solid-projectile impact to a dilatant-fluid target to observe the penetration and rebound dynamics. In addition, to investigate the effect of vibration to the rheological properties of dilatant fluid, mechanical vibration is also applied to the dilatant fluid. From these results, the rebound timescale and restitution coefficient are measured. To characterize the viscoelasticity, we assume a simple attenuating-oscillation model. Using the model, the effects of impact inertia, boundary conditions, and mechanical vibration to the rheological properties are systematically studied. |
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L70.00181: Cratering and collapse of an inclined granular layer by oblipue impact of a spherical projectile Shinta Takizawa, Ryusei Yamaguchi, Hiroaki Katsuragi The oblique impact of a solid sphere onto an inclined granular layer is experimentally studied. The inclination angle of the target granular layer is varied from 0 to 33 degrees. The incident angle is also varied from 10 to 170 degrees. The range of impact velocity is 10 - 100 m/s. As a result, we observe following behaviors. When the incident angle is 90±10 degrees (almost normal impact), simple penetration of the projectile is observed. However, rebound or ricochet of the projectile occurs when the incident angle is smaller than 70 degrees (or larger than 110 degrees). When the target granular layer is steep enough, the transient crater produced by the impact is significantly modified by the asymmetric collapse of crater wall. Due to these complex effects, the final crater shape becomes complex. In this study, the characteristic dimensions of the crater (diameter, depth, and cavity volume) are measured and scaled by the effective impact kinetic energy transferred to the target by the projectile impact. While the crater volume can be scaled with a universal exponent, the specific volume value depends on the inclination angle. |
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L70.00182: Granular flow dynamics in a vibrating system from multiple points of view: Laboratory experiments, continuum modeling, and numerical simulations Daisuke Tsuji, Michio Otsuki, Hiroaki Katsuragi This study investigates granular flow dynamics in a vibrating system from multiple directions: laboratory experiments, continuum modeling, and numerical simulations. In the experiment, a conical granular pile is subjected to vertical vibration. Depending on its strength, granular particles are fluidized, and the shape of the pile is gradually relaxed. During the vibration, the relaxing pile is observed by a high-speed laser profiler. Based on those data, we have proposed a continuum model, which can predict how the flux of granular particles is determined. This model has only one fitting parameter that indicates the conversion efficiency from inputted vibration energy into granular transport energy. By comparing the experimental data obtained under various conditions, this parameter turned out to be a universal constant. In order to consolidate this universality and explore the flow property inside the pile, a series of particle-scale numerical simulations have also been conducted. As a result, we have confirmed that the continuum model is satisfied and the conversion efficiency does not change in numerical simulations. We have also found that the velocity decreases exponentially from the surface of a pile, which suggests the presence of shear-band structure. |
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L70.00183: Reversible Sol-Gel Transition of Silicone Complex Oils Using Hydrophobically Modified Attractive Hectorite Nanoplatelets as Rheology Modifiers Doyeon Kim, Daehwan Park, Yeong Sik Cho, Jin Woong Kim Hectorite nanoplatelets (HNPs) have truly intriguing surface properties such as high specific surface area, high cation exchange capacity. Herein, we introduce a facile but robust approach to fabricate attractive hectorite nanoplatelets (AHNPs), in which the surface of HNPs was hydrophobically modified by using a cationic surfactant, dimethyl dioctadecyl ammonium chloride. We could finely disperse the AHNPs in the silicone oil by repeated high pressurized homogenization. The suspension rheological studies revealed that the AHNPs interacted to form a strong gel phase that exhibits the reversible shear stress-responsive sol-gel transition. Based on the chemical and structural characterization of AHNPs by using XRD, FT-IR, AFM, and TEM analyses, we interpreted this is attributed to the weak but long-range edge-to-edge interaction of AHNPs in the silicone oil, which is induced by the hydrogen bonding between small amounts of hydroxy groups at the edge of AHNPs. The AHNPs fabricated in this study are expected to be widely used as rheology modifiers for various oil-based complex fluids. |
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L70.00184: Using Pressure Sensors To Characterize Avalanche Dynamics On A Conical Bead Pile Katie Shideler, Susan Lehman A system of pressure sensors is used to characterize the dynamics of avalanches as they occur on a conical bead pile. The bead pile is a slowly driven critical system of roughly 20,000 steel beads, 3 mm in diameter, atop a circular base. We slowly drive the pile by dropping one bead at a time on the pile apex, and we record avalanches (the change in mass as beads leave the pile) occurring over the course of 60,000 bead drops. To complement this statistical information about the avalanche size probability distribution, we recently modified the base of the pile to add a system of eight pressure sensors that are monitored continuously during the data run. The sensors respond to shifting of forces within the pile during the avalanche, providing a way for us to characterize the types of bead motions occurring on the pile at different places on the pile and at different stages of the avalanche. With these sensors, we can characterize surface motion of beads on the pile independently from motion of beads off the pile. We are developing analysis techniques to characterize avalanches not just by the number of beads involved but also by the area of the pile participating in the avalanche; we propose an experimental definition for a system-spanning avalanche. |
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L70.00185: Controlling Interactions in Active Matter Systems Joshua Steimel, Sage Moreland, Alfredo Alexander-Katz It has been demonstrated in a 2D colloidal monolayer composed of active spinning ferromagnetic and passive colloids that an ultra-long range attractive interaction emerges between active colloids. This interaction was induced by the activity of the spinning particles and mediated by the elasticity of the passive colloidal monolayer. We demonstrate through experiments and simulations that the range and dynamics of this emergent attractive interaction can be tuned or reversed by changing the mode of activity or the composition of the passive monolayer. With a 3D Helmholtz-coil like apparatus we can change the mode of activity from spinning to a top-like motion. These tops exhibit a similar attractive interaction at long-range, however they repel at distances less than four particle diameters, unlike the spinners. The tops also effectively anneal the passive monolayer into almost perfect crystal grains while the tops occupy sites on the grain boundaries effectively functioning as dislocation sources. Additionally, by doping the passive colloidal monolayer with small concentrations of passive particles of different sizes the monolayer behaves more elastically. This increases the range of the interaction but the dopants impede dislocation motion so the rate of attraction decreases. |
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L70.00186: A Method to Measure Drag Coefficient of An Active Particle Chong Shen, H Daniel Ou-Yang The drag coefficient of an active particle is important because it reveals the energy cost of swimming of an active particle, i.e, micro-organisms or swimming colloids. We introduce a method to obtain the drag coefficient for an active particle by separately measuring diffusion and sedimentation. We test this method on an active Brownian particle (ABP) that is driven by induced-charge electrophoresis of Janus particles. |
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L70.00187: Macro and Micro Phase Separation in Mixtures of Active and Passive Particles Ryan Tollefsen, Jonathan Lu, Joshua Steimel, Alfredo Alexander-Katz Active spinning particles have been shown to phase separate when mixed with inactive particles. Here we present our work on controlling such phase separation to obtain microphase separation apart from the typical macrophase separation as a function of the reversal of the torque on the particles. Using this technique we can achieve control over the domain size as a function of the activity. We further show that the systems displays hysteresis as one changes the driving force. These results extend our knowledge of phase separation in mixtures of active and passive particles. |
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L70.00188: Snapping induced by controlled drying of polymer gels: from moving bonito flakes to jumping shells Yongjin Kim, Jay van den Berg, Alfred Crosby Dynamic changes in swelling states can induce life-like motions in bonito flakes placed on a hot Okonomiyaki. The shape transitions of these thin polypeptides films not only happen smoothly but also occur abruptly. Inspired by these generally occurring, but random events, we developed novel design principles for inducing self-repeating snapping motions during the drying process of swollen polymer disks that can persist until the depletion of the solvent. We demonstrate the ability to tune the system performance of these polymer devices to achieve either higher jumping kinetics (t ~ 2ms, Power ~ 370W/kg) or greater total energy output (Eout ~ 2J/kg) by controlling the geometry and boundary conditions. The performance of the snapping shells under different conditions was modeled with finite element analysis results. The systematic study on the snapping mechanism and its incorporation into engineered systems will bring great advantages for designing micro-scale, high-efficiency robots. |
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L70.00189: Temperature-invertible gel for manipulation of colloidal particles Cathy Zhang, Ya Liu, Cindy Wang, Xiaoguang Wang, Stefan Kolle, Anna Christina Balazs, Joanna Aizenberg We develop an actuatable, responsive gel surface with a set of periodically spaced, temperature-invertible ridges and demonstrate that this surface enables us to create large, dynamic arrays of a range of colloidal particles through multiple physical mechanisms. The surface is constructed from a responsive gel that is spatially patterned on a topographically ridged surface to form gel ridges that collapse to form valleys. Using both experiments and numerical simulations, we show that we can obtain fine-grained control over the amplitude of surface topography, where the exact trajectory of the surface change depends on the rate and direction of temperature change. We then sediment particles on the surface and quantitatively demonstrate how the dynamic features of this gel enable us to pattern colloidal assembly and release under low Reynolds number shear flow. Finally, we introduce biological particles on the surface and show how such a multifunctional surface provides opportunities in creating antifouling surfaces whose properties can be tuned on demand. |
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L70.00190: Competition and Cooperation among Chemically Active Sheets and Particles Abhrajit Laskar, Oleg Shklyaev, Anna Christina Balazs Using theory and simulation, we model the interactions among different, chemically active objects in a fluid-filled microchamber to establish conditions that drive these synthetic objects to display biomimetic competitive or cooperative behavior. The first objects are catalyst-coated, flexible sheets that generate buoyancy-driven fluid flows. The second objects are mobile tracer particles that move via diffusiophoresis towards higher reactant concentrations. We vary the sheets’ size and areal concentration of catalyst to tune the rate of reaction at this layer. Through these studies, we determine regions in phase space that lead to “aggressive” competition or “beneficial” cooperation within this dynamic, non-equilibrium system. As an example of competition, we show that when a low concentration of reactants is introduced into the solution, the larger sheet “catches” more tracers than a smaller sheet with a higher areal concentration of catalyst. Furthermore, we isolate conditions where single sheets acting alone do not capture tracers, but can trap the motile particles through cooperative interactions. These studies illustrate how purely physicochemical factors can promote behavior highly reminiscent of biological systems among active objects in fluidic environments. |
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L70.00191: Self-propelled Nanoparticles Johannes Sachs, Peer Fischer Chemically active particles that self-propel due to catalytic reactions have been demonstrated at various length scales. It has, however, not yet been experimentally established how the propulsion of very small chemical motors scales with size. For this reason, we use a unique physical nanofabrication technique, based on physical vapor deposition, to grow catalytically-active Janus particles. These can be grown at defined lengths ranging from 20nm to 500nm, and can contain photocatalytic materials. This allows us to switch the particle between its passive and active state and thereby potentially from Brownian to enhanced diffusion. The observation of the particles’ motion is, however, far from trivial. We report our latest experimental results from a variety of analytical techniques, some of which can be used in situ. |
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L70.00192: Seal Zone Mechanics: Mechanical Stability of the Endograft/Aorta Interface Luka Pocivavsek, Enrique Cerda, Christopher Skelly, Ross Milner Endovascular surgery (EVAR) has nearly replaced open aortic aneurysm repair. The long-term stability of EVAR repairs has come into question especially concerning graft endoleaks. Adhesion between the endograft and aortic wall is poorly understood and differs substantially from the traditional approach of kinematic fastening (suturing) utilized in open reconstructions. We provide a first general computational and theoretical approach to characterize and study seal zone mechanics. Our analysis (computational and analytical) shows that in the limit of no adhesion (or very weak adhesion) the endograft is always unstable relative to its position in the non-aneurysmal aorta. The energy driving graft displacement is the stored elastic energy in the aortic wall that comes from the oversizing of the stent graft. Adhesion between the aorta and endograft balances this stored elastic energy. This balance of adhesive energy to elastic energy is the central control parameter in the stability of the endograft. We develop a toy model for graft stability and apply it to patient specific geometries. Our work provides the first steps towards a robust physical understanding of the mechanics involved in EVAR stability that will allow for more durable future devices. |
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L70.00193: Controlling the strength of network materials: insights into failure mechanisms of random soft networks and composites Sai S Deogekar, Mohammad Islam, Catalin Picu Fiber networks occur abundantly at all length scales in biological and artificial materials. In most cases, the network has structural role and hence its failure defines the strength of the material. Since these materials are structurally stochastic, heterogeneity plays a major role in determining the dominant failure mechanism. In this work we establish relationships between network strength and various parameters defining the network structure and properties of fibers and bonds [1]. These provide guidelines for network design. Further, we explore the role of heterogeneity in defining the strength and consider structures in which the fluctuations in the mechanical fields are controlled by adjusting various network parameters. Specifically, we consider networks with rigid inclusions (composite networks) and networks with stochastic structural perturbations of increasing amplitude. The results are discussed against insights related to stochastic continua, from the literature. |
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L70.00194: In Situ TEM Imaging of Nanoscale Bubble Collapse and the Resulting Damage in Soft Matter Garth Egan, Xavier Lepro Chavez, Edmond Lau, Eric R Schwegler In recent years, it has been suggested that micron and sub-micron scale cavitation can occur in the human brain during explosive pressure wave, blunt trauma, or sports collision type events and that the resulting bubble collapse could be the main cause of damage leading to traumatic brain injuries. However, the behavior of sub-micron bubbles and their damgae potential to soft mater is not yet well understood. This is in part a result of the challenges associated with imaging on the necessary length and time scales. Here, we present the direct imaging of bubble collapse in a liquid cell using the Movie-Mode Dynamic Transmission Electron Microscope (MM-DTEM) at Lawrence Livermore National Laboratory. Bubbles were induced in ~1-3 µm of water using laser heating of 60 nm gold particles and typically found to collapse within 200 ns. Various polymers coated on the liquid cell substrates served as witnesses to potential damage. The experiments were performed in conjuncture with molecular dynamic (MD) simulations to further explore the dynamics of the system. |
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L70.00195: Characterization of Novel Surfactant Molecules for Liquid Crystal Phase Triggering Linda Oster, Benjamin Strain, Jessica Sleator, Jake Shechter, FNU Manisha, Sankaran Thayumanavan, Jennifer Ross Liquid crystal systems have the potential to produce macroscopic reactions from microscopic stimuli, making them exciting systems for triggered assemblies. Such triggerable systems are a cornerstone of biological systems’ ability to respond to their environment. Here, we use a novel surfactant composed of a trimer of amphiphilic molecules. These trimeric surfactants have three hydrophobic tails, with one tail varying in length. We have characterized the phase of the liquid crystal, 5CB, in spherical droplets as a function of surfactant type, surfactant concentration, and the diameter of the 5CB droplet. We find that small droplets, less than 11 µm in diameter, with high surfactant concentration, are more likely to be in the radial phase. We also find that the concentration and droplet sizes for the phase transition depended on the variable tail length. |
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L70.00196: A Generalized Interfacial Structure Analysis Model for the Crystal Morphology: β HMX JunBeom Cho, Won Bo Lee We studied the spiral growth mechanism of β-cyclotetramethylenetetranitramine (β-HMX) crystals with (0 2 0), (0 1 1), (1 1 0), and (1 0 1) faces, both experimentally and theoretically. In this work, a generalized interfacial structure analysis model is suggested to elucidate the morphology of β-HMX. There are two significant factors on crystallization procedure; 1) Molecular concentration near the surface of crystal 2) Whether pre-ordering of growth units occur during adsorption on the surface of each crystal faces. We investigated these through the Molecular Dynamic approach and metadynamics simulation, respectively. However, due to high conformational free energy barrier, pre-ordering of the growth unit does not occur and the factor 1 plays critical role in crystal growth, so the result of present work indicates that anisotropic local concentration of the growth units at the interface is the main factor determining relative growth rates, which was consistent with those of previous studies. |
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L70.00197: Computer simulations of associating liquid crystals Dimitri Baptiste, Elena Dormidontova Liquid crystals possess a range of interesting properties and are actively used in various technological applications. Reversible association, such as hydrogen bonding or metal-ligand complexation can provide additional mechanisms to control their properties leading to new applications including responsive functional materials. We employ Monte Carlo simulations using a spherocylinder model to predict the phase diagram for formation of the different ordered liquid crystalline phases in the presence of reversible associations. In particular we investigate the inter-relation between the strength of reversible association and the aspect ratio of liquid crystalline mesogens. The effect of confinement on system behavior will be discussed we well. |
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L70.00198: Static and Dynamic properties of self-assembled hybrid wormlike surfactant micelles: Molecular Dynamics Study HARI SHARMA, Elena Dormidontova Self-assembled wormlike surfactant aggregates have attracted considerable interest in both fundamental research and in practical applications due to their rich viscoelastic behavior and dynamic responsiveness to external conditions. Incorporation of polymer within wormlike micelles is shown to have enhanced stability and potentially superior viscoelastic properties. Co-assembly of polymers with surfactants in hybrid micelles is studied using coarse grained MD simulation with MARTINI force field and by united atom MD simulation with GROMOS53a6 force field. Simulations are carried out using GPU accelerated version of GROMACS 4.6.5. The change in micelle properties due to the presence of polymer is analyzed and the results are compared with available experimental data |
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L70.00199: Simulating the Response of Liquid Crystalline Elastomer Microposts to Light James Waters, Joanna Aizenberg, Anna Christina Balazs Liquid crystalline elastomers (LCEs) represent a realizable physical system that can exhibit a large, non-linear response to an environmental stimulus. By adding light-sensitive moieties to the mesogens responsible for liquid crystalline order, one can create elastomers that will change shape in response to ultraviolet light. This provides a basis for a “write once, read many times” (WORM) memory. Information is encoded in an array of LCE microposts through a magnetic field during cross-linking, and then read out by introducing a light source. The system will return to its initial state upon removal of the stimulus, allowing the reading process to be repeated without altering the system. We developed a finite element simulation code to study components of such a system. Using our simulation method, we can predict the micropost deflection as a function of the preset nematic director and the incident angle of the light. We make comparisons to available experimental results and describe new findings that reveal how light can be used regulate the structure of an array of multiple, interacting LCE microposts. These studies point to new ways of utilizing the LCE arrays for technological applications. |
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L70.00200: Rolling Dynamics of Nanoscale Elastic Shells Driven by Active Particles Yuan Tian, Heyi Liang, Tingzhang Li, Andrey Dobrynin Self-propelled elastic shells capable of transducing energy to rolling motion could have potential applications as drug delivery vehicles. To understand the dynamics of the nanoscale elastic shells, we performed molecular dynamics simulations of elastic shells filled with a mixture of active and passive beads in contact with an elastic substrate. The energy transduction from active beads to elastic shell results in stationary, steady rolling, and accelerating states. In stationary state, the torque produced by friction force in the contact area balances that due to the external force generated by the active beads and the shell sticks to the substrate. In steady rolling state, rolling friction force balances the driving force, and the shell maintains a constant rolling velocity. Theoretical analysis shows a universal scaling relationship between the magnitude of driving force and shell velocity. This is a manifestation of viscoelastic nature of shell skin deformation dynamics during rolling motion. In accelerating state, energy supplied to the system by active beads exceeds the energy dissipation due to viscoelastic shell deformation in the contact area. Furthermore, the contact area of the shell with substrate decreases with increasing shell instantaneous velocity. |
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L70.00201: Phase Behaviour of Block Copolymer Pluronic: A Rheological Perspective KHUSHBOO SUMAN, Sagar Sourav, Yogesh M Joshi We study temperature induced phase change of a block copolymer Pluronic F127 (PEO100-PPO65-PEO100) over a concentration range of 20-35 wt%. While this temperature dependent phase change visually appears like a liquid-soft solid transition, termed as gel in the literature, there is a debate regarding precise microstructure of the soft solid state. In this work, we conduct frequency (ω) sweep at various temperatures on F127 solution. We observe that irrespective of the concentration, F127 solution shows all the rheological characteristics of sol – gel – glass transition. This suggests the transition of a liquid-like sample to a space spanning percolated network, whose rheological characteristic is increase in tan δ with ω, followed by a glass transition as characterized by a peak in tan δ. Interestingly, the maxima in tan δ shifts to lower temperatures with an increase in ω, which illustrates the rate dependence of glass transition. The temperature associated with the glass transition decreases with increase in F127 concentration. The glass transition behavior is also observed at high temperature during gel melting. Finally, we construct a phase diagram and correlate it w.r.t various phase diagrams of F127 available in the literature. |
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L70.00202: Anomalous apparent Poisson ratios in stiff semiflexible polymer networks Jordan Shivers, Sadjad Arzash, Fred C. MacKintosh Fibrous networks of stiff athermal biopolymers such as collagen, a major structural component of the extracellular matrix, have been shown to exhibit anomalously large apparent Poisson ratios, i.e. significant transverse contraction under small applied longitudinal extension. Here we show that this effect can be understood in the context of a macroscopic mechanical phase transition from a bending-dominated regime to a stretching-dominated regime at a critical applied extension controlled by the network connectivity. We measure this effect using a variety of 2D and 3D model network structures and propose a phase diagram governing the transition as a function of connectivity and strain. |
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L70.00203: Computationally modeling the use of digital holographic microscopy to characterize colloidal fractal aggregates Jerome Fung, Samantha Hoang Recent experiments suggest that digital holographic microscopy can be used to determine the average fractal dimension of an ensemble of colloidal fractal aggregates [1]. We present computational results that clarify the range of validity of this approach. In the experiments, an aggregate in solution is illuminated with coherent light, and the interference pattern formed between scattered and unscattered light, or hologram, is recorded. Fitting an effective-sphere scattering model to a hologram allows an effective radius reff and effective refractive index neff to be determined for each aggregate. Once reff and neff are determined for an ensemble of aggregates, a scaling relationship between reff and neff derived from the Maxwell Garnett effective medium theory yields the average fractal dimension. In our study, we computationally generate holograms of aggregates of known geometry (and hence, fractal dimension) and fit effective-sphere models to those holograms. We then determine whether the scaling relationship between reff and neff correctly determines the fractal dimension. Our results suggest that this approach is useful for loosely-packed aggregates whose extent does not greatly exceed the wavelength of the incident light. |
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L70.00204: Charge Transport and Electrode Polarization in Phosphonium Ionic Liquids Bearing Sulfonate and Carboxylate Anions Matthew Harris, James T Cosby, Durgesh Wagle, Gary Baker, Joshua Sangoro The impact of chemical structure on mesoscale organization and dynamics in a series of ionic liquids based on the tetradecyltrihexylphosphonium cation with various sulfonate and carboxylate anions has been studied using broadband dielectric spectroscopy and wide-angle X-ray scattering. The effects of anion structure on the mesoscale organization in the liquid and ion transport properties were interpreted based on current theoretical understanding. In addition, the phenomena of electrode polarization arising due to accumulation of ions at the electrode surface was analyzed with regard to mesoscale organization and bulk transport properties. Evidence of slow dynamics at the electrode/ionic liquid interface is observed and attributed to electrosorption. |
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L70.00205: Charge transport and structural dynamics in deep eutectic mixtures (DEMs) Stephanie Spittle, James T Cosby, Joshua Sangoro Charge transport and structural dynamics in choline chloride and glycerol mixtures were studied by broadband dielectric spectroscopy (BDS), dynamic mechanical spectroscopy (DMS), and differential scanning calorimetry (DSC). Slow sub-α relaxations are observed with BDS and DMS spectra. With decreasing choline chloride concentration, the sub-α dielectric relaxation, that is coupled to ion diffusion becomes much slower, while the slower mechanical relaxation is unaffected. This unexpected result is discussed within the framework of recent theories of ion transport and sub-α dynamics in small-molecule liquids. |
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L70.00206: Charge Transport and Ion Dynamics in Imidazolium-Based Homo- and Tri-Block Poly(Ionic Liquid)s Alexandre Horton, Emmanuel Mapesa, Mingtao Chen, Maximilian F Heres, Matthew Harris, Yangyang Wang, Timothy Long, Bradley Lokitz, Joshua Sangoro Broadband Dielectric Spectroscopy (BDS) and Differential Scanning Calorimetry (DSC) are used to probe ion dynamics in a series of imidazolium-based tri-block copolymers, and compared to their homopolymer analogues. Two calorimetric glass transitions are observed and assigned to the charged and uncharged (polystyrene) blocks. Exchanging bromide with bis(trifluoromethylsulfonyl)amide counter-ion, a change of the glass transition temperature by over 50 K is realized, bringing forth an increase in the room-temperature dc-ionic conductivity by over six (6) orders of magnitude. By systematically varying the volume fraction of the charged block, we demonstrate that the choice of counter-ion is the key parameter influencing charge transport in these systems. |
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L70.00207: Charge Transport and Dynamics of 2D-Confined Polymerized Ionic Liquid Blends Kaitlin Glynn, Thomas Kinsey, Joshua Sangoro The impact of geometrical confinement on ion transport and dynamics in molecular and polymerized is investigated by broadband dielectric spectroscopy. The monomers of ammonium based ionic liquids are filled into unidirectional silica nanopores with mean diameters of 7 nm and studied by Raman spectroscopy in situ to monitor the progress of monomer conversion. Ionic conductivity is also probed at different degrees of polymerization and compared to bulk blends of molecular and polymerized ionic liquids. In agreement with similar systems recently published, it is found that the ionic conductivity in polymerized ionic liquids in nanopores is enhanced compared to their bulk counterparts. The results are discussed within the current theoretical frameworks for describing dynamics and transport in confined polymers. |
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L70.00208: Molecular Dynamics in Poly(Methyl Methacrylate)/Silica Nanoparticle Composites Emmanuel Mapesa, Michael Kilbey, Dayton Street, Joshua Sangoro Broadband Dielectric Spectroscopy (BDS) and Differential Scanning Calorimetry (DSC) are employed to study molecular dynamics and glass transition temperature (Tg) in poly(methyl methacrylate) (PMMA)/Silica-nanoparticle (NP) composites. By systematically probing the case of bare (non-functionalized) Si-NPs dispersed in PMMA matrix and that of PMMA grafted Si-NPs in PMMA matrix, we isolate the effects of each of these cases on dynamics and Tg. Furthermore, we show – for the structural relaxation process – that in addition to slowed down mobility, which is commonly reported in literature and assigned to dynamics at the NP-matrix interface, faster modes also arise due to confinement effects. Scanning Electron Microscopy (SEM) is used to confirm uniform dispersion of the NPs. |
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L70.00209: 3D Printing Water-In-Water Ganhua Xie, Joe Forth, Yu Chai, Paul Ashby, Brett Helms, Thomas Russell One of the hallmarks of biology is the ability to compartmentalize and coordinate system functions, which has been difficult to reproduce even in the most sophisticated synthetic mimics. We show how to fabricate flexible, 3D structured water-in-water systems embodying both principles by using the interface of immiscible polymer solutions to generate tubular membranes held in shape by an elastic polyanion-polycation complex. Using a 3D printer, the length, shape, and diameter of printed tubules water-in-water systems can be controlled. We demonstrate directional diffusion and separation of ionic species confined to each liquid phase according to their preferential affinity for the polyelectrolyte in the opposite phase. By coupling compartmentalization with flow-driven directed material transport, continuous molecular separation can be achieved in such water-in-water systems. A layer-by-layer strategy is also used to further strengthen and functionalize the flexible tubules, significantly extending the potential applications of these all-aqueous 3D printed tubular systems. |
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L70.00210: The Manipulation of Granular Media Flow Properties to Produce Stable, Uphill, Low Mass Bipedal Locomotion Jonathan Gosyne, Daniel Goldman Unlike multileg robots which are typically close to the ground and generally statically stable, bipedal robots must maintain balance in potentially shifting terrain. We performed a series of systematic experiments to enable a 7 degree-of-freedom planar biped walker (45cm tall) to robustly traverse granular inclines of 0 to 10 deg of 1 mm poppy seeds. Through gait optimization, center of mass (CoM) variation, and contact-based control, a robust open-loop (OL) system for low mass biped robotic locomotion on granular media (GM) was developed. This was achieved through manipulation of step length, L, and vertical CoM to minimize GM flow at the foot-media boundary. Because of nonlinearities involved in GM deformation, typical body and joint stabilization techniques used in biped robotics over hard ground are insufficient. Thus, we developed a control scheme encompassing static inertial changes through torso position, and contact area variation through dynamic expansion of the feet, to redistribute slip forces (characterized by foot intrusion or material flow). This allows for robust, steady gait over GM, and have found that this scheme enables the robot to remain upright for the duration of a trial (5 gait cycles) 90% of the time, compared to consistent OL failure within 1 gait cycle. |
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L70.00211: Versatile and Robust Soft Untethered Robots with Tight Integration of Soft Actuators and Flex Circuitry that Navigating Through Unstructured Terrains Xiaonan Huang, Kitty Kumar, Mohammad Khalid Jawed, Zisheng Ye, Carmel Majidi Soft legged robots require robust walking dynamics and untethered functionality to approach the capability of their natural mammalian and reptilian counterparts to swiftly maneuver through unstructured environments. Achieving a soft robotics platform capable of biologically-relevant locomotion speeds depends on careful selection of actuators and electronics with soft materials and integration of power and control electronics. We demonstrate this with two untethered soft robotic testbeds that are both composed of flexible printed circuit board that integrates power and control electronics and electrically-powered soft limbs. The first implementation is a quadruped that is capable of walking at a maximum speed of 0.56 body length per second (3.2cm/s) and making 90 degree turns in two complete gait cycles (~5s). The second is a caterpillar-inspired robot capable of crawling with multiple gait at a speed of ~10mm/s over 25min. These robots are versatile and robust and have the capability of walking on a variety of surfaces, including up inclines, rocky terrain and poppy seeds, climbing over a half body height step, and maintaining continuous forward locomotion through confined space or after being dropped from an elevated height. |
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L70.00212: Self-Organization of Confined Binary Active Particles Wilson Luo, Mingfei Zhao, Xin Yong The emergent behavior of active systems with self-propelled particles can be found in nature at many length scales, from bird flocking to bacteria swarming. Most previous studies investigate the collective behavior of systems with uniform morphology. However, many biological systems function via the interactions between multiple distinct organisms, often with differing geometries. In this study, we investigate the interactions between active particles of differing morphology. Our system consists of a mixture of self-propelled rod-like and sphere-like particles which exert pairwise repulsive forces and torques on each other in a 2D confined domain. Segregation of rods and spheres into distinct clusters can be observed without any adhesion. Our study will provide important insight in phase separation and cell sorting in co-cultured organisms. |
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L70.00213: Stress Localization of Thin Sheets in a Cylindrical Geometry Nicole Voce, Klebert B Feitosa, Marcelo Azevedo Dias The ability to manipulate surface elastic instabilities finds many applications in engineering smart interfaces. We study the buckling phenomena of a thin cylindrical shell under axial compression that is constrained to slide onto an inner non-deformable pipe. Surface buckling is induced by immobilizing one end of the cylindrical shell and applying force to the other end. We study the geometry of the surface pattern, which is composed of rhombus shaped unit cells. We characterize the stress localization through shell thickness dependence and the out-of-plane deformation of the pattern after compression. Analysis of the curvature radii around the vertices of the unit cell shows that for thinner shells, the features get sharper suggesting that the stress is becoming more localized. Furthermore, as the thickness decreases, the distribution of the measured Gaussian curvature on the surface narrows around the zero mean indicating that the cylindrical shell is approaching the classical origami Yoshimura pattern. |
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L70.00214: Crystals and Liquids in Monolayers of Heavy particles Nisha Lama, Eric Weeks, Yijun Dong, Peiyao Wu, James T Kindt We use brightfield microscopy to observe a dense monolayer of heavy colloidal particles sedimented to the bottom of a sample chamber. In our system, we control two parameters: particle concentration and Peclet number (Pe). Pe measures the relative importance of the gravitational force over the thermal effects and is directly proportional to the particle diameter. We are trying to find how Pe and particle concentration influence the packing structure of the sedimented monolayer. When we compared our simulation data with our experimental results, we found that our experiments were significantly less ordered than the simulations. This led us to investigate the influence of polydispersity in our samples and experimental issues created by the unintended influence of gravity when the slide has a slight tilt away from the horizontal. |
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L70.00215: Compressible Colloidal Clusters from Pickering Emulsions and Their DNA Functionalization In-Seong Jo, Joon Suk Oh, Shin-Hyun Kim, David J Pine, Gi-Ra Yi In this study for DNA-mediated colloidal assembly with pre-assembled clusters, DNA sequences, areal density of DNA, particle number density and size ratio are key parameters for determining equilibrium structures. We developed a simple and facile method to produce compressible colloidal clusters were prepared by assembling azide-functionalized non-crosslinked polymer particles using fluorinated oil-in-water emulsion droplets. The particles were adsorbed onto the droplet interface, which were packed to form clusters during slow evaporation of the oil. Because we use non-crosslinked polystyrene particles for colloidal clusters instead, which can be merged partially through solvent annealing, the compression ratio can be precisely controlled. Then, the clusters were coated by DNA using an strain-promoted alkyne–azide cycloaddition reaction. As the particles are not crosslinked, the shape of the DNA-coated clusters can be further modified to control the compression ratio through plasticization. |
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L70.00216: Tuning the Temperature-Dependent Thermal Conductivity via Complex Colloidal Superstructures Fabian Nutz, Markus Retsch The ability to precisely tune the temperature dependence of the thermal conductivity possess a vital challenge to develop and conceive future heat management devices. In this contribution, we demonstrate the vast potential of polymer colloidal crystals to address and master these challenges. We achieve this goal based on the constriction-controlled thermal transport through well-defined colloidal crystal superstructures. These colloidal superstructures are specifically built by tailor-made latex particles with distinct glass transition temperatures. We exploit their multiresponsive film formation at various temperatures to demonstrate unprecedented control over thermal conductivity at temperatures between 25 °C and 200 °C. Based on the film formation process, we can irreversibly increase the thermal conductivity by a factor of about three. We show how to control: |
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L70.00217: Simulating Transmon Lattices for Analysing System Constraints in the Noisy Intermediate Quantum Scale Jonathon Miller Thermal noise from electrical circuit components and noise due to fluctuations in energy levels of Transmon circuits have the cumulative effect of decreasing the coherence time of these systems. As coupled Transmon systems scale to the noisy intermediate quantum scale, accurate characterization of noise accumulation and its effects on coherence time and quantum logic gate fidelity is vital. The answer this work aims to provide is the limitations on the coherence time imposed by the noise as the system scales from a few to many (50-100) qubits. The noise analysis is being carried out by a computational simulation of a linear Transmon chain forced into a confinement and surrounded by a bath of thermal photons characteristic of the circuit component radiation. A Generative Artificial Intelligence is used to explore the space of superconducting circuits to develop an understanding of the thermal constraints of a Noisy Intermediate Scale Quantum Computer. |
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L70.00218: de Gennes Narrowing in Colloidal Discs Namita Shokeen, Ashis Mukhopadhyay We studied the wave vector (q) dependence of relaxation time (τ) for different volume fractions of aqueous solutions of microspheres and microdiscs in concentrated regime. We observed characteristic peaks in τ(q) at certain q values. Such peaks indicate slow relaxations of structural rearrangements. These peaks match very well with the peaks in structure factor S(q) and radial distribution function g(r) calculations. This phenomena is called as de Gennes narrowing. |
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L70.00219: Dynamics of Polydispersed Emulsion Systems in a T-Shaped Chamber Kenny Nguyen, Xin Du Emulsions consist of droplets of one liquid mixed into another immiscible liquid. Our samples are oil-in-water emulsion droplets flowing through a T-shape chamber. By means of microscopy, we studied the influence of the polydispersity on the dynamics of emulsion droplets, analyzed the deformation profile of the droplets and compared the emulsions flow with stratified liquid flow. Our experimental results indicate that (1) monodispersed sample exhibited more jammed behavior than the polydispersed samples; (2) particles near the boundary move differently from those in the middle at the T-junction; (3) The flow of emulsion system exhibit more turbulence comparing with stratified flow; (4) smaller droplets moved faster and are less affected by cooperative motion of neighbor droplets. |
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L70.00220: Effect of Interfacial Rheology on the Properties of Polymerized High Internal Phase Emulsions Muchu Zhou, Reza Foudazi High internal phase emulsions (HIPEs) can be created when the volume fraction of dispersed phase exceeds 74%. Porous polymer materials can be produced through HIPE-templating approach. Polymerized high internal phase emulsions (polyHIPEs) are formed by polymerization of the continuous phase of HIPEs that contains the organic monomers and subsequent extraction of the dispersed phase. The porous interconnected structure of polyHIPE is achieved through the formation of small holes (also known as windows) on the polymer wall between droplets. The polyHIPEs can be used as adsorbents, ion-exchange resins, separation membranes, and scaffolds in tissue engineering due to their high porosity and low density. In order to meet the requirements of the specific applications, strategies to control the pore size and window size of the polyHIPEs are necessary to be investigated. In this study, different surfactant systems and mixing methods are employed to prepare the polyHIPEs with different pore and window sizes. We also study the effect of interfacial rheological properties of different surfactant systems at the interface of the aqueous and oil phases on the morphology, and thus, mechanical properties of final polyHIPEs. |
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L70.00221: Foam-templated macroporous polymers Ryan Zowada, Reza Foudazi Foam templates were produced by rapid gas dispersion into an aqueous monomer solution at various dispersion concentrations. Then, the templates were cured through free radical polymerization to obtain polydispersed solid foams. The foams were analyzed for their stability by measuring coarsening rates and drainage times to quantify and compare the effect of gas dispersion concentration. The foams exhibited yield stress with pseudoplastic behavior, so their flow curve was fitted using Herschel-Bulkley model to calculate the required foaming energy. The benefits of using a gas dispersion phase instead of a liquid phase is an increase in starting material efficiency and eliminating typical removal step of the disperse phase in foam-templating compared to emulsion-templating. We investigated the morphological characteristics and mechanical properties of obtained porous polymers from foam- and emulsion-templating methods. |
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L70.00222: Foamability of Aqueous Solutions of Charged Surfactants and of Surfactant-Polymer Mixtures Carina Martinez, Sophia Horowicz, Matthew Wagener, Vivek Sharma Dynamic adsorption of a freshly created interface is intimately linked with the rate of mass transfer of surfactant from liquid sub-phase to the interface, and this adsorption-limited kinetics is said to impact the stability of the newly formed interface. Addition of polymer to a surfactant solution affects the dynamic adsorption and the rheological response due to the formation of association complexes. Dynamic surface tension refers to the time dependent variation in surface tension, which is related with the rate of mass transfer of a surfactant from liquid sub-phase to the interface. Dynamic surface tension measurements carried out with conventional methods like pendant drop analysis, Wilhelmy plate, etc. are limited in their temporal resolution. In this study, we apply the method of maximum bubble pressure tensiometry for the measurement of dynamic surface tension effects at extremely short (1-50 ms) timescales. We discuss the overall adsorption kinetics of charged surfactants and the influence of added polymer on dynamic surface tension. Finally, we examine how pinch-off dynamics and rheological properties are modified in the presence of added polymers by including a critical examination of shear and extensional rheological responses. |
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L70.00223: Viscous fingering in lyotropic chromonic liquid crystals Shuang Zhou, Qing Zhang, Irmgard Bischofberger We studied the Saffman-Taylor instability in a Hele-Shaw cell containing nematic lyotropic chromonic liquid crystals. The coupling between the flow field and director field changes the effective viscosity of the liquid crystal, and therefore influences the patterns formed by the injected liquid. In particular, the hugely different viscosities for different distortion modes in chromonic liquid crystals play important roles in determining the patterns. Besides changing the viscosity of injected fluid and the injection rate, we can also control the pattern by changing the concentration of chromonics in water solution, which tunes the anisotropic viscosities. By quantitatively comparing the local director field with flow field, we show that the intrinsic anisotropy of the displaced liquid can lead to rich and controllable patterns in a Hele-Shaw cell setup. |
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L70.00224: Omnidirectional optical band gap for circularly polarized light in a nanocomposite cholesteric elastomer Guillermo Reyes, Adrian Reyes In recent years, Liquid Crystal Elastomers (LCE), have become very important in researchs, due to it's possible applications to manufacture many optical devices as filters, actuators or transductors. |
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L70.00225: Fast electro-optical switching of dichroic dye-doped antiferroelectric liquid crystals without polarizers Veridiana Garcia Guimarães, Junren Wang, Steven Planitzer, Rafael Soares Zola, Antal Istvan Jakli In this work we investigate alignment and electro-optical properties of a room temperature dye-doped antiferroelectric liquid crystal mixture. We achieved extremely uniform alignment on macroscopic scale of thin cells with the combination of proper surface alignment and electric field treatment. We have also successfully demonstrated that two films of dye-doped antiferroelectric liquid crystals in their anticlinic chiral smectic C (SmCA*) phase can be used to switch the transmitted light intensity between dark and bright states without the need of polarizer filters. We also demonstrate that one could get either normally dark or bright states. Normally dark states can be useful in number of applications such as in privacy windows or smart refrigerators. A normally transparent display has applications in plethora of other areas, such as navigation systems built in windshields, in goggles, or smart windows. |
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L70.00226: Amplification of chirality of lyotropic chromonic liquid crystals confined to capillaries Sujin Lee, Elsa Reichmanis, Jung Ok Park, Mohan Srinivasarao Lyotropic chromonic liquid crystals (LCLC) molecules are achiral, that have plank-like rigid aromatic cores and hydrophilic ionic groups at the peripheries. Upon confinement of LCLCs in cylindrical capillary, the director adopts a doubly twisted director configuration, due to unusually small twist elastic constants in LCLCs. Since the LCLC is achiral, they possess multi domain with equal probability of both handedness which is separated by Neel walls. In this work, we report that by adding minute amounts of chiral molecules to LCLCs with a doubly twisted director configuration possessing both handedness, the whole system can be transformed into a single handedness. The structure and charge of the chiral molecules were also studied. By investigating the effect of various chiral molecules within this LCLCs in capillary system, we expect to understand chirality amplification mechanisms. |
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L70.00227: Repeated rehydration of lipid films as a method to mix phospholipids without the use of organic solvents. Eric Oropeza-Guzman A technically simple method for mixing phospholipids of different species without using organic solvents or additives has been developed. Based on the reported literature regarding aqueous lamellar systems, phospholipid interaction parameters, and lipid diffusion coefficients, we hypothesized that the repeated drying and rehydration of a multispecies phospholipid sample, using only deionized water, should produce a uniform distribution of phospholipid molecules. Different lipid films of binary mixtures of zwitterionic and anionic glycerophospholipids were prepared using this method. The resulting films were reconstituted in vesicular form and compared to controls prepared with organic solvents by differential scanning calorimetry. The calorimetric scans revealed no significant differences between samples and controls for any of the tested mixtures. This finding suggests that the proposed technique creates a product with equivalent compositional homogeneity than the conventional method. From an environmental, health and safety standpoint, we are confident that this technique can contribute to the implementation of sustainable chemical practices, especially in industrial settings where organic solvents are tightly regulated. |
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L70.00228: Self-assembly of cyclic polygon shaped fluid colloidal membranes through pinning Lachit Saikia, Prerna Sharma An isotropic mixture of rod-like viruses self-assembles into 2D fluid monolayer membranes in presence of non-adsorbing polymer through depletion attraction. These membranes are circular in shape due to surface tension. Surprisingly, cyclic polygon shaped colloidal membranes form when isotropic mixtures of two kinds of geometrically different rods are mixed with depleting polymer. Long rods form faceted core of the cyclic polygon whereas short rods phase separate into lobes that are connected through pinning points. We demonstrate that the origin of this stable out of equilibrium anisotropic shape of the membranes lies in the phenomenon of how one fluid membrane spreads over another in presence of disorder/pinning sites. We show that the pinning sites are not topological defects rather accumulation point of rods that are significantly different. Our results show a unique counter-intuitive scenario where disorder leads to self-assembly of ordered structure. |
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L70.00229: Structure of Lung-Mimetic Multilamellar Bodies with Lipid Compositions Relevant in Pneumonia Dylan Steer, Sherry Leung, Hannah Meiselman, Daniel Topgaard, Cecilia Leal Pneumonia is the leading cause of death amongst captive dolphins. While the pathology of pneumonia is understood at a macroscopic level, recent results show that changes in material chemistry at the lung-air interface plays an important role in symptoms, though the physical basis is unknown.[1] Healthy lungs are coated by a thin, hydrated biological composite composed primarily of amphiphilic lipids and a small amount of proteins. These self-assemble into liquid-crystalline phases which can reduce the fluid-air interfacial surface energy to near 0. In diseased lungs abnormally high concentrations of cardiolipin, a highly charged and highly unsaturated lipid, and Ca2+ can be found. Here we observe using small angle X-ray diffraction (SAXS) that addition of cardiolipin dehydrates the lipid membranes, contrary to predictions of pure electric double layer theory. The physical cause for these effects and the influence of Ca2+ is studied using wide angle X-ray diffraction (WAXS) and solid state nuclear magnetic resonance (ssNMR). |
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L70.00230: Colloidal Gelation of Thermo-Responsive Microgel Mixture Suspensions SAORI MINAMI, TAKUMI WATANABE, DAISUKE SUZUKI, Kenji Urayama Concentrated suspensions of microgels composed of thermo-responsive polymer such as poly(N-isopropylacrylamide) (PNIPA) exhibit various states, i.e., repulsive glass, dispersion, (attractive) colloidal gel, depending on temperature (T), particle concentration, surface charge density. The heating reduces the volume of the microgels, and also substantially changes the type of interparticle interaction from repulsive to attractive when T across the LCST, resulting in the formation of colloidal gel. Present work focuses on the dense suspensions of the microgel mixtures of PNIPA and the homologue with different LCSTs. We show that the rheological properties of the mixture suspensions are pronouncedly affected by the mixing ratio. The T-dependent viscoelastic properties of the mixture suspensions are interpreted by considering the T-dependence of the volume fraction and the type of interparticle interaction of each component.[1] |
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L70.00231: Thermoelastic heterogenity in a model metallic glass from molecular dynamics calculations Baoshuang Shang, Pengfei Guan, Jean-Louis BARRAT It is well known that the elastic properties of amorphous systems are heterogeneous, leading to peculiarities in vibrational spectra and thermal properties. In this work, we investigate the heterogeneity in thermoelastic properties, and more precisely in the thermal expansion coefficient, in a model metallic glass. We find heterogeneities that are similar - in terms of length scales - to those in elastic constants. It has been suggested that such heterogeneities could be the reason for "cryogenic rejuvenation" processes observed under thermal cycling in several experiments. We investigate this hypothesis by comparing the values of the local yield stresses with the stresses generated by heterogeneities in thermal dilation. |
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L70.00232: Terahertz Time-Domain Spectroscopy and Low-Temperature Specific Heat Investigation of Vitreous Glucose Tatsuya Mori, Mikitoshi Kabeya, Suguru Kitani, Yasuhiro Fujii, Jae-Hyon Ko, Akitoshi Koreeda, Hitoshi Kawaji, Seiji Kojima The boson peak is a low energy excitation universally observed in the THz region of the amorphous materials. The boson peak of infrared spectra appears in the spectra of α(ν)/ν2 [α(ν) is the absorption coefficient]. In this study, we performed terahertz time-domain spectroscopy on glassy glucose to investigate the boson peak dynamics. Moreover, we determined infrared light-vibration coupling coefficient using the α(ν) and vibrational density of states obtained from the low-temperature specific heat measurement. |
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L70.00233: Mechanics of filamentous growth in soft materials Nicolas Bruot, Nino Kukhaleishvili, Charles Puerner, D. Thompson, Agnese Seminara, Martine Bassilana, Robert Arkowitz, Xavier Noblin Candida albicans is a yeast that grows in the shape of a filament with a tip continuously moving forward in the nutritious medium. The forces at the tip are driven by the internal pressure of the cell and are strong enough to induce indentation and penetration in materials such as the human tissues. This allows C. albicans to invade a host, with possibly lethal consequences, especially in immunodeficient individuals. |
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L70.00234: DNA-Functionalized 100 nm Polymer Nanoparticles from Block Copolymer Micelles JeongHoon Yoon, Saerom Lee, In-Seong Jo, Joon Suk Oh, David J Pine, Tae soup shim, Gi-Ra Yi DNA-mediated self-assembly of colloidal particles is one of the most promising approaches for constructing colloidal superstructures. For nanophotonic materials and devices, DNA-functionalized colloids with diameters of around 100 nm are essential building blocks. Here, we demonstrate a strategy for synthesizing DNA-functionalized polymer nanoparticles (DNA-polyNPs) in the size range of 55~150 nm using block copolymer micelles as a template. Diblock copolymers of polystyrene-b-poly(ethylene oxide) with an azide end group are first formed into spherical micelles. Then, micelle cores are swollen with styrene monomer and polymerized, thus producing PS nanoparticles with PEO brushes and azide functional end groups. DNA strands are conjugated onto the ends of the PEO brushes on the surface of PS particles through a strain-promoted alkyne-azide cycloaddition reaction (SPAAC). The DNA-polyNP with complementary sequences show thermally-responsive association and dissociation behavior |
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L70.00235: Geometry-driven self-assembly of interfacial sheets Zachariah Schrecengost, Jordan V Barrett, Vincent Démery, Joseph D Paulsen
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L70.00236: Hierarchical Self-assembly, Spongy Architecture and Phase States of Laponite in water-Alcohol mixtures RAVI KUMAR PUJALA We propose an alternative method to tune the electrostatic interactions to obtain a transition from a repulsive to an attractive system of nanoplatelets by increasing the alcohol concentration, i.e. increasing the Bjerrum length. A phase diagram of Laponite® in alcohol solutions has been proposed, which clearly demarcates regions of stable sol, unstable sol, transparent gel, turbid gel, glass, and flocculation. A new class of soft materials, called nanoclay-organogels, was deeply explored using confocal and scanning electron microscopy that depicted spongy architecture and presence of nano and micron size pores inside the gel matrix indicating the hierarchical self-assembly of the nanoplatelets in the binary solvent. Universal power-law scaling of storage modulus and yield stress with alcohol concentration was observed. We have extensively examined the dispersion stability, aggregation and gelation behaviour of Laponite nanoplatelets in different alcohol -water binary solvents, thereby proposing a universal description of nanoclay dispersion in alcoholic solutions, which is poorly probed and marginally understood in the literature. |
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L70.00237: Liquid Magnets Xubo Liu, Noah Kent, Alejandro Ceballos, Joe Forth, Shaowei Shi, Dong Wang, Thomas Russell Dispersions of carboxylated iron oxide magnetic nanoparticle (Fe3O4-COOH MNP) with a diameter of 30nm are a type of ferrofluid that is superparamagnetic under normal conditions. Here, we demonstrate a simple approach to reversibly transform a paramagnetic ferrofluid droplet into the ferromagnetic state by immersing it into an immiscible liquid containing ligands, that can interact with the particle to form MNP-surfactants that subsequently are brought into the jammed state. As a result, a novel ferromagnetic liquid device, namely a liquid magnet, is generated in one step. The liquid magnet is a functional core-shell structure, with a superparamagnetic fluid core wrapped by a monolayer shell of jammed ferromagnetic MNPs-surfactants, where the thermal energy of the active MNPs is weakened significantly by anchored ligands. The magnetic dipole moment of the ferrofluid is able to be maintained indefinitely. There is a measurable coercivity and remnant magnetization of the ferromagnetic liquid droplet. Under the influence of a rotating permanent magnet, the liquid droplets are seen to rotate at an angular velocity that increases with decreasing droplet size. The angular velocity is also found to increase with increasing time and reach a limiting velocity. |
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L70.00238: Dimerization of Annular Sector Particles Elyse Rood, Scott Franklin, Theodore Anthony Brzinski, Sykes Cargile We study annular sector particles (ASPs), open semi-circular rings characterized by two dimensionless numbers: the subtended opening angle and the ratio of inner and outer radii. The ASPs are placed in an annulus with a rotating, ridged ring above them. Applying a torque to this ring exerts a shear stress on the quasi-2D packing of ASPs. Within the annulus, if two ASPs are within the outer radius distance from each other they have the potential to intersect with each other. This entangled pair of ASPs is defined as a dimer. The movement of ASPs results in the formation as well as annihilation of dimers, known as dimerization and de-dimerization. |
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L70.00239: STATISTICAL AND NONLINEAR PHYSICS
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L70.00240: Predicting Network Edge Count and Fragmentation under Vertex Percolation Processes Nicholas Brunk, William Butske, James Alexander Glazier Network and graph-based percolation theory are applicable to a broad range of disciplines throughout the natural, life, and social sciences. We present a graph-based vertex (site) percolation study empirically quantifying – as a function of vertex occupation fraction – the number of edges (bonds) formed, the extent of fragmentation of the network, and the scaling of percolation thresholds with the mean vertex degree of the graph. The edge count is shown to be quadratically dependent upon the vertex occupation fraction with no unknown fitting parameters, thus applying universally - that is, to all networks - with minimal error. It may be used to predict, for example, the number of nearest neighbor bonds remaining in a lattice (e.g. translational degrees of freedom in a spatial lattice) or the number of friendships remaining as a social network is deconstructed (e.g. due to account closure on social media or mortality). For well-behaved networks with a reasonably low variance in the vertex degree distribution, the latter relations may be used to predict fragmentation: both the percolation threshold and, subsequently, the number of distinct connected components in the network at a given occupation fraction. |
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L70.00241: Optimal deployment of resources for maximizing impact in spreading processes Andrey Lokhov, David Saad The effective use of limited resources for controlling spreading processes on networks is of prime significance in diverse contexts, ranging from the identification of “influential spreaders” for maximizing information dissemination and targeted interventions in regulatory networks, to the development of mitigation policies for infectious diseases and financial contagion in economic systems. Solutions for these optimization tasks that are based purely on topological arguments are not fully satisfactory; in realistic settings, the problem is often characterized by heterogeneous interactions and requires interventions in a dynamic fashion over a finite time window via a restricted set of controllable nodes. The optimal distribution of available resources hence results from an interplay between network topology and spreading dynamics. We show how these problems can be addressed as particular instances of a universal analytical framework based on a scalable dynamic message-passing approach and demonstrate the efficacy of the method on a variety of real-world examples. |
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L70.00242: Electromechanical Instability of a Dielectric Elastomer Balloon Shengqiang Cai As an electroactive polymer, dielectric elastomer has been recently intensively explored in different engineering applications, ranging from soft robot, haptic devices, artificial muscle to energy harvesting system. In the applications, inflated dielectric elastomer balloons of various shapes have been widely adopted. Some recent experiments have shown unusual instability modes in dielectric elastomer balloon, when it is subjected to an internal pressure and electric voltage. |
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L70.00243: Cross-Influence of Thermodynamic Driving Forces in Confined Environment Yu Qiao, Meng Wang The second law of thermodynamics dictates that under a certain condition, the cross-influences of thermodynamic driving forces (tdf) must be balanced. For a galvanic cell, it is equivalent to the well-known Nernst equation; for a double-layer supercapacitor, it is consistent with the classic Gouy-Chapman model. In our recent experiment on confined large pivalate ions in carbon nanopores, however, it was measured that the cross-influences of the electromotive force and the chemical potential were different from each other by an order of magnitude. We attribute this remarkable phenomenon to the confinement effect of the electrode inner surfaces, which forbids the formation of diffuse layer. We argue that in general, in a low-dimensional environment, in the large dimension(s), the laws of classic statistical physics can be applied; but in the small dimension(s) wherein two tdf interact, the governing equations can be distinct. With this unique mechanism, the second law of thermodynamics may break down, in a dissimilar manner to “Maxwell’s demon”. The concept of unbalanced cross-influence of tdf is further examined through a theoretical analysis on a model system comprising of randomly moving elastic particles restricted in a two-dimensional transition zone in a gravitational field. |
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L70.00244: Fractional Lengevin equation with reflecting barrier Sarah Skinner, Thomas Vojta The Fractional Langevin equation describes a the motion of a particle under the influence of a random force with long-time correlations. This stochastic differential equation is a common model for anomalous diffusion. We investigate the fractional Langevin equation in the presence of a reflecting wall using Monte Carlo simulations. The mean-square displacement shows the expected anomalous diffusion behavior, 〈x^2〉 ∼ t2-α , as in the unconfined case. However, the probability density close to the wall shows highly non-Gaussian behavior. For reference, we compare our results to reflected fractional Brownian motion for which the probability density shows a power law singularity at the barrier [1]. |
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L70.00245: Fractional Brownian Motion with an Absorbing Wall Alex Warhover, Thomas Vojta Fractional Brownian motion, a random walk with long-time power-law correlations between its steps, is a prototypical model for anomalous diffusion. We employ large scale Monte Carlo simulations to investigate fractional Brownian motion in the presence of an absorbing wall. In the limit of vanishing correlations, our findings reproduce the well-known results for normal diffusion. In contrast, the interplay between the absorbing wall and the long-range power correlations leads to a singular probability density close to the wall. We compare our results to those of Brownian Motion in the presence of a reflecting wall [1], and we discuss implications of our results. |
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L70.00246: Oscillatory force generation in nonequilibrium systems from peaked energy spectra. Anthony Bonfils, Woosok Moon, Dhrubaditya MITRA, John Wettlaufer A key to force generation in non-equilibrium systems is encoded in their energy fluctuation spectra. A non-equipartition of energy, which is only possible in active or forced systems, can lead to a non-monotonic fluctuation spectrum. Recently, it has been shown that for a narrow, unimodal spectrum, the force exerted by a non-equilibrium system on two walls embedded in a system with such a spectrum oscillates between repulsion and attraction as a function of wall separation [1]. These results are consistent with the Maritime Casimir effect, which is driven by wind-water interactions, and with recent simulations of active Brownian particles. The spectrum is believed to be the solution of a specific class of Fokker-Planck equations. Taking a hydrodynamic perspective of Janssen [2], we construct a theory and a numerical basis for the observed Pierson and Moskovitz spectrum, which underlies the Maritime Casimir effect. |
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L70.00247: Counterintuitive asymmetry of transition times in the Brownian asymmetric simple exclusion process Dominik Lips, Artem Ryabov, Philipp Maass Driven diffusion of hard spheres (rods) in a one-dimensional cosine potential under a static bias should reflect properties of the asymmetric simple exclusion process (ASEP) on a lattice, if the amplitude of the cosine potential is considered to be large compared to the particles’ thermal energy. For this Brownian asymmetric exclusion process (BASEP) [1], we study transition times of a tagged particle between potential wells against and along the bias direction in non-equilibrium steady states. These transition times exhibit a counterintuitive asymmetry: While one may expect that the mean transition time in bias direction is shorter, the opposite is true. We relate this surprising asymmetry to the collective motion of the particles. Differences in the distributions of the times in and against bias direction depend sensitively on the filling factor (number of particles per potential well) and the rod length. Our analysis sheds light on the transport behavior of the model, which, compared to the ASEP, shows richer properties due to the additional length scale given by the rod length. |
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L70.00248: Imperfections by Design: Interactive Buckling and postbuckling in Architected Materials Yinghao Zhao, Amal Jerald Joseph Maria Joseph, Chunping Ma, Megan Skibinski, Burak Gul, Andrew Schellenberg, Nan Hu Harnessing elastic instabilities in materials has recently enabled new classes of tunable systems and devices, such as gating mechanisms, artificial muscles, and soft robotics, etc. The common feature of those instability-induced smart systems is the amplification of force and motion compared to their traditional stiff counterparts. Achieving these amplifying effects usually relies on harnessing tailorable architected materials as the building block. One of the challenges is how defects change the properties of architected materials to achieve targeted functions with aperiodic materials. In response to such need, we introduce a class of shell structures which undergoes interactive buckling. By combining finite-element simulations and desktop-scale experiments, we found that the interactive buckling can be induced by strategically controlling the number and the distribution of defects, leading to a deterministic actuation response compared to the one without geometric defects. Our study thereby opens avenues for the design of next-generation actuators and robots with high fidelity and low sensitivity over a wide range of length scales. |
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L70.00249: Scaling Features as Universal Hallmark of Physiological Dynamics across Systems , States and Clinical Conditions Plamen Ivanov We will present a review of linear and nonlinear scaling characteristics in physiological dynamics, their universality across systems, phase transitions across physiological states, relation to underlying control mechanisms and their relevance for diagnosis and prognosis of disease. |
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L70.00250: Discrete Bound States in a Floquet-Bloch Active Spinning System Shahrzad Yazdi, Alfredo Alexander-Katz Inspired by electronic systems, we explore the transport of an active spinning particle in a lattice of posts using a periodic driving protocol akin to a Floquet system. In our 2D Floquet-Bloch system, coupling of hydrodynamic and electrostatic interactions leads to hybridization of localized states of the spinning particle that are able to diffuse through the medium, or in some cases move ballistically. More interestingly, we find a set of discrete localized states at quantized applied frequencies that delimit regions of diffusion. These states have typical orbits much larger than the original localized states. They occur approximately at fractional frequency values of the two frequencies for the localized trivial states. Our results may be an interesting new view on transport in active colloidal systems and their counterparts in solid state physics. |
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L70.00251: Tunable Failure in Non-periodic Architected Materials Inspired by Slime Mold Growth Chunping Ma, Hanqing Zhang, Daobo Zhang, Peng Feng, Burak Gul, Nan Hu The field of architected materials has been explored in many disciplines over the past decade, it has yet to be fully explored in civil engineering and architecture. From the perspective of material constitution, most existing efforts on metamaterials primarily use the elastic buckling of soft materials, while common infrastructure materials lack the ability to undergo such large deformation/strain. In addition, most studies to date have maintained the symmetry of material and studied the simple periodic form. Inspired by slime mold growth, we explored a new class of non-periodic cellular materials and conducted proof-of-concept experiments on 3D-printed specimens. We found that simple changes on the archetectures of material can lead to significant differences in failure mechanism. Therefore, this study paves the road for the future design of resilient infrastructure involving the ability to rebound from extreme events and the corresponding repair approaches to recover capacity after those events. |
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L70.00252: Predicting shear transformation events in glasses via energy landscape sampling Bin Xu, Michael Falk, Jinfu Li, Lingti Kong Shear transformation (ST) events, as the elementary process for plastic deformation of glasses, are of vital importance to understand the mechanical behavior of glasses. Here, by characterizing first-order saddle points in the potential energy landscape, we develop a framework to characterize and to predict the triggering (i.e. locations, triggering strains, and local structural transformations under different shear protocols) of ST events. Verification undertaken with a model Cu-Zr glass reveals that the predictions agree well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses. |
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L70.00253: Machine Learning on Lithium Sulfur Materials Ying Li Materials properties are collective phenomena in a nonlinear relationship of compositions and interatomic configurations, which are difficult to acquire from computations. Interactions between the constituent particles (atoms) are so complicated which only the limited scale of the problem is analytically solvable with descriptive theory (e.g., density functional theory, molecular dynamics, etc.) combining with current high-performance computing technology. To generalize materials simulation and properties prediction, data-driven approaches (e.g., machine learning, neural network, etc.) are much needed. Here, we provide an example showing how the cohesive energy, Fermi energy and band structures of lithium-sulfur materials as intrinsic collective behaviors are learned via Machine Learning methods, such as random forest, K-nearest neighbor algorithm, LASSO, Neural Networks, etc, and the performance comparison of the different methods will be demonstrated, which provides a general design guidance for lithium-sulfur batteries. |
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L70.00254: Behavior of a Non-equilibrium Self-Organizing System: A Potential Means to Enhance Energy Efficiency in Systems with Functional Intelligence Gao(Zachary) Sun, Zhou Xu, Kun Wang, Buqin Wang, Mark T. Tuominen Research and development efforts in so-called artificial intelligence has increased dramatically. However, designing AI with energy efficiency is becoming an important priority. It is not yet clear how this should be done. One possible inspiration is to study the physics of self-organizing systems, both non-living and living, as guidance for future designs with functional intelligence. Irreversible processes at non-equilibrium can drive a system to self-organize and exhibit characteristics shown in systems known as dissipative structures. Our research explores the characteristics of experiments that use electrically conductive beads in an applied electric field. The setup resembles a primitive dissipative structure that can be interpreted as a possible bridge between behaviors in non-living and living systems. Using video and electrical measurements, we investigate the transient and steady-state behavior of self-organizing worm-like behavior under a range of initial and driving conditions. The non-equilibrium processes of a non-living system exhibiting characteristics that also exist within a living system are a possible way to explore biomimetic structures that exhibit intelligence. |
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L70.00255: Dynamics of Driven Diffusive Systems with Interactions and with Langmuir kinetics Tripti Midha, Anatoly Boris Kolomeisky, Arvind Kumar Gupta Driven diffusive system belongs to a special class of nonequilibrium systems that has wide applications in biological and vehicular transport processes. During intracellular transport of vesicles along microtubules, motor proteins interact among each other as well as frequently associate and dissociate from the tracks. Motivated by the above phenomenon, we develop a model that assimilates the interactions along with the nonconserved Langmuir kinetics in a totally asymmetric simple exclusion process [1]. We find that the continuum version of the simple mean-field (SMF) approach fails to handle strong correlations in the system. To incorporate the effect of correlation, we analyze the model using the correlated cluster mean-field theory. We compute the stationary phase diagrams, density, current and correlation profiles along the lattice for the various strength of attractive and repulsive interaction energy. Our results are in excellent agreement with the Monte Carlo computer simulations. For the case of attractions, we find the two-point correlation function to be stronger at the position of localized shocks. |
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L70.00256: Least Rattling Feedback from Strong Time-scale Separation Pavel Chvykov, Jeremy L England Many interesting dynamical systems in the world have a hierarchical structure. Here we explore how to leverage this structure to better understand and predict such systems. We assume that the dynamics on different scales can be viewed as independent, except for a clearly defined feedback loop: the slow motion defines the environment that fast dynamics live in, while fast motion maintains the rules governing effective slow dynamics. Focusing on this feedback loop, rather than the details of the fast or slow motion, may pave the way for generalizable insights about hierarchical systems. We illustrate on toy examples. |
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L70.00257: Janus Colloidal Crystal, a New Model System for Spin Ice and Glass Myeonggon Park, Steve Granick Questions like the dynamics of magnetic monopole in spin ice and the translation -rotation coupling in molecular glass have long puzzled scientists in different communities, mainly because it is hard to monitor the dynamics of these systems on microscopic level. Here we try to address these questions using Janus colloidal crystals, in which both the translational and rotational motions of particles can be tracked by video microscopy and the particle interaction can be finely tuned by electric field. as one of the results, we find that glasslike dynamics for rotational motion appears when the area fraction is so high that the system is crystalline. Our experimental system paves the way for modeling a wide range of phenomenon in spin ice and molecular glasses. |
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L70.00258: Jamming with Pins: How do different pin geometries affect jamming? Brian Jenike, Tristan Cates, Amy Graves We simulate two-dimensional, zero temperature systems of soft disks with harmonic repulsive pair potentials. The pin lattices contain disks that employ the same potential, but are of negligible size. We study square, triangular, honeycomb, and random lattices. That is, it has been known for several years that the jamming threshold, φj, decreases with pin density, ρ. At low pin densities, all lattice geometries produce the same φj(ρ) which decreases linearly with ρ, but pin lattice geometry begins to matter as ρ increases further. At low densities, as expected, all lattices are equivalent with a linear dependence on ρ. At moderate densities, the square lattice supports jamming better than the random lattice; but interestingly, at higher densities the situation is reversed. We present data on φj parameterized by lattice constant and lattice density; and on structural features such as distributions of contacts and angular ordering of bonds between particles. |
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L70.00259: Relaxation Dynamics after the Removal of a Static Force: Binary Operators and Impact of Eigenstate Thermalization Jonas Richter, Jacek Herbrych, Jochen Gemmer, Robin Steinigeweg We study the relaxation dynamics of expectation values under unitary time evolution for a certain class of initial states. The latter are thermal states of the quantum system in the presence of an additional static force which, however, become nonequilibrium states when this force is eventually removed. While for weak forces the dynamics is well captured by linear response theory (LRT), the case of strong forces, i.e., initial states far away from equilibrium, is highly nontrivial. |
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L70.00260: Disruption and Recovery of Reaction-Diffusion Wavefronts Colliding with Obstacles Rebecca Glaser, Nathaniel Smith, Vincent W.H. Hui, John Lindner, Niklas Manz We study the damage to and restoration of planar reaction-diffusion wavefronts colliding with convex obstacles in narrow two-dimensional channels using finite-difference numerical integration of the Tyson-Fife reduction of the Oregonator model of the Belousov-Zhabotinsky reaction. We characterize the obstacles' effects on the wavefront shape by plotting wavefront delay versus time. Due to the curvature dependent wavefront velocities, the initial planar wavefront (or iso-concentration line) is restored after a relaxation period that can be characterized by a power-law. We find that recovery times are insensitive to obstacle concatenation or to the upstream obstacle shape but are sensitive to the downstream shape, with a vertical back side causing the longest disruption. Delays vary cyclically with obstacle orientations. The relaxation power-laws confirm that larger obstacles produce larger wavefront delays and longer recovery times, and for a given area larger obstacle width-to-length ratios produce longer delays. Possible applications include elucidating the effect of inhomogeneities on wavefront recovery in cardiac tissue. |
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L70.00261: Many-Body Dynamic Localization Effect in Periodically Driven Finite Clusters of Spins 1/2 without Disorder Boris Fine, Kai Ji We investigate numerically and analytically the heating process in ergodic clusters of interacting spins 1=2 subjected to periodic pulses of an external magnetic field. Our findings indicate that many-body dynamic localization manifests itself as a cluster-size-dependent threshold for the pulse strength below which the heating is suppressed. This threshold decreases with the increase of the cluster size, approaching zero in the thermodynamic limit. Nevertheless, it should be observable in clusters with fairly large Hilbert spaces. We obtain the above threshold quantitatively as a condition for the breakdown of the golden rule in the second-order perturbation theory. |
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L70.00262: The thermodynamics of computing with finite automata David Wolpert, Artemy Kolchinsky Recent breakthroughs in stochastic thermodynamics have greatly enriched our understanding of the thermodynamics of computation. To date, these analyses have concentrated on the “computation” of erasing a single bit. One of the idiosyncratic characteristics of such computation is that we know ahead of time when it will finish, and so do not need to continually observe it to tell whether it has finished - thereby avoiding the thermodynamic costs of such observation. Here we show how to analyze the thermodynamic costs of running a computer without continually observing it even though its finishing time is random, e.g., because it depends on the random input to the computer. We then use this to analyze the thermodynamics of finite automata (FA), one of the most important types of computational system. In particular, we show that due to the variability in the number of iterations it takes a given FA to finish, the Landauer cost of running that FA is a sum of novel information theoretic quantities, which we call “partial entropies”. |
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L70.00263: Spatiotemporal tiling of the Kuramoto-Sivashinsky equation Matthew Gudorf, Predrag Cvitanovic Numerical simulations play a very important role in the study of chaotic partial differential equations due to the lack of analytic solutions. In the limit of strong chaos and or turbulence, these computations become very challenging if not completely intractible. In an attempt to circumvent these difficulties, we recast time dynamical systems as purely spatiotemporal problems in (d+1) dimensional spacetime. Specifically, the focus of this study will be on the spatiotemporal Kuramoto-Sivashinsky equation, a (1+1) dimensional system. Our main hypothesis is that spatiotemporal recurrences resultant from shadowing of invariant 2-tori are of critical import. This intuition is a spatiotemporal parody derived from the theory of cycle expansions [1]. By developing a (1+1) dimensional symbolic dynamics with invariant 2-tori as the fundamental building blocks, we hope to quantitatively characterize infinite spacetime solutions. |
(Author Not Attending)
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L70.00264: Propagation of light-sensitive reaction-diffusion waves in inhomogeneously illuminated systems Daniel Blaikie, Spencer L. Kirn, Niklas Manz The propagation dynamics of reaction-diffusion (RD) waves in illuminated quasi-2-dimensional systems was investigated, using various light-sensitive chemical Belousov-Zhabotinsky (BZ) reactions. Illuminating the BZ waves from below with visible light with a checkerboard pattern was used to change the light intensity in a repeating pattern, thus changing the speed of the light-sensitive waves. In our system, BZ waves slow down at higher illumination levels. Using a Ruthenium based catalyst, a light-sensitive BZ solution was made and absorbed by a filter paper to create the quasi-2D system. As the wave propagated over the checkerboard pattern of the illuminated system, the changes in speed would cause the wave to curve forward (dark area) and backward (bright area). The curvature should alternate and increase the overall speed of the wave as shown numerically by Schebesch and Engel in Phys.~Rev.~E 60(6) 1999. We used various catalysts, light intensities, illumination patterns, and BZ-component concentrations to determine how different excitation waves propagate through non-homogeneous excitation pattern. |
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L70.00265: Structural Vulnerability of Quantum Networks Angkun Wu, Liang Tian, Yang-Yu Liu Quantum networks allow for the transmission of quantum information between physically separated quantum processors. They play a very important role in quantum computing and quantum communication. Previous studies show clear advantages of establishing long-distance entanglement between two nodes in a quantum network for communication. Yet, the general structural vulnerability of such quantum networks has not been studied. Here we systematically examine two key notions in graph theory: articulation points (APs) and bridges, which ensure the connectivity of a network and naturally represent potential targets of attack if one aims for immediate damage to a network. We offer an analytical framework to calculate the fraction of APs and bridges for quantum networks with arbitrary degree distribution. We find that quantum networks with swap operations have lower fractions of APs and bridges than their classical counterparts. Moreover, we find that quantum networks under low degree swap operations are substantially more robust against AP attacks than their classical counterparts. These results help us better understand the structural vulnerability of such quantum networks. |
(Author Not Attending)
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L70.00266: Human Information Processing in Complex Networks Ari E Kahn, Christopher Lynn, Lia Papadopoulos, Danielle Bassett A curious aspect of information is its relativity: the amount of information contained in a message depends not just on its content, but also on the expectations of a receiver. Nowhere is this observation more evident, nor are the implications more important, than in the context of human cognition. Here, we develop an analytical framework for measuring information relative to human expectations, and we demonstrate its utility in two distinct ways. First, we verify that our framework predicts aspects of human behavior that cannot be accounted for by traditional information theoretical measures such as entropy. Second, we apply our framework to characterize the network structure of designed information sources, such as the network topology of natural languages and the structure of note transitions in music. Across a range of real-world networks, we discover that their inherent complexity is high while their divergence from human expectations is low, thereby allowing for the efficient communication of information. We find that this competition between high complexity and low divergence from expectations is driven by hierarchically modular organization, which, interestingly, has been observed in many evolved and designed networks. |
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L70.00267: Coarse-graining of Dynamics in Weakly Non-linear Processes on Networks Nima Dehmamy, Yanchen Liu It is known that if the graph has a hierarchical structure, many dynamical processes exhibit transient states in which the dynamics synchronizes or stabilizes at communities in one level of hierarchy. |
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L70.00268: Global and microstructural ergodic properties of financial markets Jack Sarkissian In finance everyone is concerned about future expectations. Whether it's pricing or risk evaluation - current models always involve some form of time averaging. Understanding the ergodic properties of the markets allows to replace the time average with ensemble average. Since calculation of ensemble average requires only one step in time, this approach allows much faster computation, and therefore a much faster reaction to changing market conditions. |
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L70.00269: Classical Dimer Model on the Square Bilayer Lattice Nisheeta Desai, Kedar Damle, Sumiran Pujari We study the Classical Dimer Model (CDM) on the square bilayer lattice with the fugacity of interlayer dimers as a tuning parameter. The square monolayer CDM is one of the paradigmatic model of a “Couloumb” phases whose distinct signatures are a) power law correlations in real space, and b) “pinch points” in the “transverse” form of structure factors in momentum space. Here we find that for low fugacity, the square bilayer CDM again hosts Coulomb phases with power law correlations. The pinch point phenomenology is however crucially different than the monolayer. This is integrally related to presence of longitudinal modes and Couloumb correlations together in the bilayer CDM ensemble. For high fugacity, it hosts a featureless phase with predominantly interlayer dimers and exponentially decaying correlations. Remarkably, even though the two phases are not symmetry related, numerical evidence from system sizes upto 512 × 512 points to a continuous transition rather than first-order. We provide an effective “electrostatic” description of the numerical data for low fugacities with the interlayer dimers interpreted as spontaneously fluctuating charged dipole defects. |
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L70.00270: Influence of correlated temporal disorder on an extinction phase transition Matthew Small, Alexander H Oniwa Wada, Thomas Vojta We employ large-scale Monte Carlo simulations to investigate the effect of long-range correlated temporal disorder (i.e. external noise) on extinction phase transitions in the logistic evolution equation. Uncorrelated temporal disorder is known to cause an unusual phase transition controlled by an infinite-noise critical point [1]. It features diverging density fluctuations at criticality, implying that the typical population decay is much faster than the ensemble average. Our results demonstrate that correlated temporal disorder enhances these effects; the correlations further accelerate the decay of a typical population while slowing the decay of the ensemble average. We also establish a relation to reflected fractional Brownian motion [2] which yields a conjecture for the critical behavior of the population. |
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L70.00271: Universal quantum Hawking evaporation of integrable two-dimensional solitons Charles Robson, Di Mauro Villari Leone, Fabio Biancalana In a work published in 1976, Abdus Salam and his student John Strathdee proposed a connection between two different fields, namely general relativity and the theory of nonlinear evolution equations. Their conjecture was simple: a black hole is nothing else than a soliton. We show that any soliton of an arbitrary two-dimensional integrable equation has the potential to evaporate and emit the analogue of Hawking radiation from black holes. From the AKNS matrix formulation of integrability, we show that it is possible to associate a real spacetime metric tensor which defines a curved surface, perceived by the classical and quantum fluctuations propagating on the soliton. By defining proper scalar invariants of the associated Riemannian geometry, and introducing the conformal anomaly, we are able to determine the Hawking temperatures and entropies of the fundamental solitons of the nonlinear Schrödinger, KdV and the sine-Gordon equations. The mechanism advanced here is simple, completely universal and can be applied to all integrable equations in two dimensions, and is easily applicable to a large class of black holes of any dimensionality, opening up totally new windows on the quantum mechanics of solitons and their deep connections with black hole physics. |
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L70.00272: Exotic quantum statistics from a many-body theory of Majorana fermions Joshuah Heath, Kevin Shawn Bedell Starting with a simple counting argument, we construct a statistical and thermodynamic model of free Majorana fermions at low temperature. Originally defined as a fermion identical to its own antiparticle state, Majorana particles often appear in the contemporary many-body literature as non-Abelian zero energy modes in topological superconductors. We deviate from the usual anyonic description and instead consider a gas of non-interacting, spin-1/2 Majorana fermions as Ettore Majorana first envisioned them. A combinatorial analysis of the many-body Majorana ensemble leads to a configurational entropy which deviates from the fermionic result with an increasing number of available microstates. A Majorana distribution function is derived which shows signatures of a sharply-defined Fermi surface at finite temperatures. The Majorana distribution is then re-derived in the context of a modified Kitaev chain with bosonic pair interaction. The thermodynamics of the free Majorana system is found to be nearly identical to that of a free Fermi gas, except now distinguished by a two-fold ground state degeneracy and, thus, a residual entropy at zero temperature. Experimental realization of the Majorana thermodynamics is then discussed in the context of real materials and cosmological phenomena. |
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L70.00273: BIOLOGICAL PHYSICS
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L70.00274: A numerical method for detecting and classifying multi-channel and multi-state binding events in single-molecule TIRFM experiments Joseph Tibbs, Elizabeth Boehm, Fletcher Bain, Colleen Caldwell, Todd Washington, Maria Spies, Ali Tabei Biomolecular binding may be observed using Total Internal Reflection Fluorescence Microscopy. By using multiple channels, which corresponds to different colors of fluorescence, the real-time interaction of multiple proteins can be observed. Although for many of these interactions the bound state is binary, for some the binding is more complex, with discrete states demonstrating intermediate levels of fluorescence. We will explain a numerical method for extracting these fluorescence traces from microscope data and then organizing and classifying traces from single-molecule experiments. With multiple channels and multiple binding states possible, the possible binding patterns are numerous. The data is organized in groups by these binding patterns and the statistics of each interaction is displayed. Which combinations are most likely, the binding duration of each protein or the probable binding/dissociation order of each subunit are all data which can inform on the underlying mechanism behind the interaction. We show how our method determines cooperative or inhibitory binding in multi-protein systems, or observe the construction of protein complexes. |
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L70.00275: Activity and Effects of Retroelements in Bacteria Davneet Kaur, Gloria Lee, Nicholas Sherer, Neil Kim, Elliot Urriola, Chi Xue, K. Michael Martini, Nigel Goldenfeld, Thomas Kuhlman Retroelements (RTEs) are abundant in eukaryotic genomes but less numerous in bacteria as group II introns. It has been hypothesized that eukaryotic spliceosomal introns and retrotransposons may have evolved as a result of invasion by bacterial group II introns. However, it remains unclear what limits RTE proliferation in bacteria and archaea and what enables it in eukaryotes. We quantify the effects of the human RTE LINE-1 and the bacterial group II intron Ll.LtrB in Escherichia coli, Bacillus subtilis and Enterococcus faecalis. We find that RTE expression is detrimental to all species, that LINE-1 successfully integrates into the chromosomes, and that the ability to repair DNA breaks with bacterial non-homologous end joining systems increases retrotransposition efficiency. Our results show that RTEs place a significant burden on organisms poorly equipped to handle their effects, and that the capacity of the last eukaryotic common ancestor for NHEJ may have enabled the proliferation of RTEs and the evolution of eukaryotes. |
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L70.00276: Understanding protamine-induced DNA folding in sperm Hilary Bediako, Adam D. Smith, Obinna Ukogu, Andrea Boskovic, Moumita Dasgupta, Ashley Carter We examine how protamine causes DNA folding within the sperm nucleus. Specifically, we are interested in how protamine loops the DNA into toroids that allow for tight packaging of the paternal genome. The formation of toroids have implications in epigenetics and fertility. Toroids may be formed in a single step (collapse model) or multistep (sequential model) manner. In the collapse model, all loops form along the DNA at once and then collapse into the toroid. In the sequential model, loops stack sequentially into a toroid. To decipher between these two models, we perform an in vitro Tethered Particle Motion (TPM) assay. In a TPM assay, an individual DNA molecule is attached to a bead and tethered to a cover-slip. By observing the position of the bead over time, we can measure the DNA length to a precision of about 10 nm and infer the folding trajectory of our DNA. We observe that as the length of the DNA increases, the number of folding events increases, suggesting that toroid formation is multistep (sequential model). If DNA folding is multistep, the location of nucleation loops is important as they may indicate where histones, and thus epigenetic tags, may be present. Moreover, the ratio of different protamine proteins may affect how toroids form and play a role in fertility. |
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L70.00277: Characterizing Protamine-Induced DNA Loop Formation Using a Tethered Particle Motion Assay Kyle Jones, Ashwin Balaji, Hilary Bediako, Andrea Boskovic, Ashley Carter Protamine is a protein found in sperm cells. It folds DNA into compact toroids by first forming it into loops and then stacking those loops. This compaction plays an important role in reproduction, ensuring that sperm are hydrodynamically efficient and protecting the DNA they carry. We use a tethered particle motion assay to examine the mechanics of loop formation in this process. By tracking the Brownian motion of a bead tethered to a length of DNA, we can detect changes in DNA conformation through changes in the bead's motion. We find that loop formation is a multi-step process with intermediate states. |
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L70.00278: Characterizing the Mechanism of DNA Loop Formation by Protamine Ashwin Balaji, Ashley Carter DNA compaction in sperm cells by the protein protamine represents an extreme case of polymer folding, approaching crystalline packing of the molecule. This high compaction is necessary for creating viable sperm, yet the physical mechanism of folding is unknown. In this study, we investigate how protamine folds DNA into a loop. One hypothesis is loop formation occurs through entropic folding where protamine binds and neutralizes the negative charge of the DNA backbone, increasing flexibility and allowing the molecule to fold into a loop. Another hypothesis is loop formation occurs as each protamine binds and bends DNA, changing its enthalpy. Using single-molecule force spectroscopy, we measure force-extension curves and fit them with a worm-like chain model. This model obtains the entropic and enthalpic portions of the folding, allowing us to differentiate between our two hypotheses. Specifically, we pull on DNA tethers biochemically attached on one end to a glass slide and on the other to a polystyrene bead. We then flow protamine over the tethers and measure the force-extension curve. We use a centrifuge force microscope to apply force and to image the tethers to track their extension. Here we report progress in building the instrument and measuring force-extension curves. |
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L70.00279: Expressing, Purifying, and Characterizing a Flavodoxin from the Solvent-Producing Clostridium Acetobutylicum Alyssa Alvarez, Andrea Padron, Anna Guseva, Jonathan Silberg Flavodoxins (Fld) are relatively small redox proteins responsible for facilitating the transport of electrons in certain types of bacteria and algae. In order to understand how these proteins control the flow of electrons between different redox partners in organisms with multiple electron transfer proteins, we must understand how their sequence and structure controls their partner specificity. While structures have been reported for Flds, we do not understand their structural properties sufficiently enough to predict electron flow in cells. |
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L70.00280: A three-dimensional analytical pathway to smoothly connect successive nucleosomes along DNA Seyed Ahmad Sabok-Sayr, Wilma K Olson Most DNA in the human genome is wrapped on nucleosomes. The nucleosome is an assembly of eight proteins and about 150 base pairs of DNA. Understanding the biological processing of DNA requires knowledge of how the nucleosomes are arranged in space. We have developed a new analytical model to describe the three-dimensional pathways of long stretches of nucleosome-bound DNA. Given the positions and orientations of a set of nucleosomes, we can find a smooth connector that joins the ends of successive nucleosomes along the DNA. Our studies show that the simplest equation which can smoothly connect any two nucleosomes is a quadric function which is uniquely determined by the position and orientation of each pair of successive nucleosomes. Since the equation for the connector only depends on the boundary conditions, our method can be used to connect either theoretical curves describing the nucleosomal pathway or the protein-bound DNA in known high-resolution structures. This treatment makes it possible to study the effect of elastic and electrostatic energies of the connectors on the stable structure of the nucleosomal arrays and to examine the influence of nucleosomal pathways, such as the length of bound DNA, on the global folding of the arrays. |
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L70.00281: Effects of Protein Conformation on Charge Regulation Jacob Palmerio, David Ross, George Thurston Proteins change charge in response to their electrostatic environments, by changing protonation patterns of titratable residues. This charge regulation is important for modeling protein interactions, including proteins that undergo conformational change, such as intrinsically disordered proteins, and enzymes that are allosterically controlled. We construct grand canonical partition function models that take account of flexibility by incorporating it into the relevant partition functions for each proton occupancy pattern. We use this model to analyze titration data for selected small molecule sequences, including dicarboxylic acids, diamines, and peptides. |
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L70.00282: Investigating Protamine-Induced Toroid Formation Andrea Boskovic, Kyle Jones, Hilary Bediako, Ashwin Balaji, Ashley Carter In somatic cells, DNA is folded by histones, forming chromatin. However, protamine, a small, arginine-rich protein that allows DNA to fold in mammalian sperm cells. Protamine allows DNA to form loops, which are then condensed into toroids that are stacked within the sperm cell. In order to investigate protamine-induced toroid formation in DNA, we performed a tethered particle motion (TPM) assay. Due to the fact that we see multiple states present in our visualizations of standard deviation over time, toroid formation in DNA due to the binding of protamine is a multi-step process. Understanding how DNA folds has applications in biomaterials, epigenetics and infertility. |
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L70.00283: Improved Molecular Dynamic Simulation of Protein Devices: PEGylated Proteins and Protein Microarrays Addison Smith, Thomas Knotts IV Protein-based devices have great potential to change how we harness the power of biology. PEGylated proteins and protein microarrays are two such devices. PEGylation covalently bonds polyethelyene glycol (PEG) chains onto a protein’s primary structure to increase a protein’s stability in the body. Protein microarrays covalently tether proteins onto a solid surface and has transformative applications for detection assays. However, for both devices, functionalization often renders it inactive. |
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L70.00284: Effect of substrate viscosity on stick-slip dynamics of migrating cells Rumi De Migration is central to many cellular processes such as wound healing, morphogenesis, embryonic development, tissue regeneration to name a few. 'Stick-slip' motion, observed during cell crawling, has been found to be strongly sensitive to the substrate stiffness. The stick-slip behaviour has been investigated before typically using purely elastic substrates. For a more realistic understanding of this phenomenon, we propose a theoretical model to study the dynamics on a viscoelastic substrate. Our model based on a reaction-diffusion framework, incorporates known important interactions such as retrograde flow of actin, myosin contractility, force dependent assembly and disassembly of focal adhesions coupled with cell-substrate interaction. We show that consideration of a viscoelastic substrate not only captures the usually observed stick-slip patterns, but also predicts the existence of an optimal substrate viscosity corresponding to a maximum traction force and minimum retrograde flow which was hitherto unexplored. Moreover, our theory predicts the evolution of individual bond force which provides insights into the stick-slip jumps on soft versus stiff substrates. Our analysis also elucidates the dependence of the duration of stick-slip cycles on various system parameters. |
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L70.00285: Actomyosin contractility depends on the load-dependent binding kinetics of myosin motors Pasha Tabatabai, Daniel S. Seara, Ian Linsmeier, Michael Murrell Within the cytoskeleton, myosin motor proteins consume chemical energy and generate mechanical work within the filamentous actin network essential for diverse cell functions like migration, division, and shape change. Myosin unbinding kinetics are force dependent- exhibiting “catch-bond” behavior which decreases the probability of unbinding under load. Altering the binding kinetics of proteins is prohibitively difficult, thus the impact of load dependent binding kinetics on the dynamics and mechanics of actomyosin contractility are unclear. To this end, we use coarse grained molecular dynamics simulations to explore the effect of catch bonds on the accumulation and dissipation of mechanical energy in the actomyosin cytoskeleton. We find that motor binding that increases under load sensitizes the network to myosin motor concentration, increasing the rate of contractility while simultaneously increasing network toughness, or the storage of mechanical energy. |
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L70.00286: Actin-microtubule co-formation inside of a giant unilamellar vesicle. Sungwoo Jung, C. H. Kim, A Setiawati, Huong Nguyen, M. C. Choi, Kwan Shin Microtubule and actin cytoskeletons are physically contacted in a cell, and dynamically coordinated to play vital roles in many cell functions, from migration, growth, and division. These structural dynamics of cytoskeletal proteins are of interest, the physical roles of cross-linking proteins between two filaments have been identified. Yet most studies were performed in a highly controlled interface or a bulk. Recently, we developed to simulate a cytoskeleton formation through ATP-dependent actin polymerization in a giant unilamellar vesicle. Optical stimulation initiated ATP synthesis and induced ATP-dependent actin polymerization, leading to growth of three-dimensional highly curled actin filament network. In this study, we further added the ingredients for microtubule formation into the actin polymerizable GUV system, and initiated the filament formations of those two cytoskeleton proteins simultaneously. We will discuss how these highly curled actin filaments in the single vesicle affects the structural environment in the presence of highly straight microtubule filaments. We will discuss how these two filaments are interacting in a highly confined, cell-like space where they are mutually restricted. |
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L70.00287: Building Towards Single Particle Characterization of Nanoparticle Bioconjugates Mohammad Abdul-Moqueet, Leeana Tovais, Kathryn Mayer Development of functional nanoparticle bioconjugates has been an important research area for nearly the last decade. Functionalized nanoparticles of various self-assembled monolayers (SAM-layers) have been used for biological and medical applications. Determining the exact spatial distribution of functionalized antibodies on the surface of the nanoparticles will provide necessary information to fully characterize and optimized nanoparticle bioconjugates for the preclinical stages of research. Gold bipyramids have been synthesized and then coated with a SAM-layer of various ligand types. Current and future work consists of conjugating these functionalized nanoparticles with fluorescently labeled anti-EGFR antibodies, which will enable imaging of the number and spatial arrangement of antibodies around the gold bipyramid using Total Internal Reflection Fluorescent (TIRF) Microscopy. EGFR is chosen as the target for future applications in cancer therapy. |
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L70.00288: Correlation of hatchling mass and egg volume in extant birds from Archilochus colubris to Struthio camelus Joshua Thomas, Scott Lee, Max Cooley, Richard Irving Observations suggest that birds hatch when they are near the maximum size that can be contained in their egg. In order to test this hypothesis, we have measured the volume of eggs of nineteen bird species from Archilochus colubris (the ruby-throated hummingbird) to Struthio camelus (the ostrich). The hatchling mass of these birds vary by more than three orders of magnitude. The volume of the eggs were measured by using scaled pictures of the eggs. The OpenCV library, and a custom python code was used to detect the edges of the eggs. We assumed the images were taken at right angles to the eggs, and that the eggs have cylindrical symmetry around the long axis. The points along the edges of the egg were fit with a polynomial to avoid resolution-induced calculation issues. The surface area and volume were calculated as if the points were a solid of revolution. Our method reproduces the volumes of ellipsoids with known dimensions with errors of less than 1%. The hatchling mass is found to depend on the egg volume via a power law with an exponent of 1.01 (standard deviation = 0.04), in support of the hypothesis. This relationship predicts a hatchling mass of 8.0 kg for the extinct Aepyornis maximus (the giant elephant bird), the largest known bird for which intact eggs exist. |
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L70.00289: Humeral bone strength and flight in eumaniraptoran dinosaurs Scott Lee, Joshua Thomas Flight requires that the animal be able to generate sufficient lift and thrust to support its weight in air. This requires that the humerus have a sufficiently strong section modulus to withstand the applied stresses. In order to study the possibility of flight in extinct dinosaurs, the humeral section modulus of 17 species of extant volant birds with masses ranging from 5.8 grams in Regulus calendula to 8.959 kg in Cygnus olor has been measured. The humeral section modulus is related to the mass of the animal via a power law with an exponent of 1.14 (standard deviation 0.02). The humeral section modulus is evaluated for 19 extinct dinosaurs from Dromaeosauridae, Troodontidae and Avialae. Comparing to the data for extant volant birds allows for the determination of those dinosaurs whose humeri were too weak to support powered flight. All five species of Avialae are found to have had humeri sufficiently strong for flight. Four dromaeosaurids (Microraptor gui, Graciliraptor lujiahunensis, Buitreraptor gonzalezorum, and Changyuraptor yangi) and one troodontid (Jianianhualong tengi) are also found to have had humeri that were strong enough for flight. This is a necessary, but not necessarily sufficient, condition for flight. |
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L70.00290: On the kinetics and dynamics of apatite crystallization at amyloid-solution interfaces found during enamel biomineralization Susrut Akkineni, Jinhui Tao, Stefan Habelitz, James J De Yoreo Mammalian enamel has a remarkable structure made of interwoven apatite filaments. Recent in vivo and in vitro evidence suggests amyloid-like amelogenin nanoribbons act as a scaffold for apatite growth1. However, the correlation between amyloid structure and apatite crystallization is unclear. Parts of this relationship are unraveled by the kinetics of calcium phosphate nucleation and growth at the amyloid-solution interface through in situ atomic force microscopy. Using peptide analogs of amelogenin, films of oriented nanoribbons with 3-fold symmetry stabilized by Van der Waal’s forces were self-assembled on graphite. They shared similar amyloidal properties even after addition of charged residues at C-terminus or with phosphorylated serine-16. Their role during apatite crystallization was then determined using physiologically-relevant solutions, favorable to heterogenous apatite nucleation. Quantitative analysis reveals that the peptide films, with or without additional charged residues, cannot independently promote apatite nucleation over time, but can provide an interface for growth of nuclei. |
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L70.00291: ABSTRACT WITHDRAWN
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L70.00292: Biomechanics of the peafowl’s crest reveals frequencies tuned to social displays Suzanne Kane, Daniel Van Beveren, Roslyn Dakin Feathers can act as vibrotactile sensors of mechanical stimuli during avian flight and tactile navigation, suggesting they may also detect stimuli during social displays. Here we present the first measurements of the biomechanical properties of bird feather head crests. We show that in Indian peafowl (Pavo cristatus), crest feathers are coupled to mechanosensory filoplume feathers. We also determined that peafowl crests are driven at resonance by their main social display frequency, but that other peacock feathers and crest of other birds have resonant frequencies that vary over a wide range (seven times that of the peafowl's crest). Peafowl crests were also driven to vibrate near resonance when we played back audio recordings of their displays in geometries that mimicked the acoustic near-field geometry found during these behaviors in vivo, but not when we played back control audio. These results suggest that mechanosensory stimuli could complement acoustic and visual perception and/or proprioception of social displays in peafowl and other bird species. |
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L70.00293: Mechanical principles of biofilm formation revealed by single-cell resolution imaging Jing Yan, Farzan Beroz, Howard A Stone, Ned Wingreen, Bonnie Bassler Biofilms are surface-associated bacterial communities embedded in an extracellular matrix. Biofilm cells are more resistant to antibiotics than their planktonic counterparts, which is a major problem in the context of chronic infections. We still lack a fundamental biophysical understanding of how bacteria, in time and space, build these three-dimensional structures that attach to surfaces and resist mechanical and chemical perturbations. During this talk, I will present a technique to image living, growing bacterial biofilms from single founder cells to ten thousand cells at single-cell resolution. Using the human pathogen Vibrio cholerae as a model biofilm former, we discovered that the biofilm develops from a disordered, two-dimensional layer of founder cells into a three-dimensional structure with a vertically aligned core. Using computer simulations, we found that verticalization proceeds through a series of localized mechanical instabilities on the cellular scale. By modulating cell lengths and osmotic conditions, we quantitatively tested the predictions made from the agent-based simulations. |
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L70.00294: Application of RLGC Models in Addressing Hospital Acquired Infections Jesus Perez, Yaw Obeng In this presentation, I will discuss the application of RLGC models to extract the electrical(RLGC) properties of modeled pathogens in the context of Hospital Acquired Infections (HAIs). HAIs can occur from antibiotic-resistant pathogen contaminants in either the medical procedures, devices, or from the overall hospital circumstance. It is known that exposure to UV light can prevent bacteria from reproducing. However, there is no reasonable quick-turn metrology for evaluating the efficacy of such treatments. Thus, our project is aimed at providing a module for acquiring the electrical properties of pertinent materials to help quantify the amount or intensity of UV light required kill bacteria. In our study, we investigated the changes in the capacitance and resistance of pertinent thin films in response to broad-band UV light irradiation. The results from this study demonstrate the feasibility of using our RLGC model to interpret the radio frequencies’ response of biological systems. |
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L70.00295: Myosin V executes steps of variable length via structurally constrained diffusion David Hathcock, Riina Tehver, Michael Hinczewski, Dave Thirumalai Myosin V is a molecular motor that performs intracellular transport by moving along actin filaments and generating energy through ATP hydrolysis. By alternating head detachment, myosin V steps hand-over-hand with the free head executing a random diffusive search for actin binding sites. Recent experiments suggest that the joint between the myosin lever-arms is not freely rotating, as indicated by previous studies, but instead has a preferred angle giving rise to structurally constrained diffusion. We address this controversy by developing a comprehensive model of myosin V, combining a polymeric description of the diffusive search with the kinetic network of states occupied during the stepping cycle. When the joint is constrained, our model predicts diffusion similar to that recently observed, allowing us to estimate bounds on the constraint energy. We also analyze the consistency of constrained diffusion with previous measurements of step distributions and the load dependence of the forward-to-backward step ratio, run length, and velocity, finding good agreement for each. The theory lets us address the biological significance of the constrained joint and provides testable predictions of new myosin behaviors, including a stomp distribution and the run length under off-axis force. |
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L70.00296: Label-free visualization of cellular uptake and trafficking of nanoparticles by interferometric scattering microscopy Jin-Sung Park, Il-Buem Lee, Hyeon-Min Moon, Kyoung-Hoon Kim, Seok-Cheol Hong, Minhaeng Cho Interferometric scattering (iSCAT) microscopy is a new label-free optical imaging technique, recently developed to identify the nano-sized particles beyond a diffraction limit at a high temporal resolution. Here we report on the direct iSCAT visualization for the moment of cellular uptake of nanoparticles which are diffused in the plasma membrane of a live cell. After initial docking onto the plasma membrane, nanoparticles undergo abnormal sub-diffusion, characterized by simple Brownian motion, local confined diffusion, or Hopf diffusion in their long trajectories. During these processes, we sometimes observed that the scattering signals from nanoparticles in the plasma membrane are suddenly disappeared after exhibiting the oscillating motion in the vertical direction of a flat membrane. Such signal loss indicates that these nanoparticles escape from the focal plane of the microscope as they transport rapidly into the cytoplasmic area after cellular uptake. Our experimental results demonstrate that the label-free iSCAT microscopy can be used as a powerful tool to shed interferometric light on dynamic biophysical processes of various intracellular phenomena. |
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L70.00297: The Effect of Intracellular Crowding on the Diffusion Dynamics of Neurofilaments and Microtubules Peter Jung, Nilaj Chakrabarty Neurofilaments are a class of cytoskeletal proteins which are essential for providing structural support for axons and for regulating axon diameter. Neurofilaments are primarily synthesized in the cell body of neurons and are cargoes of slow axonal transport. Several studies have established that neurofilaments are transported as assembled polymers along microtubule tracks driven by motor proteins. The transport kinetics of neurofilaments have been explained by a “Stop-and-go” model where neurofilaments move intermittently in a bidirectional manner. However, the established models do not take into account the intracellular crowding which can severely limit the diffusion kinetics and in turn affect the reaction rates. We model the neurofilament and microtubules as a bi-disperse population of hard disks in a circular domain representing the cross section of the axon. We find that both cellular confinement and steric repulsion play important roles in modulating the diffusion dynamics and in turn the reaction rates. We are also using our model to study whether phase transition effects at high crowding densities can explain the segregated neurofilament and microtubule populations typically found in some neurodegenerative diseases. |
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L70.00298: A Nonlinear Dynamical System Approach to Bird Song Analysis Xiao Zeng, Eve Armstrong, Vijay Balasubramanian Songbird vocal production is a complex nonlinear phenomenon. However, acoustic studies of bird vocalization have mostly been based on linear spectral analysis. Such analysis methods necessarily fail to capture the information content of song, and for that reason are not effective probes of the means by which songbirds communicate. We present a novel approach to the analysis and classification of songbird vocalization using nonlinear time series analysis techniques. Time-delay embedding is used to construct a new coordinate system in which to view the song time series. The number of coordinates required to unfold the dynamics represents the dimensionality of a new geometric space, wherein the song’s attractor can be visualized. We show that the reconstructed phase space representation of bird vocalization can reveal information that is absent in traditional linear approaches. |
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L70.00299: Spots to stripes: using machine learning to navigate pattern formation space Rebeckah K Fussell, Ayesha Bhikha, Suzanne Kane Current models of pattern formation (e.g., Turing reaction-diffusion theory) can generate many observed animal pigmentation patterns. However, their dependence on many interacting parameters makes it difficult to explore their full phase space of patterns. This is an important problem because research in cell signaling and developmental biology allows us to generate increasingly accurate pattern formation models. In this study, we first defined a “measure space” using 25 different measures of pattern geometry (e.g., feature circularity, compactness, intensity variance). We mapped photographs of pigment patterns in measure space and classified them using k-means clustering. We found that three measures were sufficient to group patterns into distinct classes (e.g., spots, stripes, labyrinthine, etc.) The next phase involves using this measure space as a guide for navigating the complex parameter space of a new pattern formation theory. For example, all known patterns generated by the model and a new test pattern (for which the model parameterization is unknown) first are mapped onto measure space. To determine the parameters needed to form the test pattern, a guided search can be performed in parameter space using the measure space distance between the test and known patterns. |
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L70.00300: Self-organized Pattern Formation in Bacterial Colonies Siyu Liu Pattern formation is ubiquitous in living organisms. In bacterial colonies, pattern formation generally relies on chemical signalings, such as in the case of chemotactic ring formation. Here we study how mechanical interactions between cells in a colony may promote self-organized pattern formation in bacterial colonies. The results may provide new insights into the development of structured bacterial communities, such as biofilms. |
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L70.00301: Building a Custom Microscope to Study Brownian Motion and Active Matter Hunter Seyforth, Wylie Ahmed Our goal is to build an optical microscope, calibrate it, and make precise measurements of Brownian motion and diffusion using multiple approaches such as mean squared displacement (MSD) analysis and differential dynamic microscopy (DDM). These methods of analysis were applied to quantify the motility of active matter and standardize the process to develop an advanced module for the graduate program. We constructed a microscope based on the design by Kemp et al.(arXiv:1606.03052). Then, the Brownian motion of 1 micron colloidal particles were studied and both single particle tracking and image correlation techniques were implemented to analyze colloidal diffusion. To do this, publicly available matlab codes for particle tracking, MSD analysis, and DDM analysis were applied to calculate the diffusion coefficient. These methods were utilized to quantify the diffusion of two different types of active matter: janus particles and swimming microorganisms. This was done to quantify the motility of active matter. This project is being developed into an advanced lab module to be an introduction to physics research, fortify concepts from optics and statistical physics, and give students experience in building optical systems and analyzing noisy data. |
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L70.00302: Analysis and Modeling of Mitochondrial Fission and Fusion Processes in Cells From Healthy and Trisomy Patients Johanna Paine, Carlos Perez, Ghanim Ullah, Jorge Busciglio Mitochondria play a vital role in many cell functions, including ATP production, modulation of Ca2+ signaling and apoptosis. The homeostasis of the fission and fusion of the mitochondrial network allow for healthy cellular function. If the homeostasis of fission and fusion processes becomes unbalanced, the mitochondria can no longer supply enough ATP nor process the calcium ions which leads to apoptosis. Mitochondria's role in apoptosis makes it a possible target for curing neurodegenerative diseases . The causes behind the progressive degeneration of neurons are not yet understood, beyond a correlation with age, an understanding of the details of mitochondrial function and structure is crucial for better treatments for neurodegenerative diseases. Mitochondrial reticulum structure and function are altered due to conditions like Trisomy 21. We investigate the difference rates of fission and fusion, cluster size and mean degree of healthy and Trisomy mitochondria reticulum. We present a model of the dynamic mitochondrial reticulum, and deduce fission and fusion rates from a single image. This process can be used to deduced the fission and fusion rates of mitochondrial networks with different neurological disease to understand the exact mechanisms these diseases. |
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L70.00303: Time cells in the mouse dentate gyrus: An apparent instance of traveling waves in the brain Wei Zhong Goh, Marc Howard The role of standing brain rhythms in cognition has been well investigated, but traveling waves have only recently attracted interest for their potential role in memory and attention. A manifestation of traveling waves in the brain may be "time cells". In animal experiments, a task-relevant event triggers a reliable sequence of neural firing. Each "time cell" fires during a circumscribed period of a delay interval; different events can trigger different sequences. As the time interval since the event increases, the proportion of active time cells decreases. We present evidence of time cells in the mouse dentate gyrus whose activity spans a 20 s delay interval. We describe how information encoded about the time interval since the event is characteristic of a propagating wave traveling in a medium with graduated index of refraction. This framework allows us to characterise how the brain is continually aware of its orientation with respect to events in the world unfolding in time. |
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L70.00304: Modularity and flexibility quantify unique processing of music and speech stimuli in the human brain Melia Bonomo, Christof Karmonik, J Todd Frazier, Michael Deem Music has been shown to have therapeutic benefits for mental health, though few studies have quantified the impact on the brain. We investigated neural network changes from fMRI data while subjects actively listened to a variety of auditory pieces that varied in cultural familiarity and emotivity. We applied theory derived in our group showing that the extent to which modularity and flexibility of the network are selected for depends on the complexity and timescale of the activity being carried out. We found a strong negative correlation between modularity and flexibility while subjects listened to speech; this relationship decreased during self-selected and culturally familiar music, and it became random during culturally unfamiliar music and speech. We also found that modularity during a self-selected song was predictive of the neural network architecture during other pieces. These novel quantifiers of neural activity pave the way for creating individualized predictions of response to music engagement and tailoring therapy interventions to individual patients. |
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L70.00305: Modelling Axon Growth Using Driven Diffusion Nima Dehmamy, Yanchen Liu Axon growth has been studied at small scales using models based on diffusion. |
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L70.00306: Overcome Competitive Exclusion in Ecosystems Xin Wang, Yang-Yu Liu Explaining biodiversity in nature is a fundamental problem in ecology. An outstanding challenge is embodied in the so-called Competitive Exclusion Principle: two species competing for one limiting resource cannot coexist at constant population densities, or more generally, the number of consumer species in steady coexistence cannot exceed that of resources. The fact that competitive exclusion is rarely observed in natural ecosystems has not been fully understood. Here we show that by forming chasing triplets among the consumers and resources in the predation process, the Competitive Exclusion Principle can be naturally violated. Our model can be broadly applicable to explain the biodiversity of many consumer-resource ecosystems and deepen our understanding of biodiversity in nature. |
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L70.00307: A chemical basis for metabolic cooperation in microbial communities Akshit Goyal, Sandeep Krishna What distinguishes autonomous and cooperating metabolic networks in microbes? How does the underlying universal chemical network constrain metabolic cooperation between individuals? Answering these questions remains a conceptual roadblock given the dearth of culturable, sequenced microorganisms: only about 1% of the expected diversity. Here, we attempt to sidestep this experimental limitation by algorithmically generating reaction networks from the repertoire of chemical reactions in KEGG. We generate a large set of reaction networks, both autonomous and cooperating (cross-feeding). We survey their size, energy (ATP) and biomass yields, as well as their response to a variety of perturbations. We find that while rare, cross-fed pairs can best even the most productive autonomous networks without an obvious compromise to stability. This central result is robust to changing environmental conditions, biomass compositions and the precise method to calculate yields. As a proof-of-concept that a “productivity boost” is possible by cross-feeding, our study provides a chemical basis for the prevalence of metabolic diversity and cooperation in naturally-occurring microbial communities. |
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L70.00308: Heterogeneous Absorption of Antimicrobial Peptide LL37 in Escherichia coli Cells Enhances Population Survivability Paul Talledo, Mehdi Snoussi, Nathan Del Rosario, Bae-Yeun Ha, Andrej Kosmrlj, Sattar Taheri-Araghi Antimicrobial peptides (AMPs) are broad-spectrum antibiotics that selectively target bacteria. Here, I present our recent investigations on the activity of human AMP LL37 against Escherichia coli by integrating quantitative, population and single-cell level experiments with theoretical modeling. Our data indicate an unexpected, rapid absorption and retention of a large number of LL37 by E. coli cells upon the inhibition of their growth, which increases the chance of survival for the rest of the population. Cultures with relatively high cell density exhibit two distinct subpopulations: a non-growing population that absorb peptides and a growing population that survives attributable to the sequestration of the AMPs by other cells. Comparatively, we screened several common antibiotics for their MIC as controls to juxtapose AMPs' effects on E. coli. A mathematical model based on this binary picture reproduces a quite surprising behavior of E. coli culture in the presence of LL37, including the increase of the MIC with cell density—even in dilute cultures—and the extended lag duration of growth introduced by sub-lethal dosages of LL37. |
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L70.00309: Survival chances of a prey swarm: selfish runaway versus cooperative interaction Rumi De Cohesive group formation has been observed in diverse species, for example, flock of birds, school of fishes, herd of zebras, huddle of penguins to name a few. In nature, swarming behaviour has generally been found in search of food, for breeding, or to avoid predators etc. However, swarming could also thought to be unfavourable for preys as the predator could easily track and attack the whole group. Here, we investigate the effect of cooperative interaction within a prey group based on a simple theoretical prey-predator model framework incorporating short range repulsion and long range attraction between preys. Moreover, the range of interaction of preys, as in real scenario, may be limited due to their sensitivity, vision, age, or even physical structure; hence, in our model, we consider that each prey interacts with other neighbouring preys within a certain range of interaction radius. Our analysis shows that varying range of interaction vastly influences the trajectory of preys when chased by a predator and also strongly affects the survival probability of the prey group. Interestingly, we find that the survival of number of preys increases within an intermediate regime of interaction radius. These findings could also be qualitatively mapped with observations in nature. |
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L70.00310: Consecutive seeding and transfer of genetic diversity in metastasis Alexander Heyde, Johannes Reiter, Martin A Nowak The transfer of genetic diversity between spatially separated growing populations is relevant to a wide range of biological applications, including clonal diversity in cancer metastasis, clonal hematopoiesis in stem cell biology, and species diversity in ecology. We study a multitype branching process of population growth that originates from a single individual but over time receives additional migrants. We derive a surprisingly simple expression for the fraction of genetic diversity transferred between populations as a function of the immigration rates that connect them. Additionally, we calculate statistics for the fixation index FST between populations. Using this model framework, we analyze single-cell sequencing data from ovarian, breast, and colorectal cancer samples collected from 15 patients. For these genetically diverse cell populations, we find an average seeding rate of 1-10 migrant cells per cellular generation time. Under typical metastasis growth conditions, this estimate suggests that 16-130 cells seeded each metastasis and left surviving lineages. Since primary tumors are often surgically removed, the genetic diversity of these metastases determines the probability for treatment efficacy. |
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L70.00311: Tracking motion and sleep in Astyanax fish Adam Patch, Yaouen F Fily Astyanax or tetra fish, as a genus, contain more than 150 species, many of which have migrated into coastal caves around the Gulf of Mexico, convergently evolving sleeplessness, blindness and more sensitive lateral lines. Social behavior is also affected, which may in turn affect sleep patterns. We analyze Astyanax tracking data from the labs of Alex Keene and Erik Duboué at Florida Atlantic University and Wilkes Honors College to characterize motion and sleep patterns and their variations across species. |
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L70.00312: Directed self-organization through thermoregulation in ant colonies Fazil Uslu, Sean McGregor, Laurent Keller, Mahmut Selman Sakar The nest of social insects is a complex architecture housing a multitude of individuals in a highly structured hierarchical network. At the heart of each of these spontaneously organized colonies, are the brood. Given the great lengths that social insects invest in their nest design and the spatial fidelity that individuals present, it stands to reason that the location of brood may regulate the dynamics of the social network and in turn, influence division of labor. We aim to test this prediction in colonies of C. fellah by taking advantage of the inherent thermosensitivity of the colony members. We discovered that the workers repeatedly transport the brood to locations within a certain temperature range. We then developed a robotic heat regulation system that allows us, for the first time, to directly control the position of the brood pile within an ant colony by subtly altering fine thermal gradients under the nest surface floor, while simultaneously, gathering precise behavioral data for all individuals within the colony using automated visual tracking. Analysis of spatial and social interaction network reveals novel insight on how spatial reorganization within the colony drives changes in population dynamics and collective decision making. |
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L70.00313: Morphology of interacting proteins (CorA) by a coarse-grained Monte Carlo simulation Warin Jetsadawisut, Sunan Kitjaruwankul, Panisak Boonamnaj, Pornthep Sompornpisut, Ras Pandey A transmembrane protein such as CorA performs selective transport of magnesium across the membrane with specific functions of its inner (iCorA) and outer (oCorA) membrane segments and known to exist as a homo-pentamer. The thermal response of iCorA is found [1, 2] to differ from that of oCorA in both native and denatured phases. Self-organized structures of proteins (CorA and iCorA) are examined by a coarse-grained model as a function of protein concentration at a range of temperatures. The collective structures show clear distinctions in morphology visually in its dilute concentration from that in the crowded (dense) protein matrix both at low and high temperatures. The effective dimension D of CorA assembly is found to be lower (D £ 2) than that of iCorA segments which remain globular (D ~ 3) at almost all length scales in its native phase. Based on the higher structural response, (i.e. structure factor and radius of gyration) in its native phase, the inner-segments may be more conducive to transient channel pathways due to cooperative protein-protein interactions. |
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L70.00314: Exploring the structure of single amylose chains using molecular dynamics Mason Sullivan, Mohammad Hassan Khatami, Hendrick W de Haan Amylose is a polymeric chain consisting of glucose molecules bound through α-1,4 glycosidic linkages. Amylose can assume a variety of conformations in water – the structure and dynamics of which are of primary interest in this research. Despite well-defined secondary structures of amylose chains in experimental studies, the structures obtained through MD simulations lack such well-defined conformations (ie. helical structures). Presented are results from all-atom MD simulations of single amylose chains (V-amylose) in water. From these simulations, criteria for helix-like structures is developed and the prevalence of these structures is explored. Dynamics such as bond flipping and other structural changes and their effects on helices are also discussed. |
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L70.00315: Growing Glucose-based Carbohydrate Nanoparticles using Molecular Dynamics Simulations Mohammad Hassan Khatami, Hendrick W de Haan PhytoSpherixTM is a dendritic, biodegradable carbohydrate-based nanoparticle, produced by Mirexus Biotechnologies from sweet corn. This particle consists of roughly 22,000 glucose units, with an overall experimental radius of ~17 nm, which acts as a form of energy storage in plants. Despite the extensive experimental studies, the detailed structure of this particle is unknown. In this work, we employ large-scale molecular dynamics simulations to construct the structures of PhytoSpherix-like particles in atomistic details. Here, we start with an initial glucose seed and grow our structure in dendritic fashion in the presence of explicit water molecules, while the structure is simulated using the GROMACS package. We built up to ~5000 glucose unit particle (~25% of the actual size), where the simulation box contains more than 5 million atoms. Details of the structure in the form of the radial density of the particle are provided. We use our structures to study the interactions and dynamics of the PhytoSpherix particle. |
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L70.00316: Computer simulation model for aggregration in a multi protein model system Ian MacKay, Apichart Linhananta, Robert Girardin Protein misfolding and aggregation is believed to be associated with diseases such as Alzheimer’s Disease, Huntington’s Disease, ALS and others. Healthy proteins typically function in their folded collapsed structure (native state) but in certain cases they unfold into strands and beta sheets, which then aggregate into larger fibrils and plaques. To analyze this behaviour, we have developed a computer simulation model using discontinuous molecular dynamics on a system of Trp cage proteins. The Trp cage is a small (20 residue, 189 atoms) protein known to fold quickly and therefore is suitable for computer simulation. Previous work (Linhananta, Boer, Mackay J Chem Phys 122, 114901. 2005) modeled the Trp Cage with the all atom Go model for atom-atom pair interaction potential within a single protein. We expand on this previous work by incorporating the Go potential for atom-atom pairs between separate proteins. We observe destabilization and unfolding due to perturbation by neighbouring proteins and analyze the aggregation behaviour at various concentrations and temperatures. Transition state analysis shows the folding/unfolding transition is less cooperative than for the single protein system. |
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L70.00317: Active wrinkles to drive self-cleaning: A strategy for anti-thrombotic surfaces Luka Pocivavsek, Joeseph Pugar, Edith Tzeng, William Wagner, Sang-Ho Ye, Enrique Cerda, Sachin Velankar The inner surfaces of arteries and veins are naturally anti-thrombogenic, whereas synthetic materials placed in blood contact commonly experience thrombotic deposition that can lead to device failure or clinical complications. Presented here is a bioinspired strategy for self-cleaning anti-thrombotic surfaces using actuating surface topography. For the specific application of prosthetic vascular grafts, the potential of using pulse pressure, i.e. the continual variation of blood pressure between systole and diastole, to drive topographic actuation was investigated. Soft cylindrical tubes with a luminal surface that transitioned between smooth and wrinkled states were constructed. Upon exposure to blood under continual pressure pulsation, these cylindrical tubes also showed reduced platelet deposition versus control samples under the same fluctuating pressure conditions. We speculate that the observed thrombo-resistance behavior is attributable to a biofilm delamination process in which the bending energy within the biofilm overcomes interfacial adhesion. This novel physical strategy to reduce thrombotic deposition may be applicable to several types of medical devices placed into the circulatory system, particularly vascular grafts. |
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L70.00318: Behaviour of an oscillating chiral squirmer in a chemical gradient RUMA MAITY, P. SEKHAR BURADA The rotational motion in addition to translation is an advantage of the chiral squirmer over a simple squirmer in such a way that the chiral one can change its orientation in any arbitrary direction. This is an important property required by the body to chemotax which is nothing but the directional movement of it in response to the chemical gradient. The chiral squirmer considered here performs an oscillatory motion in the medium which can be captured with the aid of a time-dependent surface slip velocity [1]. In presence of the gradient, the restricted oscillatory motion of the squirmer is altered due to the modification in the slip coefficients of the slip velocity and it starts to move towards the direction of the gradient. Here we have studied, how the net displacement of the body at the end of a complete cycle of oscillation towards the direction of the gradient depends on the strength of the gradient and the frequency of oscillation. This study can be helpful to design an artificial oscillating swimmer which is capable to chemotax. |
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L70.00319: Collective dynamics of 2D self-propelled semiflexible chains GIMOON NAM, Changbong Hyeon Collective behavior is an emergent dynamics in active systems. This behavior often involves a hydrodynamic transition between coherent and turbulent flows, which occurs spontaneously even in the absence of an external driving. While the coherent flow state is theoretically well described as a polar and nematic phase, the turbulent state is rather difficult to describe as a single phase due to the existence of many complex local structural patterns such as vortices and spirals. So far, most of the studies have focused on such transition in self-propelled particles system, but the corresponding polymers system is rarely studied. In recent simulation studies on self-propelled chains, it has been implicated that the transition could take place near the boundary between the coherent flow and spiral phases, where each phase is characterized by different values of the stiffness and Peclet number of a single chain. To reveal the underlying mechanism, we have studied the collective dynamics of 2D active semiflexible chains. By means of coarse-grained modeling and Brownian Dynamics simulation, we modeled self-propelled chains melt and monitored its structural dynamics. In this poster session, we report our recent progress on the collective behaviors of 2D active polymer system. |
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L70.00320: Compressing a Swarm of Multicellular Magnetotactic Bacteria with an Applied Magnetic Field Alejandra Rosselli, Cameron Mitchell, Benjamin Roque, Alexander Petroff Bacteria of the species Magnetoglobus multicellularis live in spherical colonies composed of 10-50 individual bacteria. The colony swims as a single unit parallel to the Earth’s magnetic field. Here we investigate the collective dynamics of a swarm of these colonies under an applied magnetic field. We orient the magnetic field towards a wall and measure the spatial distribution of the colonies. We track the motion of individual colonies as they align with the field and collide with one another and the chamber walls. We show that the distribution of colonies is the same as that of an ideal gas in a harmonic potential. We present a simple model to explain how this similarity arises and how it breaks down. |
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L70.00321: Control of Multicellular Magnetotactic Bacteria with a Magnetic Field Benjamin Roque, Alejandra Rosselli, Cameron Mitchell, Alexander Petroff Bacteria of the species Magnetoglobus multicellularis form spherical colonies composed of tens of cells. A colony moves as a single unit as each cell rotates its flagella. Magnetic minerals within each cell cause the direction of the colony’s motion to align with the ambient magnetic field. Here we characterize the motion of these large, fast-swimming colonies both individually and collectively in an oscillating magnetic field. First, we observe the dynamics of individual colonies. We measure their swimming speed, magnetic moment, and diffusion coefficient. |
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L70.00322: Mechanism of Reentrant Liquid Condensation in Arginine-rich Low Complexity Domains Taranpreet Kaur, Ibraheem Alshareedah, Priya R. Banerjee Arginine-rich (R-rich) low complexity domains (LCDs) are ubiquitous in eukaryotic RNA binding proteome, act as multi-valent RNA/protein-binding elements for liquid-liquid phase separation, and implicated in c9orf72-related ALS disease etiology. Recently, we showed that RNA mediates a remarkable reentrant liquid condensation of R-rich LCDs1, a phenomenon that is also observed in the cell2. Combining biophysical experiments and polymer physics theories, here we study the mechanism of the reentrant phase behavior of R-rich LCDs in ALS-associated protein FUS. We show that charge regulated electrostatic forces (long range) control condensation and de-condensation thresholds, whereas short-range attractions determine the stability of the condensates. Importantly, conditions promoting homotypic LCD-LCD and/or RNA-RNA interactions result in a more complex phase behavior, such as the formation of distinctive condensates with orthogonal physical properties. Together, our experiments and free-energy surface modeling suggest a highly tunable phase behavior of R-rich LCDs. |
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L70.00323: Modularity Promotes Adaptation in a Model of Exploratory Evolution Shubham Tripathi, Michael Deem Biological systems are modular. They are composed of distinct components that function almost independently of one another. Studies have shown that modularity can spontaneously emerge in systems evolving under changing environmental conditions if the goals of evolution are varying in a modular manner or if horizontal gene transfer is present. Here, we examine a model that relaxes these constraints. We analyzed the effect of adding modular organization to a previously characterized model of evolution in gene regulatory networks. In this model, the topology of regulatory interactions is fixed while the regulatory strengths evolve to satisfy a linear constraint on the levels of different regulatory factors. We observed that the probability of successful adaptation within a fixed time period was higher when the regulatory topology was modular. The probability varied non-monotonically with the modularity of the regulatory topology. There are neither modularly-varying goals nor horizontal gene transfer in our model. Our model thus represents a previously uncharacterized scenario wherein modularity can be beneficial in evolving biological systems. |
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L70.00324: Bio-energy Transport as a Dressed Vibrational Exciton in Protein Molecules Peighton Bolt, Theja De Silva Following the ideas of Davydov's soliton theory, we study the bio-energy transport in protein molecules. By using a quantum Brownian motion model for a phonon dressed vibrational exciton, we calculate the time-dependence on the mean square distance, diffusion coefficient, and energy of the vibrational exciton. We find the time-dependence by solving the quantum Langevin equation and find oscillatory behaviors due to the super-diffusive non-ohmic dissipation. We find that the vibrational exciton gains an overall energy due to the coupling to the phonon bath, it also dissipates its energy to the environment as it propagates. The amount of energy gain and the oscillatory features depend on both temperature and the phonon-vibron coupling. |
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L70.00325: Continue study of nano-Co synthesized by pea (Pisum Sativum L.) and lucerne (Medicago Sativa L.). Nereida Avendaño Gavira, Elizabeth Chavira, Guadalupe Zavala, Adriana Tejeda Our research group reports the synthesis on nano-Co using; Co3O4 (STREM CHEMICALS) reagent, analyzed by X-ray powder diffraction, (XRD) with concerning a hexagonal unit cell (PDF 43-1003) and 3% of iron oxides (PDF: 8-0097) impurities. |
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L70.00326: Nanocrystals of silver reaction in a medium with microalgae Rubi Vazquez Mora, Elizabeth Chavira, Yoxkin Estevez, Adriana Tejeda, Omar Novelo, Josué Romero Ibarra, Karla Eriseth Morales
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L70.00327: Identification of a Model Organism for Giardia Lamblia by Raman Spectroscopy Josemaria Soriano, Chenglong Zhao, Farzia Karim Giardia Lamblia is a protozoan parasite which causes Giardiasis, the most common intestinal protozoan infection in the world. Several studies show the presence of blackish pigment granules in retinal layers due to Giardiasis, making of Giardia a pigment-related parasite. In the following work, Raman spectroscopy will be used for the identification of Euglena gracilis, model organism chosen because of its physical similarity, low cost and biosafety. In this study, Euglena samples were excited at 785 nm and signal optimization was performed using Surface-Enhanced Raman spectroscopy (SERS) utilizing gold (Au) nanoparticles as substrate. Our results indicate that SERS provides a four-fold signal enhancement for peaks at 1188 cm-1 and 1530 cm-1, corresponding to the β-carotene conjugated double-bond system present in Euglena, pigment concentrated in the light sensitive eyespot. Thus, we have shown the effectiveness of Raman and SERS Spectroscopy on the identifying of microbial pigments, constituting a robust method to detect and characterize pathogenic microbes such as Giardia, which will have significant downstream diagnostic implications. |
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L70.00328: Single Molecule Localization and Orientation Mapping Using a Joint Inversion Technique Anthony Mautino, Abhishek Kumar, James M Marr, Mark McLean, Stephan Stranick, Veronika Szalai, James Liddle For rotationally-constrained molecules, single molecule (SM) localization based super-resolution imaging can incur losses in accuracy when not accounting for the effect of SM orientation on the point spread function. It is important to determine molecular orientation both to maximize localization accuracy and also because orientation provides information about the local molecular environment, which determines features such as chemical reactivity, biomolecular interactions, local polymer mobility, etc. To map the 3D orientation of SMs, we collect the intensity projected onto four different polarization orientations simultaneously and use the intensities in the different channels to reconstruct each dipole’s 3D orientation. These data provide 1) information on the SM’s local environment, and 2) constraints for image point spread function-fitting and localization. SM images acquired from a second objective positioned on the opposite side of the sample versus the four-channel collection system are utilized for a joint inversion technique for position. We present techniques of registration, localization, and polarization analysis, along with an uncertainty analysis and assessment of the developed methods. |
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L70.00329: Mechanisms of phosphorylation spreading by kinases Mec1 and Tel1 after a DNA double strand break in budding yeast Kevin Li, Jane Kondev One of the hallmarks of DNA damage is the rapid phosphorylation of H2A histones near the site of a DNA double-strand break, extending out to ~50 kb from the break site. The phosphorylated H2A, known as γ-H2AX, plays a role in the recruitment and retention of DNA repair factors. In budding yeast, the kinases Mec1 and Tel1 are responsible for phosphorylating H2A histones, but it is not known how the kinases spread from the break site to the distant H2A’s. |
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L70.00330: Mechanics of Zn modified fibrin network JING XIA, Fred C. MacKintosh, Liheng Cai, Huayin Wu, David A Weitz Fibrin are the main constituent during the hemostasis due to its unique mechanical properties resulting from its hierarchy structure, malfunction of fibrin can lead to diseases such as thrombosis. Here we show Zn can tune the fibrin network and its mechanical properties. In the presence of Zn2+, fibrin protofibrils form huge fiber bundles which are intrinsic loosely coupled. By further comparing with theoretical model, we show that under low stress, the mechanical properties of Zn modified fibrin network are contributed by the thermal fluctuation of the network; at high stress, the mechanical properties are contributed by single protofibril mechanics. |
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L70.00331: LiveFISH: Visualizing endogenous RNA in living cells Takuma Inoue RNA takes part in genome regulation dynamically in living cells. However, studying RNA molecules in action is difficult. Here we present a technique by which endogenous RNA molecules may be visualized directly in living mammalian cells. Our approach (liveFISH), based on fluorescence in situ hybridization (FISH) but extended to work in living cells, overcomes previous limitations, and is capable of labeling arbitrary species of endogenous RNA without need for genetic modification. |
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L70.00332: Assessment of active vesicle membrane fluctuations Kisung Lee, Hyun-Sook Jang, Steve Granick Non-equilibrium fluctuations of giant unilamellar vesicles (GUV) are detected using laser interferometry. Protein driven active membrane fluctuations are resolved with exceptional resolution in a broad frequency range (0.1 Hz – 1000 Hz) and sub-nm resolution. This yields a deeper assessment into the non-equilibrium mechanics of GUV membranes. |
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L70.00333: A Comparison of Atomistic and Coarse-Grain MD Simulations Through Local Stress Analysis of Lipid Bilayers Conner Winkeljohn, Juan Vanegas Understanding the mechanical properties of lipid membranes is very important for many biological functions including membrane fusion, transport, and mechanosensation. One can characterize the mechanical state of a lipid bilayer through lateral stress or pressure profiles, which are uniquely sensitive to molecular features, obtained from molecular dynamic (MD) simulations. Lateral pressure profiles may be used to obtain various elastic constants by means of the integral moments. We analyze MD simulations of lipid bilayers of the commonly used phospholipids POPC and DPPC, and show that lateral pressure profiles are also largely sensitive to force-field parametrization in atomistic and coarse-grained models. We compare the atomistic force fields CHARMM36 and GROMOS 43A1-S3, as well as the coarse-grained force fields Martini, Polar Martini, Dry-Martini, and BMW-Martini. We further characterize the individual contributions of the interatomic potentials (i.e., VdW, coulomb, angles, et.) to the overall lateral pressure to better understand the internal balance of forces within the membrane. Our analysis shows an unexpected result that the lateral pressure profile from the atomistic CHARMM36 membrane closely resembles the profile of the solvent-free Dry-Martini force-field. |
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L70.00334: The Effect of Microtubule-Associated Protein Tau on Polymerization of Cancer Microtubules Jane Breslin, Mitra Shojania Feizabadi One of the cellular microtubule-associated proteins (MAPs), Tau protein, can regulate the polymerization of microtubules. The effect of Tau protein, which is known as a neuronal MAP, on neuronal microtubules have been well studied. This protein has the stabilizing effect on polymerization of neuronal microtubules and therefore, enhances their polymerization. Tau protein has also been observed in some cancer cells such as human breast cancer cells. In this study the in vitro effect of Tau protein on polymerization of breast cancer microtubules will be discussed and compared with the one obtained from brain microtubules. Our results indicate that in contrast with the stabilizing effect of tau protein on the polymerization of neuronal microtubules, breast cancer microtubules in vitro do not display promoted polymerization behavior. In contrast with the structure of neuronal microtubules, human breast cancer microtubules consist of different beta tubulin isotype distributions. In addition, Tau proteins interact with beta tubulins. Collectively, the observed distinct polymerization behavior observed may possibly be associated to the way that Tau protein interacts with different beta tubulin isotypes. |
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L70.00335: Quantifying Polarization Factor of MCF7 microtubules in the presence of Tau Protein. Ibukunoluwa Akintola, Marcos Velasco Hernandez, Mitra Shojania Feizabadi Microtubules are one of the intracellular components that consist of alpha and beta tubulin. The C-terminal tails of tubulin carry some negative electric charges, therefore, polymerized microtubules are negatively charged. The dielectric specifications of neuronal microtubules have been evaluated in several reported studies. However, our knowledge about dielectric factors of non-neuronal microtubules is still limited. |
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L70.00336: Effects of Confinement and Crosslinking on the Organization of Actin Networks Oghosa Akenuwa, Steven Abel The actin cytoskeleton is vital to cellular processes such as the molecular motor-driven transport of organelles within cells. Crosslinking proteins organize actin filaments into bundles, affecting the local and global architecture of the actin filament network and influencing intracellular transport. In plant cells, the actin cytoskeleton is vital for bulk, cellular-scale transport known as cytoplasmic streaming. However, much remains unknown about how confinement and crosslinking by proteins such as plant villin influence cytoskeletal organization and intracellular transport in plant cells. In this work, we use hybrid computational methods utilizing kinetic Monte Carlo and Brownian dynamics simulations to study the organization of actin networks as a function of system size, system shape, and density of crosslinking proteins. Using tools from graph theory, we gain insight into cytoskeletal architecture by analyzing graphs characterizing the connectivity of actin networks. Finally, we examine the influence of resulting network structures on dynamics of molecular motor motion. |
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L70.00337: Sol-gel transition in the actin cytoskeleton Carlos Bueno, James Liman, Yossi Eliaz, Herbert Levine, Margaret Cheung, Peter Wolynes The actin cytoskeleton contains numerous actin binding proteins that are able to regulate its dynamic behavior. This dynamic behavior is mainly controlled by actin treadmilling and motor walking, but it can also be influenced by other proteins such as cross-linker and branchers. In this work we use ordinary differential equations and stochastic mechanochemical simulations to model how three different actin binding proteins: non-muscle myosin IIA (NMIIA), α-actinin, and Arp2/3 bind to actin filaments. Then we analyze how the connectivity, as described by the Flory-Stockmayer theory, changes as a function of the concentration of the actin binding proteins on both models. We find that the sol-gel transition in the system occurs at lower concentrations of linker and motors than those required to observe contractions in the mechanochemical simulations. Finally we compare this result with actin networks containing Arp2/3. We expect our results to give an insight into how the connectivity of the network affects its dynamic behavior. |
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L70.00338: Single Wall Carbon Nanotube (SWCNT) as an Intracellular Gene Delivery Cargo ADEYINKA ADESINA A SWCNT is truly one-dimensional nanoscale object, possessing unique optical, electronic, and mechanical properties. Earlier works on SWCNT toxicity and size allowed for widespread use of SWCNTs in biological studies. SWCNTs bind to biomolecules, proteins and nucleic acids via Coulomb and other interactions, both on the specific and nonspecific level, this motivated many drug and gene delivery studies which demonstrated that SWCNTs, functionalized with polymers and biological molecules may serve as highly efficient and easily targeted delivery agents. |
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L70.00339: Mining recombination algorithms in modular biosynthetic gene clusters Zhiyuan Li, Donia Mohamed Non-ribosomal peptide synthetases (NPRS) are ubiquitous in micro-organisms and produce large varieties of metabolites with pharmaceutical potentials. Its modularity structure inspired de-novo designing efforts by recombining desired modules. However, past efforts in this direction are largely unsuccessful. The difficulty in re-engineering new products raise questions on the modulized view: are there unknown functional constraints between different parts of NRPS that favor/disfavor certain combinations of modules or subunits? |
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L70.00340: Probing the Cell-Fate Decision During Infection of E. coli by the Virus Lambda Seth Coleman, Ido Golding, Oleg A Igoshin Lambda is a virus which infects E. coli bacteria, and its infection serves as a paradigm for cell-fate decisions, processes where cells select and transition to stable states. Infected cells can proceed along one of two developmental pathways: lysis, characterized by rampant viral replication and eventual cell death, or lysogeny, characterized by viral dormancy. Despite the decades of research done on this system, fundamental questions remain about what factors drive the decision and the mechanisms by which they act. We are developing models which, calibrated by single-cell resolution experimental data, will be able to shed light on how currently known factors (such as gene copy number, both as an initial condition and as a function of time due to replication, as well as cell volume) influence the decision process, and predict additional factors. We are also investigating explanations for a surprising observation in lambda – the scaling of the probability of a lysogenic outcome with viral concentration exhibits a complicated structure, which can be understood by positing that viruses independently decide their fates. We are developing simple models to test this hypothesis and propose a possible physical mechanism for this intracellular individuality. |
(Author Not Attending)
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L70.00341: A game-theoretic approach to model the transmission of Chikungunya on Reunion Island. David Feagins, Sylvia Klein, Alex Foster, Jonathan Rowell, Igor Erovenko Chikungunya is a viral infection that is spread by mosquitoes of the genus Aedes. Chikungunya victims experience symptoms similar to those caused by the Dengue and Zika viruses but are less likely to die from it. Chikungunya was not a major research interest up until 2004 when a third of the population on Reunion Island, located in Africa, was infected by the disease. This outbreak inspired the creation of mathematical models to study how Chikungunya is transmitted. Driven by these studies, we constructed a game-theoretic model that considers how rational individuals decide to use mosquito repellent to prevent the disease. In our model, individuals make their decision based on a payoff function that takes into account the consequences of being infected and the perceived cost of using mosquito repellent. We found that the usage of mosquito repellent is negatively correlated with the perceived cost of mosquito repellent while keeping the consequences of contracting the disease constant. However, setting the perceived cost of mosquito repellent to zero does not guarantee the eradication of Chikungunya. With this in mind, governments and disease control programs can better understand how to manage the transmission of this mosquito-borne disease. |
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L70.00342: Critical level of epistasis separates trajectories toward evolution of mutational or drift robustness in small populations Chris Adami, Dariya Sydykova, Thomas LaBar, Claus Wilke High mutation rates select for the evolution of mutational robustness, where populations inhabit flat fitness peaks with little epistasis [1]. Recent evidence shows that a different effect shields small populations from fitness declines. In drift robustness [2], populations occupy peaks with steep “flanks”, and positive epistasis. But what happens when mutation rates are high and population sizes are small at the same time? Using a fitness model with both variable epistasis and mutational effect size, we show that the equilibrium fitness has a minimum as a function of the parameter that tunes epistasis, implying that this critical point is an unstable fixed point for evolutionary trajectories. In agent-based simulations of evolution at finite mutation rate, we demonstrate that when mutations can change epistasis, trajectories with a subcritical value of epistasis evolve to decrease epistasis, while those with supercritical initial points evolve towards higher epistasis. These two fixed points can be identified with mutational and drift robustness, respectively. |
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L70.00343: Structured Active Fluids via Interfacial Nanoparticle Assembly Paul Kim, Joe Forth, Zvonimir Dogic, Pooja Chandrakar, Thomas Russell The transport of ordinary liquids tends to be driven by pressure difference, whereas for active fluids (or biological matters), the transport is autonomous and/or isotropic, governed by the gradient in specific chemical. Wu et al. recently discovered the emergence of spontaneous directional flow of active fluids, consisting of microtubule filaments and kinesin molecular motors, upon their confinement in a variety of microfluidic channels [Science 24 Mar 2017: Vol. 355, Issue 6331]; when confined in loops of toroidal and cylindrical channels, the flow persisted in one direction, either clockwise or counterclockwise. Here, we observed the same active fluid confined in channels of similar geometries, which are made of a thin layer of nanoparticles. By extruding or molding a dispersion of charged nanoparticles in an immiscible solution of oppositely charged surfactants, liquids can be mechanically stabilized (or structured) in an arbitrary shape by jamming of nanoparticle surfactants at the liquid interface. The flow of active fluid and its consequence to overall structures are observed in situ by fluorescent microscopy. The interactions between the liquid interface and active fluid is also studied. |
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L70.00344: Emergence of E. coli Critically Buckled Motile Helices Under Antibiotic Stress Trung Phan, Ryan Morris, Robert Austin, Matthew Black, Julia Bos Bacteria under external stress can reveal unexpected emergent phenotypes. We show that the intensely studied bacterium E. coli can transform into long, highly motile |
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L70.00345: Simple Stochastic Simulations for Visualizing and Testing Models of Gene Expression and Proofreading Kevin Y Chen, Daniel Zuckerman, Phil Nelson To better visualize the stochastic nature of cellular processes and how they unfold over time, we developed a simple Gillespie algorithm to simulate two important non-equilibrium statistical processes, gene expression and translation error correction. |
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L70.00346: Modeling the collective behaviour of Dictyostelium discoideum under directed migration Viktor Teshome Belay, Wolfgang Losert Cellular migration is a function that is ubiquitous across a vast number of organisms. This phenomenon is observed in many biological functions such as embryogenesis, tissue regeneration, tumor metastasis, muscle contraction, and more. Cellular migration is influenced by various factors; principally, by chemical, mechanical, and electrical cues. We utilize the model organism Dictyostelium discoideum to study the effects of nanotopographical guidance and electrostatic fields on the motion of cells. We develop a cell-scale stochastic model of the influence of nanotopography, electrostatic fields, and chemical signaling by the secondary messenger cyclic adenosine monophosphate on the motion of D. discoideum cells. Model simulations show that unidirectional guidance by nano-ridges allows for D. dictyostelium streaming and aggregation, while bidirectional nanotopography creates a cell bifurcation in which there is little to no streaming or aggregation. In addition, simulations indicate that D. discoideum cells exhibit directed collective motion when under the influence of a unidirectional electric field. |
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L70.00347: Designing Compact Microfluidic Structures to study Cancer Cell Metastasis via Flow-less Spatial and Temporal Gradients Arturo Ruben Diaz, Ileene Ashley Diaz, Dwayne G. Stupack, Dragos Amarie Metastasis, the migration of cancer cells away from an original tumor to other tissues, is the primary cause of morbidity and mortality in cancer patients. This migration is controlled by complex biomechanical processes and triggered by diverse stimuli. We seek to develop a set of microfluidic tools to investigate metastasis that will allow us to analytically pinpoint triggering factors by studying changes in cell migration as prompted by as few simultaneous stimuli as possible. These devices are microfluidic structures that produce stable, controlled gradient flows across and along a microfluidic gradient chamber. They will allow us to study how extracellular chemical gradients of various compositions and/or concentrations drive ovarian carcinoma cell migration. These tools follow our previous work and use the concept of splitting and recombining flows through a series of bifurcations and trifurcations, while introducing a gradient chamber separate from the cell culture chamber. Bright field and epi-fluorescence microscopy will be used to characterize these devices. |
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L70.00348: Bacterial Physiology during Intercellular Signaling Shiqi LIU Cell-cell communication plays an important role in many biological processes. The communication is often mediated by diffusing chemical signals released by cells. Here we study how the bacterial physiological state responds to the intercellular signals and how individual cells benefit from those signaling-related processes. A better understanding of bacterial physiology during intercellular signaling could enable us to manipulate the behavior of cells and may help to understand biofilm formation. |
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L70.00349: Propagation of Wall-Less Bacteria Yisen LI Normally bacterial growth relies on the peptidoglycan cell wall. However, cells in a wall-free state can propagate in a wall-independent manner, which remains poorly understood. We will present our recent work on continuous propagation of wall-less bacteria and colony formation. The underlying mechanism is relevant to antibiotic resistance of pathogens. |
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L70.00350: Anomalous flip-flop of DMPC in lipid membranes Neti Bhatt, Ursula Perez-Salas, Lionel Porcar, Yangmingyue Liu, Michael Stanfield Although the study of the passive movement of lipids between and within membranes can give insight into lipid transport regulation by providing a way to gauge the energetic cost on active metabolic pathways, published work on the spontaneous transfer of lipids report a wide variation in the rates of transfer between and particularly within membranes. Non-invasive approaches like time resolved small angle neutron scattering or sum -frequency vibrational spectroscopy have shown that the movement of lipids is extremely sensitive to chemical structures of molecules finding that the transfer rates of unaltered lipid molecules are dramatically different from their chemically tagged counterparts. My group performed Neutron Scattering experiment and found that DMPC flip-flop rates display two Arrhenius states well above DMPC’s melting temperature. I will report on measurements of the flip-flop rates in DMPC using nuclear magnetic resonance spectroscopy and membrane order and fluidity using Laurdan generalized polarization, DPH anisotropy respectively, to reveal the nature of this intriguing behavior. |
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L70.00351: Deterministic and stochastic analysis of an oncolytic infection model Karan Buntval, Hana M Dobrovolny Mathematical models of biological processes have had a history of high predictive power of both experimental data and preliminary drug tests. Models that aim to predict the dynamics of oncolytic virus infections have previously focused solely on 3 populations, i.e., the cancer cells, virus-inflicted cancer cells, and the virus itself. Considering that most tumor populations have a substantial proportion of healthy cells, an oncolytic model that rightly adjusts for this increased fraction would provide insight into dual cell dynamics. Our findings elucidated that certain parameter variations with the tumor proliferation, infection, virus replication, and infected cell dissolution rates eventually allowed for the negation of cancer cells while simultaneously keeping the healthy cells alive. A stochastic interpretation of the model was further utilized to more authentically characterize the probabilistic events during an infection. In addition to preventing the oscillatory behavior observed with the deterministic model, it also confirmed the initial denouement of an extinct cancer population and thriving non-cancerous cells. |
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L70.00352: Assessing tumor treatment modalities using an allometric model Jennifer Firehammer, Allen Garner Allometric growth models apply universal growth laws to predict growth of organisms and structures from very small to very large and have accurately modeled avascular tumor growth. These models have been extended by coupling the allometric growth law to a reaction-diffusion equation for nutrient transport to model necrotic core formation [A. L. Garner, Y. Y. Lau, T. L. Jackson, M. D. Uhler, D. W. Jordan, and R. M. Gilgenbach, J. Appl. Phys. 98, 124701 (2005).] and incorporated vascularization by applying energy arguments to incorporate vascularization [A. B. Herman, V. M. Savage, G. B. West, PLoS ONE 6, e22973 (2011).]. Recent developments of artificial, 3D tumor in vitro models that can incorporate vasculature provide a future means to assess chemical, physical, and combined treatments [R. Michna, M. Gadde, A. Ozkan, M. DeWitt, and M. Rylander, Biotech. Bioeng., https://doi.org/10.1002/bit.26778] for eventual clinical use. In this study, we modify the allometric growth model to assess the implications of dosage profiles on tumor growth. For a constant dosage, we observe that a subthreshold treatment reduces the steady-state tumor size while a suprathreshold amount destroys the tumor. The therapeutic implications of these results and future experiments will be discussed. |
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L70.00353: Tracking the Kinematics of Zebrafish Startle Responses Following Ablation of Sensory Hair Cells Peter Jaeho Cho, Mohamed Ahmed Ramy, Yagmur I. Ozdemir, Rana Barghout, Josef Trapani, Ashley Carter The survival of a zebrafish depends on its ability to detect and respond to external stimuli. Indeed, to avoid predators, zebrafish startle when subjected to sudden mechanical stimuli. Here our goal is to characterize the kinematic properties of the zebrafish startle response following ablation of sensory hair cells to determine the role of these cells as well as observe whether differences in the neural circuitry lead to measurable physical changes in the kinematic properties. To measure these kinematic properties, we head mounted a single larval zebrafish, induced a startle, and took videos of tail movement with a high-speed camera. Videos were analyzed in MATLAB to find the tail midline, allowing us to measure the kinematic differences in tail angle, velocity, acceleration, and curvature. Further work could observe twist and out of plane motion of the tail. Differences in these kinematic parameters would highlight how zebrafish behavior is affected by an altered neural circuit. |
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L70.00354: Scale-dependent relationships in human language Aakash Sarkar, Marc Howard Many models of human language extract statistical regularities of natural language to estimate “meaning”. Mutual information between words in natural language has been shown to decay as a power law (Lin and Tegmark, 2017). Despite this evidence for scale-invariant statistics, statistical models of language typically impose a strong scale. We study the scale-dependence of language using Word2Vec (Mikolov et al., 2013), a shallow neural network model which generates a vector embedding of words by training over a corpus of text. We modify the Word2Vec algorithm to choose neighbors of a target word with an exponentially decaying distribution, and look at the embedding generated for a broad spectrum of scale parameters. It seems to appear that different syntactic and semantic relations (as classified in several tests developed by Mikolov et al.) seem to be best expressed at different word scales. Word similarities between neighbors seem to capture qualitatively different behavior across a range of word-scales, often peaking at distances that would not be captured by an embedding sampled at a single, particular scale. These results point toward the importance of developing scale-free models of semantic meaning. |
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L70.00355: Temporal contingency and informativeness in Laplace domain Konstantin Tiurev, Marc Howard Associative learning in conditioning protocols is traditionally thought to depend on temporal contiguity between the stimuli. However, recent proposals suggest that temporal contingency rather than temporal contiguity is responsible for associative learning. That is, associations to the unconditional stimulus develop whenever it provides meaningful information about the expected time of reinforcement. Such information-theoretic framework has recently been considered in the context of Pavlovian conditioning, operant conditioning, and behavioral neuroscience. Here we develop information-theoretic approach to the long-range temporal credit assignment subject to several cognitively-inspired constraints. First, we assume that the system cannot possibly measure the joint statistics of the past combinations of stimuli. Second, our method assumes that the approximate stimuli history is available in the form of the inverse Laplace transform, which makes the method time-local and scale-invariant and helps to overcome major drawbacks of traditional approaches to the long-range credit assignment problem. The result is a biologically-plausible, computationally efficient model of associative learning, one of the fundamental processes in neural function. |
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L70.00356: An Electro-Mechanical Model of the Axon John Leventis, Gary Pennington Recent research into the electro-chemical effects of neural damage have provided evidence for interactions between deformations of the axonal membrane and the flow of charges thru its ion channels. Furthermore, traveling mechanical membrane waves in the axon have been shown to accompany the action potential. It seems possible that a more complete understanding of the true phenomena governing the transmission of an electric signal along a myelinated axon must incorporate more than just the electro-chemical mechanisms. We report simulation of signal transport in neural axons incorporating both electro-chemical and mechanical strain-related membrane deformations. Myelinated axons under normal and abnormal stressed conditions are compared. The results are used to investigate interdependencies between strain-related membrane deformations and electrical signals along the membrane. We model electro-mechanical behavior due to cell damage, disease, and abnormal ionic concentrations around the cell. We hope that making explicit the interdependencies between mechanical waves and electrical signals within the axon will prove useful to further biophysical research. |
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L70.00357: Development of a Behavioral Assay using Fluidic Devices to Study Learning and Memory in Cuttlefish Larvae Colton Sellars, Jessica Bowers, Vinoth Sittaramane, Dragos Amarie We developed behavioral assays to investigate the behaviors of cuttlefish hatchlings. Despite their behavioral complexity, little is known about cuttlefish behavior due to chemical stimuli. Current work done in 6-well plates shows the need for designing new fluidic device to manipulate chemical flow, delivery times, and allow event recording. Since behavioral assays for aquatic species require a flow-through design, our chip consists of joined channels, while diffusion coefficient calculation allowed us to evaluate flow rates. Our fluidic device provides more control thus creating a complex environment for cuttlefish hatchlings to explore. Using this device and tracking software, we can quantify the movement of cuttlefish in response to different stimuli. In these trials we aim to determine how prey cues have an effect on the cuttlefish navigation throughout the new environment. By providing food rewards for performing tasks, we can determine cuttlefish ability to learn to discriminate specific chemical information. This work presents a novel method for studying animal behavior in a dynamically changing chemical environment. |
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L70.00358: Investigating material properties of fish schools with dynamic light fields Pranav Kayastha, Aawaz Pokhrel, James Puckett Many social animals, such as birds, fish and insects, exhibit complex group behavior. Models have shown that simple local interactions between individuals gives rise to the emergent self-organized macroscopic states such as flocks, swarms, or schools. We investigate the material properties of laboratory fish schools by exploiting the negative phototaxicity of Rummy-Nose Tetra (Hemigrammus blehri) to strain the school using projected dynamic light field. To do this, we use an overhead high speed camera to record individual fish trajectories in a quasi-two-dimensional tank. The strain is generated by projecting two dark regions moving in opposite directions, where fish use both social and environmental information to determine their behavior. We find that schools can undergo large deformations before collapsing back to one of the regions. We show that the school exhibits a linear stress-strain relationship, analogous to the Hooke’s law. |
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L70.00359: CHEMICAL PHYSICS
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L70.00360: Quantum Chemical Investigations on Heavy Ligand Atom Induced Large Magnetic Anisotropy in Mn(II) Complexes. Sabyasachi Roy Chowdhury, Sabyashachi Mishra In Single Molecule Magnets (SMM) metal ions are considered pivotal towards achieving |
(Author Not Attending)
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L70.00361: Modeling X-ray Absorption Spectroscopy with Relativistic TDDFT Xiaosong Li X-ray absorption spectroscopy (XAS) is an element specific probe that has been used to understand the local electronic and binding environment around metal centers. Electronic structure theory has become an important aid in interpreting XAS spectra. While K-edge spectra have been investigated in great detail, the modeling of L-edge spectra poses several unique challenges. First, the L-edge spectrum is composed of multiple features: L1 corresponding to the 2s orbital, and L2,3 corresponding to 2p orbitals, which are split into 2p1/2 and 2p3/2 levels by spin-orbit coupling. Additionally, with density functional theory (DFT) it also becomes necessary to make modifications to handle non-collinear spin densities in the presence of spin-orbit coupling. We model the L2,3 spectra for several molecules with variety of model chemistries using exact two component TDDFT (X2C-TDDFT). With the X2C-TDDFT method we are able to include the one-electron spin-orbit coupling terms variationally from first principles. An analysis of the molecular orbitals involved in the transitions yields valuable theoretical information that can be used to connect the local electronic structure with experimental observables. |
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L70.00362: Excited State Time-Resolved Vibrational Dynamics: the Challenge of Charge Transfer Complexes Federico Coppola, Paola Cimino, Umberto Raucci, Maria Gabriella Chiariello, Nadia Rega
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L70.00363: Speeding-up Ab Initio Simulations: Novel Approaches for Extended Lagrangian Molecular Dynamics Fulvio Perrella, Alessio Petrone, Nadia Rega Modern theoretical chemistry is prompted to give insight into ultrafast phenomena from an atomistic point-of-view and to give an interpretation of the experimental data from time-resolved spectroscopies. Ab initio molecular dynamics (AIMD) is the prominent approach to capture both electronic and nuclear relaxation events.1 Among different approaches to molecular simulations, the Extended Lagrangian AIMD techniques appear to give best performances with respect to the accuracy/cost ratio. The fictitious electronic mass is a crucial parameter, because it has to ensure an efficient propagation of the electronic degrees of freedom, while keeping a strong degree of adiabaticity.2 Current implementations are based on a uniform or an energy-based weighting of atom centered basis functions and often cannot capture their core or valence-like character. A novel mass weighting scheme, based upon a rational classification of the atomic functions, will be proven to be consistently more reliable, while avoiding errors typically occurring with fixed energy thresholds. Such an approach may allow larger time-steps, while ensuring a strong physical soundness to the simulation. |
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L70.00364: Using geometric phases to separate overall rotation and internal motions in classical and quantum molecular dynamics F. J. Lin In 1959, Aharonov and Bohm pointed out that electrons could be affected by vector potentials without an external magnetic field. To make the wave functions in vector potentials single-valued, an ad hoc phase shift is required. This phase shift exemplifies a geometric phase (or Berry’s phase). Similarly, Mead and Truhlar described an ad hoc phase shift required for nuclear wave functions describing three-body molecular dynamics in the Born-Oppenheimer approximation. In their “molecular Aharonov-Bohm effect,” Mead and Truhlar assumed decoupled overall rotation and internal motion and considered the effects of a conical intersection. Instead of neglecting coupled overall rotation and internal motion, now this coupling is used to create a frame with decoupled overall rotation and vanishing classical and quantum geometric phases. An extension of the classical dynamics describes the quantum dynamics of a three-body molecular system in the Born-Oppenheimer approximation. This theoretical approach agrees with observations of spectra of rare gas-diatomic molecule complexes and observations of triatomic photodissociation dynamics. |
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L70.00365: Calculations of small molecules using the Highly Accurate N-DEterminant (HANDE) quantum Monte Carlo software package Hayley Petras, Tina Mihm, James Shepherd We use calculations of small molecules and the uniform electron gas to illustrate the capability of HANDE, a open-source software package that calculates stochastic estimates for high accuracy quantum chemistry methods. We choose to focus on full configuration interaction and its finite temperature variant, density matrix quantum Monte Carlo. We describe how strong correlation and other phenomena manifest in the context of this and the initiator approximation to these methods. |
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L70.00366: Theoretical Insights into the Mechanisms of Aggregation-Induced Emission of a Tetraphenylethylene Norifumi Yamamoto The aggregation induced emission (AIE) of tetraphenylethylene (TPE) was studied theoretically. The TPE has been known to exhibit the AIE, which is non-emissive in dilute solutions but becomes highly emissive in solid or aggregated state. In this study, the AIE mechanism of TPE was investigated by using electronic structure calculations, together with molecular dynamics (MD) simulations. The results of electronic structure calculations showed that potential energies of TPE for electronic ground (S0) and first excited (S1) states are degenerated at a conformation with the twist angle of 90° around its ethylenic C=C bond, which can lead the fluorescence quenching of this molecule in dilute solutions. The results of MD simulations revealed that the TPE in aggregated state tends to assemble in close contact, where the ethylenic C=C bond rotation is markedly restricted, preventing the fluorescence quenching via the S0/S1 conical intersection; the TPE in THF solution, however, proceeds the barrierless non-radiative transition. These results gave a clear picture of the AIE mechanism of TPE. |
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L70.00367: Single-electron excitations from thermally-assisted-occupation reference Shu-Hao Yeh, Aaditya Manjanath, Jeng-Da Chai, Chao-Ping Hsu The linear response time-dependent density functional theory (LR-TDDFT) has been broadly used to investigate excited-state properties of various molecular systems. However, current LR-TDDFT methods heavily rely upon outcomes from ground-state DFT calculations. For systems with small HOMO-LUMO gaps, single-determinant ground-state DFT may be prone to non-dynamical correlation, and hence, LR-TDDFT results can be inaccurate. Traditionally, nearly degenerate orbitals require proper treatment of non-dynamical correlation, which usually involves active-space treatments. Recently, the thermally-assisted-occupation (TAO) DFT scheme was proposed, which explicitly incorporates the non-dynamical correlation effect in the ground-state simulation, but retains the low computational complexity of conventional DFT. The aim of this work is to combine ground-state TAO-DFT with LR-TDDFT framework to study excited-state phenomena. The preliminary simulations successfully capture the dissociation feature of the first triplet excited state of hydrogen molecule, which is not the case for conventional TDDFT. |
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L70.00368: Bicarbonate charging of hydrophobic/water interfaces Francois Ganachaud, Julien Bernard, Xibo YAN, Antonio Stocco Most surfaces in contact with water are negatively charged. The reason for that has long been debated in the physics community as arising either from hdyroxide ion adsorption or water reorganization towards a hydrophobic interface. We have recently proposed another explanation coming from the carbonation of water. Bicarbonates, which in distilled water are the most present ions at intermediate pHs (from 5 to 10), are chatropic ions that stick to interfaces. We made use of a combination of interfacial tension measurements of oil droplets in water, and nanoprecipitation assays of polymers in a large range of pH, to show such affinity of HCO3- for hexadecane oil and PMMA. This prefered adsorption of bicarbonate allows also explaining why freeze/thaw cycles contribute to emulsifying oil/water mixtures. |
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L70.00369: Computational Study of the Intermolecular Interactions Hg and Hg (II) With Thiols in Aqueous Environments. JICLI ROJAS, Juan Camilo Galvis, Alfredo Lora, Carlos Pinilla, Neil Allan Hg water contamination is one of the most common problems of gold mining. It is known that Hg has a great capacity to form compounds, especially when it reacts chemically with aquifer sources transforming it into methyl-mercury [CH3Hg] +; a powerful neurotoxic that tends to accumulate, through the trophic chain, in fish, humans and wildlife that feed on them, causing irreversible effects on health. Currently there are no efficient methods for the treatment of water contaminated by Hg. In this work we systematically study the interaction energies between Hg, Hg (II) and methylmercury species with the -SH (thiol) group of the compounds Cysteine C3H7NO2S (1), 3-mercapto-3-methylbutan-1-ol C5H12OS (2), Silanol C3H10O3SSi (3) and Dimercaprol C3H8OS2 (4) in aqueous medium, using DFT in order to identify the compound with the most favorable interactions, which can be used for functionalization and so to produce new materials for the extraction of Hg. The results show that interactions with elemental mercury (Hg) are thermodynamically favored. However, with mercury in its ionic form (Hg II), the interactions that are favored are those when compound (2) and compound (4) were used. Our study hints on the possiblity to use thiols extracted from local vegetables and fruit sources. |
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L70.00370: A Theoretical Study of Novel Composite Clusters of Platinum Metals Ajit Hira, Jose Pacheco, Ruben Rivera, Matilda Fernandez, Alexandra Valdez Material shell composites.of platinum (Pt) and palladium metals have great stability and remarkable physical and chemical properties. In light of our previous work on the small atomic clusters on metallic clusters, we present here an Ab-initio quantum-mechanical study of the Ptn, Irn, and Osn ( n= 1-9 ) clusters, their hybrids MiNj ( M= Pt, Ir, Os; N= Pt, Ir, Os; i= 1-6; j= 1-6), and their composites of these metal clusters with palladium (Pd) clusters. Our theoretical approach is to utilize the ab initio methods of quantum chemistry to derive optimal geometries for the clusters of interest. Of particular interest in this research are the Pt6 and Pt8 rectangular parallelepipeds, and the Pt8, Pt9, Pt8Pd8, Pt8Pd9 cubic clusters. We examine the implications of this research for the self-assembly of metallo-supramolecular structures, by the directional bonding approach. Also, of interest here is the recent experimental work that showed that Pt clusters deposited on Pd shell over Au core nanoparticles (Au@Pd@Pt NPs) exhibit unusually high electrocatalytic activity for the electro-oxidation. |
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L70.00371: Structure and optical properties of In1-xRExTaO4 (RE= Er, Yb) and their oxynitrides, an evaluation as photocatalysts for water splitting Juan Cruz Puerto, Cristina Ramírez, Pablo De la Mora, Gustavo Tavizón Ta2O5 based photocatalysts show a band gap of about 4.0 eV, this implies that they should be used under UV electromagnetic radiation, this condition limits its applications. Zou, Z. et al. [1] prepared visible-light active photocatalyst with formula InTaO4:NiO, with a wolframite structure and a band gap of 2.6 eV; more recently this system was reviewed by Malingowsky, A. et al. [2] and they found a direct band gap of 3.96 eV for the nickel doped InTaO4 compound. In this work, we studied the In1-xRExTaO4 (RE= Er, Yb, 0.0≤x≤2.0) solid solution with a wolframite structure and we found that for the Yb case the system it does not exhibit absorption in the visible region of the electromagnetic spectrum, while the Er system it shows a rich absorbance spectrum in the visible region. Probably this absorbance signals are associated to internal f-f electronic transitions and could be active in photocatalysis under visible radiation. |
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L70.00372: Theoretical modeling of coherent proton transfer dynamics and pump probe spectroscopy simulation Luhao Zhang, Greg Scholes Proton transfer reaction is ubiquitous in chemistry and biology. Pump probe spectroscopy shows general feature of fast rising and oscillation signal of excited state proton transfer which can only be explained by quantum mechanics. However, due to the interplay of electron rearrangement, nuclear vibrations, skeletal torsion and molecule-solution interaction, it's difficult to use ab-initial quantum dynamics calculation to illustrate pump probe signal. Here, we adopt the a vibronic coupling Hamiltonian and used methods of open quantum dynamics to simulate pump probe signal of HBT(2-(2′-Hydroxyphenyl)benzothiazole) and compare with experiment. Our method will make a brige between experiment and ab-intial calculation, and also provide a framework to describe a chemical reaction in a wave function(density matrix) perspective. Furthermore, because of the quantum mechanical nature of excited state proton transfer, it's possible to realize a superposition of two pathways for a dimer molecule with two proton transfer sites, which brings a new mechanism for general chemical reaction. Using similar model Hamiltonian, we found for isolated dynamics, a superposition reaction shows interference pattern of nulcear density while single proton transfer does not. |
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L70.00373: Dynamic scaling in stochastic chemical kinetics Jonah Greenberg, Jason R. Green Universality classes are often comprised of seemingly dissimilar physical systems. Here, we draw a formal analogy between surface-roughening processes and the stochastic kinetics of fundamental chemical reactions. We simulate the chemical kinetics of several classes of reactions with Gillespie’s exact stochastic simulation algorithm and analyze the dynamic scaling of a quantity analogous to the surface roughness, w. For kinetics at chemical equilibrium considered thus far, the growth exponent is β=1/2. The dynamic exponent z, however, depends on the molecularity of the reaction. For simple cases these computational results can be verified analytically through the associated master equations. We observe a richer collection of exponents and scaling relations for nonequilibrium kinetics. Overall, these results suggest, just as in surface-roughening phenomena, that seemingly dissimilar chemical systems may also be partitioned into universality classes, some known and others new. |
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L70.00374: Effect of surface morphology on kinetic compensation effect: interactions vs. energetic heterogeneity Nayeli Zuniga-Hansen, Leonardo Silbert, M. Mercedes Calbi The kinetic compensation effect, observed in many fields of science, is the systematic variation in the apparent magnitudes of the Arrhenius parameters, the activation energy Ea and the preexponential factor ν, as a response to perturbations. In principle, a change in Ea results in a change in the configurational entropy of the system, which appears as variations in ν throughout an activated process. As part of a systematic study, we compare the effects of interactions on these parameters during the thermal desorption of quasi spherical molecules from a 2D glassy surface to the effects of surface energetic heterogeneity. The results of this study show that the decrease in configurational entropy is more pronounced in the presence of interactions. We also explore the role that diffusion plays in the extent to which the parameters offset each other. These results provide a deeper insight into the microscopic events from which compensation effects and isokinetic relations originate in this system, suggesting similar mechanisms may be at play in other systems where compensation |
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L70.00375: Molecular Dynamics Simulations of the Elastic and Structural Properties of Calcium Aluminate Glass: Effects of Low Silica Contents Hicham Jabraoui, Michael Badawi, Abdellatif Hasnaoui, said ouaskit, Yann Vaills We have used classical molecular dynamics to investigate the elastic constant behaviors of low silica calcium aluminosilicate glasses where SiO2=5–25 mol% and [CaO]/[SiO2] =2. To compute the elastic constants, we have used two methods; the minimization energy at zero temperature (Zero-T) and a second one that allows calculating the elastic constants at finite temperature (FT)[1]. To evaluate the reliability of these methods, the obtained results are compared with those already measured by Brillouin light scattering spectroscopy (BLS). To this end, we show that elastic constants decrease with increasing silica content, which can be correlated with some structural features such as oxygen types and short-range order parameters. However, these properties are not easily accessible from experiment [2]. Therefore, our simulations complement well the current knowledge on the influence of low silica contents on the physicochemical properties of calcium aluminate glasses. |
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L70.00376: Like dissolves like: how like need they be? A statistical field theory for polar liquids and their mixtures Bilin Zhuang, Zhen-Gang Wang We have been taught the empirical “like-dissolves-like” rule in secondary school chemistry classes, but how like must the solvents be? This question does not yet have a good quantitative answer because of the difficulty in finding a general description for mixture interactions. Here, we present a theory for polar liquids and their mixtures, developed using a statistical field approach. This approach allows us to avoid the use of ad hoc mixing rules, and thus provides a more holistic description of liquid mixtures. The resulting theory consists of simple algebraic expressions for the free energy and the dielectric constant of the liquid, based on just the dipole moments and the sizes of the constituent liquid molecules. Without the use of any adjustable parameters, the theory very well predicts the miscibility for a variety of liquids, thus provides a quantification for the well-known empirical “like-dissolves-like” rule. |
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L70.00377: WITHDRAWN ABSTRACT
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L70.00378: Modeling of One-Dimensional Diatomic Molecules through Density Functional Theory Kyle Jones, Antonio C Cancio We have developed a code to solve the Schrodinger equation of one-dimensional systems of electrons numerically in a plane wave basis. We have tested the accuracy of the code by performing convergence tests versus cell size and plane wave number, for the square-well and the Poschl-Teller well. We use this to calculate numerically accurate electron and kinetic energy densities and compare to simple density functional models for these quantities. We plan to use this code to investigate the results when two potential wells are pulled apart. Density functional theory (the use of only the density to calculate energies) is known to fail in three dimensions as electric bonds are broken and we expect this to be a problem in one dimension as well. Our one-dimensional code will allow for quick testing of new models and theories to see if they are viable avenues for better describing electronic bonding. |
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L70.00379: WITHDRAWN ABSTRACT
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L70.00380: Self-interaction effects in molecular dissociation curves Koblar Jackson, Alexander Johnson, Juan Peralta, Kamal Sharkas The Fermi-Löwdin Orbital Self Interaction Correction (FLO-SIC) removes unphysical electron self-interaction from Density Functional Theory (DFT), the most widely used first-principles method in condensed matter and chemical physics. Self-interaction errors can be particularly pronounced in situations where bonds are stretched, such as when an atom is dissociated from a molecule. To study the effectiveness of FLO-SIC in this context, we calculated dissociation curves corresponding to removing one H atom from each of the molecules LiH, BeH2, BH3, …, HF, and one F atom from each of LiF, F2,and FCl. To get a statistical measure of performance, we compare FLO-SIC-DFT and DFT dissociation energies to accurate reference energies at four points along each curve. We find that FLO-SIC improves the performance of the local density approximation (LDA) at all separations, while for the generalized gradient approximation in the Perdew-Burke-Ernzerhof (PBE) form the performance is improved only for large separations. FLO-SIC corrects the tendency of both LDA and PBE to predict charged fragments in the large separation limit. |
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L70.00381: MD Simulation of Ligand Migration and Substrate Binding in Lipoxygenases VIPIN KUMAR MISHRA, Sabyashachi Mishra
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L70.00382: Nano-Species Release System Activated by Enzyme-Based XOR Logic Gate Yaroslav Filipov, Maria Gamella, Evgeny Katz An enzyme-based XOR logic gate was realized at interface of an alginate-modified electrode. The biocatalytic production of H2O2 inside the alginate film was controlled by logically processed input signals. The in situ generated H2O2 was decomposed to yield free radicals in a Fenton-type reaction catalyzed by iron cations, which were present in the alginate film as cross-linkers stabilizing the hydrogel. The produced free radicals (*OH, *OOH) resulted in decomposition/dissolution of the alginate film removing it from the electrode surface and stimulating release process of magnetic nanoparticles (MNPs) functionalized with a fluorescent dye and entrapped in the alginate film. The release of the MNPs was analyzed by following fluorescence appearing in the solution. The release process followed the logic features of the XOR gate. The present system is the first realization of the enzyme-based XOR gate functionally integrated with the downstream actuation process in the form of the signal-stimulated release. |
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L70.00383: Molecular Modeling of 1-Benzazepine Analogues that bind to the ACh Protein (2PH9) Using Hyperchem and AutoDock Paola Colon, Astrid Santiago Ligand interactions of the designed analogs to neuronal nicotinic Acetylcholinesterase receptor (nAChR) are being studied to see which one fit into the binding site of an ACh binding protein PDB code (2PH9).1-Benzazepine analogs improve allosteric positive modulation of the nicotinic α-7 acetylcholine receptors.The Heat of Formation, obtained using Schrödinger equations, of 8 benzazepines analogues that were designed in the Hyperchem program were calculated on the PM3 Hyperchem quantum levels.They were pre-optimized using MM + and the PM3 semi-empirical method with the Polak-Ribière conjugate gradient.The protein-ligand binding of these benzazepine analogs to ACh binding protein PDB code is being determined using the Auto Dock Tools and AutoDock Vina programs.The Affinity of the analogues under studies could be calculated using the Command Prompt of the computer, assigning specific x, y and z coordinates with a specific grid box size. It’s obtained that the ligand with the best interaction with the protein was 7-8 dimethoxy-1 BNZ-cinnamic acid with an affinity of -8.6kcal / mol and a Heat of Formation equal to -126.06 kcal / mol. These results, of the 8 ligands, were compared to Galantamine which is the commercial drug used to treat neurodegenerative diseases. |
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L70.00384: Modeling Circular Current Resonances in a 6-Quantum Dot Ring Yong Joe, Eric Hedin A nanoscale ring configuration, modeled as a 6-quantum dot ring, is investigated computationally to study the behavior of circular current resonances. The computational method utilizes the tight-binding approximation to the Schrodinger Equation to solve for the transmission and circular transmission as a function of electron energy, external magnetic flux, and other system parameters. Large amplitude resonances of the circular transmission are found to occur when two poles of the transmission are separated along the imaginary axis. These resonances demonstrate a high degree of flux-sensitivity at specific energy values and flux ranges. Flux-dependent interference between the transmission poles and zeros in the complex energy plane affects the magnitude of the circular transmission resonance amplitudes. The circular transmission and its corresponding current-vs.-voltage characteristics may serve as a nano-sensor, providing a higher degree of correlation with the external flux than is observable with the normal transmission alone. |
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L70.00385: Method for the Growth and Stabilization of Rare Earth Nano-Particles Patrick Talbot, Pei-Chun Ho We are developing a process to create rare-earth metal (REM), nanoparticles (NPs), to the end of studying their magnetic and electrical properties. The large redox potential of REMs hinders the formation and stabilization of these NPs, requiring: a strong reducing agent to form the NPs, and their protection from ambient conditions. |
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L70.00386: Biosensors Protected by Biomimetic Membrane with Carbon Nanotube Porins Xi Chen, Huanan Zhang, Ramya H Tunuguntla, Aleksandr Noy Limited biocompatibility and fouling propensity can restrict real-world applications of a large variety of biosensors. Biological systems are adept at protecting and separating vital components of biological machinery with semipermeable membranes that often contain defined pores and gates to restrict transmembrane transport only to specific species. Here we use a fouling-resistant membrane, which mimic the architecture of cellular membranes in nature to protect biosensors. We integrate silicon nanoribbon transistor sensors with an antifouling lipid bilayer coating that contains carbon nanotube porin (CNTP) channels and demonstrate robust detection of proton and cations in a variety of complex biological fluids. Preliminary results of CNTP as a conduit bridging through cell membranes are also discussed. |
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L70.00387: WITHDRAWN ABSTRACT
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L70.00388: Iron Oxide Nanoparticles with Controlled Size and Shape Shirin Pourmiri, Vasileios Tzitzios, George C Hadjipanayis Controlling the shape of Fe3O4 particles is still a big challenge. It has been shown that the SAR value for hyperthermia measurements, has been related to the magnetic anisotropy of the nanoparticles which depends on their size and shape [1]. Therefore, it’s very important to control the shape and the size of Fe3O4 nanoparticles precisely. |
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L70.00389: Resonance Energy Transfer in Arbitrary Media: Two Entangled Photons Kobra Nasiri Avanaki We report the resonance energy transfer between two uncoupled two-level atoms jointly excited by temporally entangled field. |
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L70.00390: Electrochemical Hydrogen Evolution Reaction of Supported Pt Nanoclusters on MoS2: Cluster Expansion Investigation Timothy Yang, Teck Tan, Wissam Saidi Supported metal nanoclusters on MoS2 have shown catalytic activity towards hydrogen evolution reaction (HER) that is comparable or better than bulk Pt. We use density functional theory calculations in conjunction with cluster expansion and ab initio thermodynamics to investigate the activity of supported Ptnanoclusters on MoS2. We determine the hydrogen adsorption configurations under HER conditions by including multiple adsorption sites. Our results show that both Volmer-Heyrovsky and Volmer-Tafel reactions are facile on the cluster while as only the Volmer-Tafel reaction is observed for Pt (111) surfaces. This results in enhanced catalytic activity of the nano cluster. The underpinning of this behavior is discussed. |
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L70.00391: Ab-initio investigation of water adsorption and hydrogen evolution on Co9S8 and Co3S4 low index surfaces Marco Fronzi, Hussein Assadi, Michael J. Ford We used density functional theory approach, with the inclusion of a semi-empirical dispersion potential to take into account van der Waals interactions, to investigate the water adsorption and dissociation on cobalt sulphides Co9S8 and Co3S4 (100) surfaces. We first determined the nanocrystal shape and selected representative surfaces to analyse. We then calculated water adsorption and dissociation energies, as well as hydrogen and oxygen adsorption energies, and we found that sulphur vacancies on Co9S8 (100) surface enhance the catalytic activity toward water dissociation by raising the energy level of un-hybridized Co3d states closer to the Fermi level. Sulphur vacancies, however, do not have a significant impact on the energetics of Co3S4 (100) surface. |
(Author Not Attending)
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L70.00392: Modifying H2 adsorption and desorption on palladium using polymers – a first-principles study Lucy Cusinato, Anders Hellman In a future hydrogen-based energy system it will be crucial to have sensors that are able to detect hydrogen leaks immediately. DOE has proposed very demanding performance targets, and in an effort to meet these, optical nanoplasmonic hydrogen sensors based on hydride-forming palladium nanoparticles have been introduced. Experimentally, the presence of metal-organic frameworks or polymers has been shown to lower the apparent activation energy of hydrogen adsorption/desorption. Here, we study this phenomenon from a theoretical (using DFT) point of view. The behavior of palladium and palladium hydride nanoparticles towards H2 adsorption and desorption, with and without polymer (PTFE, PVDF and PMMA) coating, is studied. A particular focus is set on how to model this kind of nanoparticle/polymers systems for the case of bare and hydride palladium. Stability of palladium hydride nanoparticles is studied, as well as different types of interaction at the Pd-polymer interface. These results are then used to shed light on how the presence of polymers, and the existence of a palladium/polymer interface, can affect the kinetics and thermodynamics of the system in order to facilitate H2 adsorption and desorption processes. |
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L70.00393: The role of potassium on CO oxidation Bin Di Alkali metals are regarded as promoters in many catalysts which can promote the reaction rate of various chemical processes including ammonia synthesis, CO oxidation, the water-gas shift reaction and so on. However, an unambiguous picture of how alkali metals impact catalytic activity have not been draw. In order to uncover alkali-metals promotion effect, we focus on the chemical and physical properties of atomically dispersed alkali metal, such as atomic potassium, supported on ultrathin metal oxide film and the interaction of alkali metals with noble metals which possess catalytic activity for a range of chemical reactions. |
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L70.00394: Alkali Metals on Ultrathin Oxide Surface: A Low-Temperatrue STM research Zhantao Peng Alkali metal plays an important role in heterogeneous catalysis, semiconductor physics, superconducting physics and has received extensive attention in its adsorption behavior and electronic properties on both single crystal surface and oxide surface. In this report, a low-temperature scanning tunneling microscopy (LT-STM) is employed to investigate the behavior of alkali metal on ultrathin CuO surfaces. While the electronic properties of some transtional metals atoms on such an oxide surface can be dramaticly affected by the co-adsorption alkali metals. |
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L70.00395: Structure, magnetic properties, and thermal stability of chemically prepared nickel carbide nanoparticles Grant Lu, Jerome R Troy, Gerald R Poirier, Roddel Remy, Karl Unruh Single phase nickel carbide nanoparticles and phase separated nickel carbide/elemental nickel nanocomposites have been prepared by the reduction of nickel acetate in triethylene glycol at reduction temperatures between 250 and 290 ○C. The structure, magnetic properties, and thermal stability of these samples have been studied by x-ray diffraction (XRD), vibrating sample magnetometry (VSM), and differential scanning calorimetry (DSC) measurements. The XRD measurements indicate that the nickel carbide phase is hexagonal (S.G. 167) with lattice parameters of a=0.45908(1) and c=1.30080(3) nm; somewhat larger values than previously reported. The hexagonal phase has a room temperature magnetization of about 0.2 emu/g and a Curie temperature of about 330 ○C. At a heating rate of 10 ○C/min the hexagonal phase irreversible transforms to face-center-cubic elemental nickel starting at a temperature of about 380 ○C. |
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L70.00396: Collective cell migration induced by the interplay of contractile force and adhesion with delay under ERK signal propagation. Tatsuya Fukuyama, Hiroyuki Ebata, Yohei Kondo, Satoru Kidoaki, Kazuhiro Aoki, Yusuke T. Maeda Collective migration is ubiquitously observed in epithelial cell sheets during wound healing and morphogenesis. For epithelial MDCK cells, ERK MAP kinase forms solitary wave and propagate across migrating cells. Cells orient their directions of migration oppose to the ERK wave, however, their guidance is distinct from tactic behavior. To understand the underlying mechanism of ERK directed collective migration, we propose simple theoretical model where interplay of focal adhesion and contractile force is regulated by ERK signal. Given that ERK signal locally increases both contractile force and focal adhesion onto substrate, we construct the equation of force-balance between viscous cellular fluid and dissipative friction. When ERK signal moves in two-dimensional space, local gradients of enhanced contractile force and reduced friction make viscous cell body easily streamed. Then, the net motion of fluids occurs and its velocity is given by an analytical solution. We test theoretical result by using optogenetic control of cell migration and find that cells are steered opposite to synthetic ERK signal. Our finding, including optimal velocity of cell migration against ERK wave, suggests the guidance of collective migration is driven by dissipative mechanics of cells. |
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