Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session P1: Poster Session II (11:00 am - 2:00 pm) |
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Sponsoring Units: APS DPOLY/DBIO GSNP/GSOFT Room: Exhibit Hall C |
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P1.00001: SOFT CONDENSED MATTER |
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P1.00002: Slow Relaxations of Supercooled Water Determined by Energy Landscape Sampling Nathan Walter, Yang Zhang Molecular Dynamics simulations have been widely used to provide insight into atomistic scale materials behavior and to compare with neutron scattering experiments. However, such simulations are inhibited by temporal scale and spatial scale constraints. As a consequence, it is only possible to predict the dynamical behavior of materials at short times, while atomistic simulations beyond microsecond remain a challenge. The energy landscape sampling methods have been suggested to predict materials behavior at long times. Herein, we show that by efficiently sampling the activation barriers of the high-dimensional energy hypersurface we were able to study the slow dynamics of supercooled ST2 water down to deeply supercooled temperatures. Furthermore, the method allows us to quantify the statistics of the activation barriers, yielding insight into the slow and fast dynamics of ST2 water at low temperatures. The computed transport coefficients across a wide temporal range are useful to bridge the gap between neutron scattering experiments and other bulk measurements. [Preview Abstract] |
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P1.00003: Single-stranded DNA induced chirality and helical twist in achiral liquid crystals Rajratan Basu A small quantity of single-stranded DNA (Deoxyribonucleic acid$-$cellulose single-stranded from calf thymus DNA in lyophilized powder form) was doped in an achiral liquid crystal (LC), and the mixture was found to exhibit a weak degree of chirality. The induced chirality in the LC was probed by means of the electroclinic effect in the LC's smectic-A phase, which showed significant pretransitional behavior on approaching the smectic-$A$--smectic-$C$ transition temperature from above. The same DNA was doped in an achiral nematic LC and the mixture was found to exhibit an average mechanical twist over macroscopic dimensions. The single-stranded DNA-induced chiral pitch length $P$ was determined by measuring the radius of curvature of reverse twist disclination lines in 90$^{\mathrm{o}}$ nematic twist cells. In the LC$+$DNA mixture, the LC's benzene rings interact with the nucleobases of the DNA through $\pi -\pi $ stacking, which induces a molecular conformational deracemization in the LC. [Preview Abstract] |
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P1.00004: Local environment of iron in garden soil Vs Plants Sunil Dehipawala, Chaojung Dong, Stephen Smith, Patricia Schneider, Harry Gafney Iron is an essential nutrient not only for humans, but also for all types of plants. Plants use iron for chlorophyll formation, RNA metabolism, and transpiration process regulation. Iron is one of the most abundant metals in the soil and occurs in a wide range of chemical forms. The correlation between the iron species presents in soil and in \textbf{\textit{Petroselinum crispum}} (parsley) plants were investigated using the room temperature Mossbauer spectroscopy. Mossbauer spectrum of garden soil consists of two doublets. Based on the established isomer shift and quadrupole splitting values of iron, these doublets can be identified as due to octahedrally coordinated Fe$^{3+}$ and tetrahedrally coordinated Fe$^{2+}$. Most of the iron present in the parsley has the form Fe$^{3+}$ or electron density at the site of the iron nucleus similar to that of Fe$^{3+}$. These findings will help establish soil conditions necessary to increase Fe$^{2+}$ intake by plants similar to the form of iron present in most supplements. [Preview Abstract] |
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P1.00005: Chemotaxing and haptotaxing random walkers having directional persistence Tae Goo Kwon Biological cell crawling is a rather complex process involving various bio-chemical and bio-mechanical processes, many of which are still not well understood. The difficulties in understanding the crawling are originating not just from cell-intrinsic factors but from their complex social interactions, cell-to-substrate interactions and nonlinear responses toward extrinsic factors. Here, in this report we investigate chemotactic behavior of mathematical model cells that naturally have directional persistence. A cell density is measured as a function of time and space, then the resulting steady state is compared with that of the well-known Keller-Segal model, which describes a population of chemotactic random walker. Then, we add a cell-to-cell interaction, mimicking a ``haptotaxis'' mediated interaction, to the model and access its role as for altering the steady-state cell density profile. This mathematical model system, which we have developed and considered in this work, can be quite relevant to the chemotactic responses of interacting immune cells, like microglia, moving toward and around a site of wound, as for an example. We conclude by discussing some relevant recent experimental findings. [Preview Abstract] |
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P1.00006: Aqueous Foam Stabilized by Tricationic Amphiphilic Surfactants Seth Heerschap, John Marafino, Kristin McKenna, Kevin Caran, Klebert Feitosa The unique surface properties of amphiphilic molecules have made them widely used in applications where foaming, emulsifying or coating processes are needed. The development of novel architectures with multi-cephalic/tailed molecules have enhanced their anti-bacterial activity in connection with tail length and the nature of the head group. Here we report on the foamability of two triple head double, tail cationic surfactants (M-1,14,14, M-P, 14,14) and a triple head single tail cationic surfactant (M-1,1,14) and compare them with commercially available single headed, single tailed anionic and cationic surfactants (SDS,CTAB and DTAB). The results show that bubble rupture rate decrease with the length of the carbon chain irrespective of head structure. The growth rate of bubbles with short tailed surfactants (SDS) and longer, single tailed tricationic surfactants (M-1,1,14) was shown to be twice as high as those with longer tailed surfactants (CTAB, M-P,14,14, M-1,14,14). This fact was related to the size variation of bubbles, where the foams made with short tail surfactants exhibited higher polydispersivity than those with short tails. This suggests that foams with tricationic amphiphilics are closed linked to their tail length and generally insensitive to their head structure. [Preview Abstract] |
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P1.00007: Reversible mechano-memory in sheared cross-linked actin networks Sayantan Majumdar, Margaret L. Gardel Is it possible to control the shear modulus of a material mechanically? We reconstitute a network of actin filaments cross-linked with Filamin A and show that the system has remarkable property to respond under shear in a deformation history dependent manner. When a large shear stress pulse is applied to the system, the system remembers the direction of deformation long after the stress pulse is removed. For the next loading cycle, shear response of the system becomes anisotropic; if the applied pulse direction is same as the previous one, the system behaves like a viscoelastic solid but a transient liquefaction is observed if the pulse direction is reversed. Imaging and normal force measurements under shear suggest that this anisotropic response comes from stretching and bending dominated deformation directions induced by the large shear deformation giving rise to a direction dependent mechano-memory. The long time scale over which the memory effect persists has relevance in various deformations in cellular and multicellular systems. [Preview Abstract] |
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P1.00008: Understanding hydrodynamics in the cell at the molecular level Xiaoyu Bai, Peter Wolynes Cellular collective motion is a result of complex coupling of nonequilibrium mechano-chemical events in the cytoskeleton, of which the underlying physics is far from completely understood. In an attempt to study the cytoskeletal dynamics, we develop analytical theories based on a coarse-grained model, Cat's Cradle. Our current work highlights how the activated events due to energy-consuming molecular motors are coupled by hydrodynamic interaction and therefore reveals the modified cytoskeletal dynamics. Within our framework, we were able to find the stability limit of the uniformly flowing phase, which is consistent with the predictions from the well-studied continuum models. In the model we accounted for the effect of shear-stretching forces on the extended structure of molecular motors. The resulting influenced stochastic properties of motor power strokes provide us with further insights into the nonequilibrium aspects of cellular dynamics. [Preview Abstract] |
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P1.00009: Behavior of Caulobacter Crescentus Diagnosed Using a 3-Channel Microfluidic Device Jay Tang, Michael Morse, Remy Colin, Laurence Wilson Many motile microorganisms are able to detect chemical gradients in their surroundings in order to bias their motion towards more favorable conditions. We study the biased motility of Caulobacter crescentus, a singly flagellated bacteria, which alternate between forward and backward swimming, driven by its flagella motor, which switches in rotation direction. We observe the swimming patterns of C. crescents in an oxygen gradient, which is established by flowing atmospheric air and pure nitrogen through a 3 parallel channel microfluidic device. In this setup, oxygen diffuses through the PDMS device and the bacterial medium, creating a linear gradient. Using low magnification, dark field microscopy, individual cells are tracked over a large field of view, with particular interest in the cells' motion relative to the oxygen gradient. Utilizing observable differences between backward and forward swimming motion, motor switching events can be identified. By analyzing these run time intervals between motor switches as a function of a cell's local oxygen level, we demonstrate that C. crescentus displays aerotacitc behavior by extending forward swimming run times while moving up an oxygen gradient, resulting in directed motility towards oxygen sources. Additionally, motor switching response is sensitive to both the steepness of the gradient experienced and background oxygen levels with cells exhibiting a logarithmic response to oxygen levels. [Preview Abstract] |
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P1.00010: Influence of Chirality in Ordered Block Copolymer Phases Ishan Prasad, Gregory Grason Block copolymers are known to assemble into rich spectrum of ordered phases, with many complex phases driven by asymmetry in copolymer architecture. Despite decades of study, the influence of intrinsic chirality on equilibrium mesophase assembly of block copolymers is not well understood and largely unexplored. Self-consistent field theory has played a major role in prediction of physical properties of polymeric systems. Only recently, a polar orientational self-consistent field (oSCF) approach was adopted to model chiral BCP having a thermodynamic preference for cholesteric ordering in chiral segments. We implement oSCF theory for chiral nematic copolymers, where segment orientations are characterized by quadrupolar chiral interactions, and focus our study on the thermodynamic stability of bi-continuous network morphologies, and the transfer of molecular chirality to mesoscale chirality of networks. Unique photonic properties observed in butterfly wings have been attributed to presence of chiral single-gyroid networks, this has made it an attractive target for chiral metamaterial design. [Preview Abstract] |
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P1.00011: Jamming, Self-Filtration and Cake Growth in Concentrated Particle Suspensions Youjing Guo, Shoubo Li, Donglei Yang, Yongli Mi, Xiaorong Wang We study the flows of concentrated particle suspensions driven through a circular orifice. Above a critical concentration, a jammed structure (i.e., quasi-solid sphere) often forms in the flow and at the entrance of the geometrical constriction. Once occurred this jammed structure grows fast as time t passes and produces a reduction in the solid concentration downstream. Our analysis shows that a combination of the particle jamming, the self-filtration, and the cake-formation with the flow passing through the pores of the jammed solid is responsible for the occurrence of such phenomena. Based on this mechanism, we establish a mathematical model to show how the jammed structure is propagated. Our results suggest that the size D of the jammed structure in this case is proportional to a 1/3 power of the time t. Experiments also support this conclusion. [Preview Abstract] |
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P1.00012: Designing thermo-responsive nanocomposites with anti-fouling properties Ya Liu, Gerald McFarlin, Xin Yong, Olga Kuksenok, Anna Balazs Inspired by marine organisms that utilize active ``defense'' (such as active cilia) to prevent the biofouling of their surfaces, we use computational modeling to design synthetic gel-based composite films that provide dual ``defense'' for antifouling applications. We design a nanocomposite gel film that can be harnessed to repel a variety of particles via either a temperature change or an imposed shear. Incorporation of stiff hydrophobic posts into a gel composed of cross-linked poly(N-isoproylacrylamide) chains allows us to drastically alter the film's surface properties when gel undergoes temperature-induced volume phase transition. Depending on whether the system's temperature is below or above the lower critical solution temperature (LCST) of the gel, the posts are hidden in the swollen gel or exposed to the external solution. We model our system using dissipative particle dynamics (DPD); we validate our model through comparisons with Flory-Rehner theory. We focus on the influence of shear and temperature on the position of the particle in the system and isolate the conditions under which adsorption of particles of different sizes to the substrate is effectively prevented. [Preview Abstract] |
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P1.00013: Optically driven translational and rotational motions of micro-rod particles in a nematic liquid crystal Ralf Stannarius, Alexey Eremin, Hajnalka Nadasi, Hideo Takezoe, Pemika Hirankittiwong, Nattaporn Chattham, Osamu Haba, Koichiro Yonetake Liquid crystals are self-organized mesomorphic materials with various symmetries and structures. Their unique features can be exploited for smart multifunctional materials. Colloidal dispersions of micro- and nano-particles in LCs have been widely studied. We demonstrate controlled light-driven translational and rotational motions of micro-rods in a nematic matrix. A small amount of azo-dendrimer molecules dissolved in a liquid crystal drives translation and rotation under non-polarized UV light irradiation. This is initiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the rod surface and the associated director reorientation. This system represents an optically driven molecular microactuator, which exploits molecular reorientation on a particle surface and transforms it into a mechanical torque. [Preview Abstract] |
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P1.00014: Thermophoresis of micrometer-sized poly(N-isopropylacrylamide) microgel particles Kevin Aptowicz, Tim Still, Arjun Yodh We investigate the diffusion and thermodiffusion of micrometer sized poly(N-isopropylacrylamide) (PNIPAM) gel particles in a temperature gradient. Recently published results of the thermophoretic mobility of PNIPAM systems are puzzling. Cross-linked microgel particles show unusually large thermophoretic mobility whereas the mobility of core-shell colloids and linear polymers are more consistent with other aqueous systems. Our experiments add to our empirical understanding of thermophresis of PNIPAM particles. In particular, we study micrometer-sized PNIPAM particles, which are an order of magnitude larger than those previously studied. The size of the particles prohibits the use of optical beam deflection, the standard measurement technique. Instead, the thermophoretic mobility of the particles is measured using a novel optical system utilizing video microscopy and ring traps generated with holographic techniques. [Preview Abstract] |
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P1.00015: Nucleation Pathways of CO2 Condensation under Mesoporous Templated Glass Bo Wang, Matthew S. Byran, Garfield T. Warren, Paul E. Sokol Carbon capture and storage (CCS) are important elements in reducing greenhouse gas emission and combating global warming. The adsorption behavior of CO2 under mesoporous confinement at room temperature is particularly relevant. , Small Angle Scattering of X-ray (SAXS) and Neutron (SANS) were used to probe the adsorption process of CO2 under such mesoporous confinement MCM-41 and details of nucleation pathways were mapped out by fitting the scattering intensities with adsorption models. From both experiments, the nucleation of CO2 on the inner pore surface of MCM-41 is found to be a two-step process; high density liquid phase CO2 first forms uniform layers following the long range translational symmetry of the porous matrix, above one CO2 filling, determined by the pore size and temperature, capillary condensation initiates. The nucleation sites formed during capillary condensation start to separate the long range symmetry from the one at uniform layers. Finally, SAXS and SANS techniques are compared and they both showed their unique properties of probing the filling-dependent structures of adsorbed CO2 under such mesoporous system. [Preview Abstract] |
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P1.00016: Divergence of the Long Wavelength Collective Diffusion Coefficient in Quasi-one and Quasi-two Dimensional Colloid Suspensions Binhua Lin, Bianxiao Cui, Xinliang Xu, Ronen Zangi, Haim Diamant, Stuart A. Rice We report the results of experimental studies of the short time-long wavelength behavior of collective particle displacements in q1D and q2D colloid suspensions. Our results are reported via the $q$-\textgreater 0 behavior of the hydrodynamic function $H(q)$ that relates the effective collective diffusion coefficient, $D_{e}(q)$, with the static structure factor $S(q)$ and the self-diffusion coefficient of isolated particles $D_{o}$: $H(q) D_{e}(q) S(q)$/$ D_{o}$. We find an apparent divergence of $H(q)$ as $q$-\textgreater 0 with the form H(q)q$^{-}$(1.7 \textless $\gamma $\textless 1.9), for both q1D and q2D colloid suspensions. Given that $S(q)$ does not diverge as we infer that $D_{e}(q)$ does. This behavior is qualitatively different from that of the three-dimensional $H(q)$ and $D_{e}(q)$ as $q$-\textgreater 0, and the divergence is of a different functional form from that predicted for the diffusion coefficient in one component 1D and 2D fluids not subject to boundary conditions that define the dimensionality of the system. [Preview Abstract] |
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P1.00017: Predicting and measuring the effects of colloid polydispersity during spinodal decomposition John Williamson, R. Mike L. Evans Polydispersity pervades soft matter physics, but remains so poorly understood that its effects are often guessed at or ignored entirely. Significant progress has been made on the phase equilibria of polydisperse colloids, but practical understanding of the kinetics that govern real systems lags behind. We employ Kinetic Monte Carlo simulation to study the gas-liquid spinodal decomposition of a size-polydisperse colloid, particularly focusing on fractionation (demixing) between the phases, an effect which causes the properties of the ``daughter'' phases to depart significantly from the overall ``parent'' particle distribution. We find that intricate fractionation takes place from the earliest times, so can play a role even in arrested, far-from-equilibrium states (e.g. gels). Novel techniques (in principle applicable to experiment) are developed to detect fractionation: a parameter-free method of systematically coarse-graining local volume fraction; and several spatial correlation functions. The qualitative features of fractionation, including a striking dependence on inter-particle potential, are correctly predicted by a theory requiring only a monodisperse reference free energy.\\[4pt] References: JJW and RMLE J. Chem. Phys. 141 (2014), Phys. Rev. E. 86 (2012). [Preview Abstract] |
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P1.00018: Cooperative dynamics in ultrasoft 2D crystals Joris Sprakel, Berend van der Meer, Marjolein Dijkstra, Jasper van der Gucht The creation, annihilation, and diffusion of defects in crystal lattices play an important role during crystal melting and deformation. Although it is well understood how defects form and react when crystals are subjected to external stresses, it remains unclear how crystals cope with internal stresses. We report a study in which we create a highly localized internal stress, by means of optical tweezing, in a crystal formed from micrometer-sized colloidal spheres and directly observe how the solid reacts using microscopy. We find that, even though the excitation is highly localized, a collective dance of colloidal particles results; these collective modes take the form of closed rings or open-ended strings, depending on the sequence of events which nucleate the rearrangements. Surprisingly, we find from Brownian Dynamics simulations that these cooperative dynamics are thermally-activated modes inherent to the crystal, and can even occur through a single, sufficiently large thermal fluctuation, resulting in the irreversible displacement of 100s of particles from their lattice sites. [Preview Abstract] |
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P1.00019: ABSTRACT WITHDRAWN |
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P1.00020: Determination of colloidal particle surface charge from dielectrophoresis Marko Chavez, Rittirong Nuansri, Jacob Mazza, H. Daniel Ou-Yang Electrophoresis (EP) is used to determine colloidal particle surface charge. However, when the Debye length is comparable to or larger than the particle size, electrophoresis cannot be reliably used to determine the surface charge due to counter ion retardation flow. Alexander et al. developed a theory relating colloidal osmotic pressure and particle surface charge. We use dielectrophoresis (DEP) to obtain a potential landscape based on the number density distribution of the particles in a non-uniform AC electric field. We determine the osmotic pressure from the DEP force and density profiles using Einstein's osmotic equilibrium equation. Surface charge obtained by DEP (thermodynamics) will be compared to that obtained by EP (electrokinetics). [Preview Abstract] |
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P1.00021: Fabrication of Uniform Janus Micorparticles by Photopolymerization-Driven Phase Separation and their Asymmetric Hybridization with Metal Nanoparticles Jangwoo Cho, Jeong Won Kim, Jin Woong Kim In the field of colloid science, there is growing interest in synthesis of anisotropic particles, since they are desirable for controlling light scattering. These anisotropic particles have been developed by using sophisticated techniques, including clusterization, stamping, microfluidics, and controlled nucleation and precipitation. This study introduces a facile approach for fabrication of uniform Janus microparticles with anisotropic phases as well as selected surface chemistry. The technique we employed to synthesize these microparticles was the seeded swelling and polymerization method, in which complete compartmentalization of the particles into two distinct phases occurred upon polymerizing the monomer-swollen droplets. Then, we patched nanoparticles, such as gold nanoparticles and magnetic nanoparticles, onto one of the compartmentalized phases of the Janus microparticles. Finally we demonstrate that these asymmetrically hybridized Janus microparticles are of great importance and play a role in the designated colloidal 2D array. [Preview Abstract] |
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P1.00022: Fabrication of Uniform Hydrogel Microparticles with Alternate Polyelectrolyte/Silica Shell Layers for Applications of Controlled Loading and Releasing Eun Sook Jeong, Jin Woong Kim Hydrogel particles, also known as microgels, consist of cross-linked three-dimensional water-soluble polymer networks. They play an essential role in loading and delivering active ingredients in medicine, cosmetics, and foods. Despite their excellent biocompatibility as well as structural diversity, much wider applications are limited due mainly to their intrinsically loose network nature. This study introduces a practical and straightforward method that enables fabrication of hydrogel microparticles layered with a mechanically robust hybrid thin shell. Basically highly monodisperse hydrogel microparticles were produced in microcapillary devices. Then, their surface was coated with alternate polyelectrolyte layers through the layer-by-layer deposition. Finally a thin silica layer was again formed by reduction of silicate on the amino-functionalized polyelectrolyte layer. We have figured out that these hybrid hydrogel microparticles showed controlled loading and releasing behaviors for water-soluble probe molecules. Moreover, we have demonstrated that they can be applied for immobilization of biomacromolecules, such as bacteria and living cells, and even for targeted releasing. [Preview Abstract] |
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P1.00023: 2D Colloidal Wigner crystals in confined geometries Ruben Higler, Joris Sprakel Crystallization of bulk systems has been widely studied using colloids as a model system. However, study into colloidal crystallization in confined geometries has been sparse and little is known about the effects of strong confinement on the dynamics of colloidal crystal. In our research we prepare 2D crystals from charged colloids in an apolar solvent to study crystal dynamics, formation, and structure in circular confinements. These confining geometries are made using softlithography techniques from SU-8. In order to broaden the parameter space we can reach in experiments we employ brownian dynamics simulations to supplement our experimental results. Using single-particle tracking we have subpixel resolution positional information of every particle in the system. We study the vibrational modes of our confined crystals and find well defined modes unique to confined systems, such as a radially symmetric compression (or breathing) mode, a collective rotation mode, and distinct resonance modes. Furthermore, due to the circular nature of our constrictions, defectless crystals are impossible, we find, for sufficiently high area fractions, that the defects order at well defined points at the edge. The effect of this ``defect-localization'' has a clear influence on the vibrational modes. [Preview Abstract] |
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P1.00024: Shear-induced demixing of glassy suspension Ties van de Laar, Joris Sprakel, Karin Schroen The ground state of a binary suspension composed of particles of incommensurate size is that of two demixed crystal phases. However this has never been experimentally observed, due to the prohibitively long time scales associated with diffusion in a glass. Here we show that enhancing particle mobility in a glass, by means of flow, can lead to this type of solid-solid demixing. We study this phenomenon at the scale of single particles by means of high speed confocal imaging of suspensions flowing through microfluidic channels. By systematically varying the applied pressures and volume fractions we intend to bridge the gap between classical shear-induced migration at dilute concentrations and deformation of glasses. [Preview Abstract] |
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P1.00025: Hyperuniformity of self-assembled soft colloidal spheres Coline Bretz, Ye Xu, Tim Still, Jean Baudry, Lawrence A. Hough, Arjun G. Yodh, Salvatore Torquato, Remi Dreyfuss Hyperuniformity characterizes a state of matter for which density fluctuations vanish on large scales. Hyperuniform materials are of technological importance as they exhibit interesting photonic properties. We have shown that such materials can be obtained by assembling spheres into a disordered jammed 2D- packing. To this end, we use a binary mixture of large and small Poly(NIPAM) particles confined between two cover slips. These soft spheres have been chosen for their temperature-sensitive properties. We can locally increase or decrease the volume fraction occupied by the spheres by finely tuning the temperature. By applying various temperature patterns, we are studying the spatial arrangements of the microgels and characterizing their hyperuniform properties through reconstruction and detection algorithms. [Preview Abstract] |
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P1.00026: Model colloidal system for interfacial adsorption kinetics Steven Hudson, Paul Salipante An experimental colloidal model for sorption behavior may allow direct observation of the effects of particle shape and concentration on adsorption and desorption kinetics. Here we investigate spherical colloid adsorption to near a solid surface. The attraction is induced by depletion interaction. The colloid-interface interaction potential is tuned to be less than 10 k$_{\mathrm{B}}$T using a combination of depletion, electrostatic, and gravitational forces. The colloids transition between an entropically trapped adsorbed state and a desorbed state through Brownian motion. High resolution particle tracking is made using LED-based Total Internal Reflection Microscopy (TIRM). The observed adsorption and desorption rates obey different distributions and are compared to theoretical predictions based on the measured interaction potential and near wall particle diffusivity. This experimental system also allows for the study of more complex dynamics such as nonspherical colloids and collective effects at higher concentrations. [Preview Abstract] |
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P1.00027: ABSTRACT WITHDRAWN |
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P1.00028: Interfacial Behavior of Polymer Coated Nanoparticle Luqing Qi, Hadi shamsijazeyi, Jason Mann, Rafael Verduzco, George Hirasaki Oxidized carbon black (OCB) nanoparticle is functionalized with different coatings, i.e. alkyl group, polyvinyl alcohol (PVA) and partially sulfonated polyvinyl alcohol (sPVA). In oil and water systems, the functionalized nanoparticle is found to have a versatile dispersion i.e. in lower aqueous phase, in upper oil phase, or in middle phase microemulsion. Oil substitute n-octane and commercial oil IOSPAR have been test as oil phase; series of commercially available surfactant, C12-4,5 orthoxylene sulfonate(OXS), i-C13-(PO)7 --SO4Na (S13B), surfactant blend of anionic Alfoterra with nonionic Tergitol have been test as additive to help with the OCB dispersion. It is found that the OCB with sulfonated polyvinyl alcohol attachment (sPVA-OCB) stays in microemulsion; with the increase of salinity, it follows the microemulsion to go from lower phase, to middle phase, and to upper phase. The dispersion of sPVA and alkyl functionalized OCB (Cn-OCB-sPVA) is the balance of the length of alkyl and sPVA and the degree of sulfonation of PVA, depending on which, it can either disperse into microemulsion or form a separate layer. The sPVA-OCB also indicates a tolerance of high salinity; this is shown by the stable dispersion of it in blend surfactant solution of anionic Alfoterra and nonionic Tergitol at high salinity API brine( 8{\%} NaCl and 2{\%} CaCl2). The study of different functionality on OCB dispersion can help design appropriate modified nanoparticle as additive for enhanced oil recovery either to reduce the interfacial tension between oil and water, or to stabilize microemulsion. [Preview Abstract] |
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P1.00029: Nematic Liquid Crystal reorientation with a Photosensitive layer Adrian Reyes, Laura Palomares, Patricia Gutierrez We assume a nematic cell in a planar configuration for which one of their confining plates, is submitted to a hard-anchoring boundary condition and the other plate has a coating monolayer of azo dye molecules, such that the change of the orientation of azo dye isomers, due to light, causes changes in the nematic director. We find an approximated expression for the density of isomers, written in terms of the director angle, which allows us to close the equation for the director's angle on the boundary having a photosensitive plate. We have managed to decouple the director's angle and the isomer densities by assuming extremely different temporal time scales between them. We show that switching times inversely depend on trans-cis transition rate of photo-excitation meanwhile relaxation times do not depend on it, for a given sample. On the other hand, switching and relaxation times linearly depend on surface viscosity values. [Preview Abstract] |
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P1.00030: Electric field variation within a nematic liquid crystal layer Linda Cummings, Ensela Mema, Chenjing Cai, Lou Kondic A thin layer of Nematic Liquid Crystal (NLC) across which an electric field is applied is a setup of great industrial importance in Liquid Crystal Display devices, and there is a wide associated literature. A common assumption is that an electric field generated by constant-potential electrodes at the two bounding surfaces of the layer will produce a field that is uniform: the presence of NLC does not affect the electric field. We derive the equations that couple the electric potential to the orientation of the NLC's director field and use asymptotic and computational methods to address the question: Under what conditions is the uniform field assumption justified, and when is it inappropriate?\\[4pt] [1] Cummings, L.J., Mema, E., Cai. C, and Kondic, L. Electric field variation within a nematic liquid crystal layer, \emph{Phys. Rev. E - Stat. Nonlin. and Soft Matter Phys.}, 90, 2014. [Preview Abstract] |
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P1.00031: Molecular dynamics simulations of liquid crystalline ordering in bulk and at interfaces Xiaoyu Wei, Justin Hooper, Dmitry Bedrov The influence of induced polarization interactions in atomistic MD simulations on the thermodynamic and structural properties of 4-Cyano-4'-pentylbiphenyl (5CB) bulk systems have been systematically investigated utilizing both polarizable (POL) and non-polarizable (NP) version of the APPLE{\&}P force field (FF). The predicted densities for the nematic and isotropic phases of 5CB are in excellent agreement with available experimental data. However, the nematic-isotropic transition temperature T$_{\mathrm{NI}}$ showed noticeable sensitivity to the details of FF. The NP FF showed a tendency to predict systematically higher T$_{\mathrm{NI}}$ (by about 30K) and showed very little sensitivity to modifications of dihedral potential in the biphenyl unit. The POL FF showed a much stronger sensitivity to the details of biphenyl conformational properties and was able to predict T$_{\mathrm{NI}}$ at around 313K, which is very close to the experimental T$_{\mathrm{NI}}$ of 308K. Using the developed potentials we have also investigated the anchoring of nematic 5CB at the water interface as well as phase behavior and structure of the newly discovered twist-bend nematic phase of CB7CB. Detailed analysis of molecular scale correlations for both systems will be presented and discussed in light of available experimental data. [Preview Abstract] |
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P1.00032: Polarized Raman Spectroscopic and Conoscopic study of twist-bend nematic liquid crystal CB7CB Jinxin Fu, Karthik Nayani, Jung Ok Park, Mohan Srinivasarao The liquid crystal CB7CB, which exhibits a new twist bend nematic phase, has aroused lots of interest recently. We use polarized Raman Spectroscopy to measure the liquid crystal order parameters, which are crucial to know the molecular orientation distribution and to understand the phase transition. It is found that in the twist-bend phase, both P\textless 200\textgreater and P\textless 400\textgreater increase with temperature before the nematic transition takes place at 103$^{\circ}$C, and then decrease in the nematic region until the LC becomes isotropic at 116$^{\circ}$C. Conoscopy is a convenient tool to determine the structure and orientation of crystals. We develop a monochromatic conoscopy method to study the uniaxial and biaxial behavior of CB7CB in the different phases. [Preview Abstract] |
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P1.00033: Ground states of lyotropic chromonic liquid crystals in cylindrical capillaries Rui Chang, Karthik Nayani, Jinxin Fu, Elsa Reichmanis, Jung Ok Park, Mohan Srinivasarao We investigate the ground states of nematic lyotropic chromonic liquid crystals (LCLCs) confined in cylindrical capillaries. Two line defects with double helical configuration is observed for Sunset Yellow FCF with the homeotropic anchoring being obtained by parylene-N coating. The striking features of nematic-isotropic phase transition is also studied, in which we find a coexistence of double helix configuration and escape radial configuration mediated with point defects in biphasic temperature range. However with Disodium Cromoglycate (DSCG) we observe that the anchoring is planar anchoring in both parylene-N coated and uncoated borosilicate capillaries. [Preview Abstract] |
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P1.00034: ABSTRACT WITHDRAWN |
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P1.00035: Lipid Nanodiscs as potential carriers of enzymes: a light scattering study Kiril Streletzky, Ghaith Tawalbeh, Mekki Bayachou The structure and dynamics of discoidal phospholipid protein complexes (nanodiscs) with and without endothelial nitric oxide synthase (eNOS) were studied with multiangle polarized and depolarized light scattering. Nanodiscs present a mobile system that is similar to enzyme's native microenvironment which allows to explore the potential effect of membrane phospholipids on the activity of eNOS. Light scattering revealed at least two different size distribution modes for empty nanodiscs, and nanodiscs loaded with eNOSoxy. In both cases, the first mode was diffusive (linear $\Gamma$ vs q$^2$ with a small intercept) with apparent Rh$=$ 4.5 nm for empty nanodiscs and 4.9nm for loaded nanodisc, sizes consistent with nanodisc dimensions. The second mode contributed only about 20\% to the intensity and showed non-diffusive behavior which might correspond to coalesced nanodiscs present in solution. Studied concentration dependencies and depolarized scattering measurements on enzyme free and enzyme loaded nanodiscs corroborated these findings. Also, the specific activity of nanodiscs-bound eNOS was found to be significantly lower than the specific activity of free eNOS. [Preview Abstract] |
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P1.00036: Active motion induced break-up of colloidal gels Megan Szakasits, Michael Solomon We found that fractal gel networks of polystyrene colloids can be broken up by active motion of Janus colloids that have been incorporated into them. Janus particles were synthesized by electron beam deposition of platinum onto one micron carboxylate modified polystyrene particles. Through addition of the divalent salt magnesium chloride, an initially stable suspension of Janus and polystyrene colloids, present in equal proportion, underwent aggregation to yield a fractal gel. The Janus colloids were activated by addition of 30{\%} v/v hydrogen peroxide through a porous hydrogel membrane. Changes in structure and dynamics were visualized by two channel confocal laser scanning microscopy (CLSM). By means of image analysis, we calculated the mean squared displacement (MSD) and radial distribution function (RDF) for gel samples before and after addition of hydrogen peroxide. The MSD confirmed the Janus particles we synthesized undergo active motion. The RDF and cluster size distribution of gel samples before and after addition of peroxide demonstrate how active motion broke apart the gel network into smaller clusters. [Preview Abstract] |
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P1.00037: Direct visualization of photoinduced glassy dynamics on the amorphous silicon carbide surface by STM movies Duc Nguyen, Lea Nienhaus, Richard T. Haasch, Joseph Lyding, Martin Gruebele Glassy dynamics can be controlled by light irradiation. Sub- and above-bandgap irradiation cause numerous phenomena in glasses including photorelaxation, photoexpansion, photodarkening and pohtoinduced fluidity. We used scanning tunneling microscopy to study surface glassy dynamics of amorphous silicon carbide irradiated with above- bandgap 532 nm light. Surface clusters of $\sim$ 4-5 glass forming unit in diameter hop mostly in a two-state fashion, both without and with irradiation. Upon irradiation, the average surface hopping activity increases by a factor of 3. A very long ($\sim$1 day) movie of individual clusters with varying laser power density provides direct evidence for photoinduced enhanced hopping on the glass surfaces. We propose two mechanisms: heating and electronic for the photoenhanced surface dynamics. [Preview Abstract] |
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P1.00038: A Simulation Study on Translation-Rotation Decoupling and its Dependence on Tracer Shape in Two Dimensional Colloids Jeongmin Kim, Bong June Sung Near the glass transition, translation is often faster than expected from the viscosity of liquids unlike rotation. It is the well-known translation-rotation decoupling phenomenon. In this poster, we present the dependence of the decoupling on tracer shape in two-dimensional (2D) colloids using three representative tracer shapes (diamond, distorted diamond and square). We find that near the freezing (liquid-hexatic) transition, the translation-rotation decoupling occurs for all tracers regardless of shapes, but trends are different for different shape. In 2D, there exists an orientationally ordered liquid phase called a hexatic phase between isotropic liquid and solid phases. Entering the hexatic phase, 2D colloids exhibit the heterogeneous dynamics with several dynamic regions of different mobility like glass-forming liquids [1]. We find that the observed decoupling of tracer diffusion is attributed to the dynamic heterogeneity of 2D colloids. To our surprise, the shape-dependence of decoupling trend relate closely to the rotational diffusion of tracers. Square shape tracer disturbs the hexagonal ordering of 2D colloids, thus resulting in faster rotation of square tracers, which is not observed for diamond shape tracers. \\[4pt] [1] J. Kim, C. Kim, B. J. Sung, Phys. Rev. Lett. 110, 047801 (2013) [Preview Abstract] |
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P1.00039: Trimerization of Phenyl Cyanate Ester Madhusudhan Reddy Pallaka, Sindee L. Simon The kinetics of phenyl cyanate ester trimerization is studied in the bulk using differential scanning calorimetry. Dynamic experiments for different heating rates are analyzed for the activation energy using the model-free Kissinger-Akahira-Sunose(KAS) isoconversion method. The activation energy and other kinetic parameters are also obtained by fitting the dynamic data to a first order autocatalytic reaction model, which well describes the experimental data. The activation energy obtained from the KAS isoconversion method (70.1 kJ/mol) is in good agreement with that obtained from the kinetic model (73.2 kJ/mol) and is much lower than the more bulky cyanate esters studied in our laboratory, which have activation energies of approximately 95 kJ/mol. In addition, the rate constant for the phenyl cyanate ester is one to two orders higher than the bulkier cyanate esters in the temperature range of 200 to 300$^{\circ}$C. Further elucidation of the dynamic experiments revealed a strong dependence of the reaction kinetics on the sample weight. Future work aims to understand this finding. [Preview Abstract] |
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P1.00040: FEL approach to the crystallization of super-cooled liquids Takashi Odagaki, Anju Okada The crystallization time of most super-cooled liquids as a function of temperature (time-temperature-transformation (TTT) diagram) show a nose-shaped form, namely near the melting temperature it is an increasing function of temperature and at much lower temperatures it becomes a decreasing function of temperature. The former behavior is believed to be controlled by the thermodynamics and the latter is governed by the slow dynamics. Exploiting the merit of the free energy landscape (FEL) approach which can handle both thermodynamic and dynamic processes in the same frame work, we investigate the crystallization of super-cooled liquids as the first passage process of a representative point to the crystalline basin in the FEL. We first show that the crystallization time can be related to the eigenvalues of the transition matrix which governs the stochastic dynamics of the representative point in the FEL. We apply this formalism to various structures of the FEL which include the small world and the scale free network. We show that the TTT diagram is sensitive to the structure of the FEL, indicating the possibility of obtaining the structural information from the TTT diagram. [Preview Abstract] |
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P1.00041: Critical adsorption and colloidal interaction in binary liquid mixtures Sharmine Alam, Rami Omari, Christopher Grabowski, Ashis Mukhopadhyay We studied critical adsorption on colloidal nanoparticles in binary liquid mixture of 2,6 lutidine $+$ water by using fluorescence correlation spectroscopy (FCS). Our results indicated that the adsorbed film thickness is of the order of correlation length associated with concentration fluctuations. The excess adsorption per unit area increases following a power law in reduced temperature with an exponent of -1, which is the mean-field value for the bulk susceptibility exponent. The measurements at higher particle volume fractions, where particle-particle interaction becomes important, will be presented. [Preview Abstract] |
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P1.00042: Control of nanoparticle formation using the constrained dewetting of polymer brushes Thomas Lee, Shaun C. Hendy, Chiara Neto We have used coarse-grained molecular dynamics simulations to investigate the use of pinned micelles formed by the constrained dewetting of polymer brushes to act as a template for nanoparticle formation. The evaporation of a thin film containing a dissolved solute from a polymer brush was modeled to study the effect of solubility, concentration, grafting density, and evaporation rate on the nucleation and growth of nanoparticles. Control over particle nucleation could be imposed when the solution was dilute enough such that particle nucleation occurred following the onset of constrained dewetting. We predict that nanoparticles with sizes on the order of 1 nm to 10 nm could be produced from a range of organic molecules under experimentally accessable conditions. This method could allow the functionality of organic materials to be imparted onto surfaces without the need for synthetic modification of the functional molecule, and with control over particle size and aggregation, allowing for the preparation of surfaces with useful optical, pharmaceutical, or electronic properties. [Preview Abstract] |
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P1.00043: STATISTICAL AND NON LINEAR PHYSICS |
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P1.00044: Critical behavior of the disordered three-color Ashkin-Teller Model -- A Monte Carlo study Qiong Zhu, Xin Wan, Rajesh Narayanan, Jos\'{e} A. Hoyos, Thomas Vojta The impact of quenched disorder on systems undergoing first-order phase transitions has received less attention than its effects on critical points. A notable exception is the seminal work by Aizenmann and Wehr\footnote{M. Aizenman and J. Wehr, PRL 62, 2503 (1989).}. Building on earlier work by Imry, Ma and others, they rigorously proved the vanishing of latent heat in dimensions $d\leq 2$ in the presence of quenched disorder. In this context, we numerically study the critical behavior of a three-color Ashkin Teller (AT) model in the presence of bond randomness. The clean AT model is known to exhibit a fluctuation-driven first-order transition. An analytical renormalization group treatment by Cardy\footnote{J. Cardy, J. Phys. A 29, 1897 (1996).} predicted that disorder rounds this transition and leads to a critical point in the clean Ising universality class. However, recent numerical work\footnote{A. Bellafard et al, PRL 109, 155701 (2012).} has questioned the veracity of these results. We therefore use Monte-Carlo techniques to re-examine the role of quenched disorder on the three-color AT model. We determine the order of the phase transition, and we perform a systematic finite-size scaling analysis of various thermodynamic quantities to extract the critical behavior. [Preview Abstract] |
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P1.00045: Hysteretic transitions in the Kuramoto model with inertia Alessandro Torcini, Simona Olmi, Adrian Navas, Stefano Boccaletti We report finite size numerical investigations and mean field analysis of a Kuramoto model with inertia for fully coupled and diluted systems. In particular, we examine the transition from incoherence to coherence for increasingly large system size and inertia. For sufficiently large inertia the transition is hysteretic and within the hysteretic region clusters of locked oscillators of various sizes and different levels of synchronization coexist. A modification of the mean field theory developed by Tanaka, Lichtenberg, and Oishi allows to derive the synchronization curve associated to each of these clusters. We have also investigated numerically the limits of existence of the coherent and of the incoherent solutions. The minimal coupling required to observe the coherent state is largely independent of the system size and it saturates to a constant value already for moderately large inertia values. The incoherent state is observable up to a critical coupling whose value saturates for large inertia and for finite system sizes, while in the thermodinamic limit this critical value diverges proportionally to the mass. By increasing the inertia the transition becomes more complex, and the synchronization occurs via the emergence of clusters of coherently drifting oscillators. [Preview Abstract] |
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P1.00046: Discontinuous phase transitions via cooperative contagion Fakhteh Ghanbarnejad, Weiran Cai, Li Chen, Peter Grassberger We study the spreading of two diseases that interact cooperatively (the presence of one helps the other one to spread) on different network topologies, and with two microscopic realizations, both of which are stochastic versions of an SIR type studied by us recently in mean field approximation. We had shown that cooperativity can lead to discontinuous transitions (DT). However, due to the rapid mixing implied by the mean field assumption, DTs were seen only when there were finite (non-zero) densities of sick individuals in the initial state.In this paper we find that the results for the stochastic model depend strongly on the underlying network. In particular, DTs are found when there are few short but many long loops: (i) No DTs exist on trees, due to the absence of loops; (ii) On 2-d lattices with local contacts there are no DTs either, but because of too many short loops; (iii) We do find DTs on Erdos-Renyi (ER) networks, on d-dimensional lattices with $d\geq 4$,and on 2-d lattices with sufficiently long-ranged contacts; (iv) On 3-d lattices with local contacts the results depend on the microscopic details of the implementation. All found discontinuous transitions are of ``hybrid" type, i.e. they display also scaling features usually associated with continuous transitions. [Preview Abstract] |
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P1.00047: ABSTRACT WITHDRAWN |
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P1.00048: Origin of the $1/f^{\alpha}$-Spectral-Noise in Chaotic and Regular Quantum Systems Leonardo A. Pachon, Armando Rela\~no, Borja Peropadre, Alan Aspuru-Guzik Based on the recent connection between the spectral form factor and the probability to return [Phys. Rev. Lett. 102, 150401 (2009)], the origin of the $1/f^\alpha$-noise in fully chaotic and fully integrable systems is tracked to the quantum interference between invariant manifolds of the classical dynamics and the dimensionality of those manifolds. This connection and the order-to-chaos transition are analyzed in terms of the statistics of Floquet's quasienergies of a classically chaotic driving non-linear system. The direct connection established here allows for predicting that in the presence of decoherence, the statistics of the spectral correlations of both, chaotic and integrable, coincide. [Preview Abstract] |
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P1.00049: Enhanced rare-region effects in the contact process with long-range correlated disorder Ahmed K. Ibrahim, Hatem Barghathi, Thomas Vojta We investigate the nonequilibrium phase transition in the disordered contact process in the presence of long-range spatial disorder correlations. These correlations greatly increase the probability for finding rare regions that are locally in the active phase while the bulk system is still in the inactive phase. Specifically, if the correlations decay as a power of the distance, the rare-region probability is a stretched exponential of the rare-region size rather than a simple exponential as is the case for uncorrelated disorder. As a result, the Griffiths singularities are enhanced and take a non-power-law form. The critical point itself is of infinite-randomness type but with critical exponent values that differ from the uncorrelated case. We report large-scale Monte Carlo simulations that verify and illustrate our theory. We also discuss generalizations to higher dimensions and applications to other systems such as the random transverse-field Ising model, itinerant magnets, and the superconductor-metal transition. [Preview Abstract] |
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P1.00050: Critical Initial Slip Scaling for Driven-dissipative Bose-Einstein Condensation Weigang Liu, Uwe Tauber We investigate the universal non-equilibrium critical behavior at the driven- dissipative Bose-Einstein condensation phase transition by means of the perturbative field-theoretic renormalization group method. Such criticality may be realized experimentally in driven open systems on the interface of quantum optics and many-body physics, ranging from exciton--polariton condensates in optically pumped semiconductor wells to cold atomic gases. We describe the critical dynamics through a noisy and dissipative Gross- Pitaevski or time-dependent Ginzburg-Landau equation with complex coefficients. We focus on the universal critical behavior of this system in the early stages of the relaxation process following a quench from an initially (Gaussian distributed) disordered state that is characterized by broken time translation invariance and governed by the ``initial slip'' exponent $\theta $. We compute $\theta $ to first order in the dimensional $\varepsilon = $ 4 -- d expansion with respect to the upper critical dimension d$=$4, and find that its one-loop value is identical to that of the classical relaxational model A for a two-component non-conserved order parameter. [Preview Abstract] |
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P1.00051: Energy flow between two hydrodynamically coupled particles kept at different effective temperatures Sergio Ciliberto, Antoine Berut, Artyom Petrosyan We measure the energy exchanged between two hydrodynamically coupled micron-sized Brownian particles trapped in water by two optical tweezers. The system is driven out of equilibrium by random forcing the position of one of the two particles. The forced particle behaves as it has an ``effective temperature'' higher than that of the other bead. This driving modifies the equilibrium variances and cross-correlation functions of the bead positions: we measure an energy flow between the particles and an instantaneous cross-correlation, proportional to the effective temperature difference between the two particles. A model of the interaction which is based on classical hydrodynamic coupling tensors is proposed. The theoretical and experimental results are in excellent agreement. [Preview Abstract] |
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P1.00052: Effect of Graphene in Quenching Fluorescence from Strained Conjugated Polymer Doped Polystyrene Composite Films Xuan Long Ho, Yan-Hao Chen, Jonathon David White, Nen-Wen Pu, Arnold Chang-Mou Yang Introduction of graphene into films and solutions of conjugated polymers has been observed to dramatically quench photoluminescence (PL) of MEH-PPV. In other work, the PL of MEH-PPV well dispersed in an optically inert matrix was seen to be dramatically increased when the individual molecular strands were fully stretched. Strong polarization effects indicated that stretching individual polymer chains was responsible for the observed enhancement. We examine the combined effect of stress and the addition of reduced graphene oxide (rGO) on PL. We found that the addition of a small amount of rGO (0.3{\%}) into polystyrene films lightly doped with 1{\%} MEH-PPV quenched 40{\%} of the PL. Stretching resulted in the creation of local deformation zones (LDZ) of high stress and strain. Within these zones, while the PL efficiency increased dramatically for all films, the effect was greatest for those incorporating rGO. We conclude that the application of stress on the conjugated polymers reduces charge transfer between the polymer and the graphene flakes.~ [Preview Abstract] |
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P1.00053: Mechanical Properties of Hydrogel Beads Keely Criddle, Thomas Benns, Dan Shorts, Klebert Feitosa Fragile solids made of dense disordered packing of bubbles, droplets and grains are able to withstand small stresses by virtue of system-wide force chains that lock the system into a jammed state. The nature of the jamming transition in such soft materials has been the subject of intense research, but despite much effort, a deep understanding remains elusive. In this experiment we study the mechanical properties of hydrogel beads to exploit them as force transducers in densely packed systems. The experiment consists of applying uniaxial planar compressions on the beads, and correlating the force to the bead's strain and contact area. The results show that while the strain scales linearly with the diameter of the contact area, the force and strain are found to obey a power law relation with two distinct exponents at small and large strains. This result leads to a power law dependence of the force on the contact area diameter of the compressed bead. [Preview Abstract] |
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P1.00054: The nature of long-ranged forces between pinned particles in a jammed system Juan-Jose Lietor-Santos, Justin Burton We explore the interaction between of two fixed-position particles immersed in a binary, two-dimensional jammed system of disks at T$=$0. In our simulations, the two pinned particles develop an interaction along their alignment direction. At short distances, their interaction can be described by a mean-force potential derived from the particle-particle correlation function, g(r), and thus have a repulsive and attractive nature which depends on separation. However, there is an additional repulsive force that dominates at large particle separation or when the ambient jammed disks are much smaller than the pinned particles. We will show that the nature of this repulsive force stems from fluctuations near the jamming transition, in analogy with other fluctuation-induced forces, such as the thermal Casimir effect. We expect these results will be relevant to other studies of pinned particles near the glass transition [1]. The dependence of the long-ranged force on packing fraction, particle separation, and the size ratio of pinned to free particles will be discussed. \\[4pt] [1] C. Cammarota and G. Biroli. PNAS 109, 8850-8855, (2012). [Preview Abstract] |
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P1.00055: ``Anti-Equilibrium'': The limiting frozen state of kappa distributions George Livadiotis The kappa distribution of particle velocities provides an unambiguous replacement of the Maxwell distribution for systems out of thermal equilibrium. The kappa index is a measure of how far the system of particles is from thermal equilibrium. This ``thermodynamic distance'' is inversely proportional to the kappa index; it becomes zero at thermal equilibrium where the kappa index is infinite, while it obtains its maximum at the furthest state from thermal equilibrium, where the kappa index is zero, a state called ``anti-equilibrium.'' By keeping fixed the temperature and decreasing the kappa index, the particles approach this peculiar state of anti-equilibrium and are characterized by a power-law distribution density with spectral index $\sim$ 1.5; this constitutes a universal behavior, independent of the system's number of particles or degrees of freedom. As the kappa decreases and the system approaches the anti-equilibrium state, the particles lose their kinetic energy. This procedure of ``kappa-freezing'' by decreasing the kappa index at a fixed temperature is similar to the more familiar freezing procedure of decreasing temperature and approaching the ``absolute zero'' for a fixed kappa index. [Preview Abstract] |
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P1.00056: The price of anarchy is maximized at the percolation threshold Brian Skinner When many independent users try to route traffic through a network, the flow can easily become suboptimal as a consequence of congestion of the most efficient paths. The degree of this suboptimality is quantified by the so-called ``price of anarchy'' (POA), but so far there are no general rules for when to expect a large POA in a random network. Here I address this question by introducing a simple model of flow through a network with randomly-placed ``congestible'' and ``incongestible'' links. I show that the POA is maximized precisely when the fraction of congestible links matches the percolation threshold of the lattice. Both the POA and the total cost demonstrate critical scaling near the percolation threshold. [Preview Abstract] |
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P1.00057: Four Parameter Characterization of Network Reliability and Analysis of Critical Point Phenomenology Madhurima Nath, Stephen Eubank, Mina Youssef, Yasamin Khorramzadeh, Shahir Mowlaei A new characterization of network structure as represented by the reliability polynomial is introduced that requires only four parameters. Exact evaluation of the polynomial is not feasible for large graphs. Approximation to within a specified error is feasible, but a complete specification of the polynomial still requires many parameters. However, it turns out that a two-parameter family of functions fits the non-trivial part of the reliability polynomial to within approximation error. We demonstrate this by fitting the reliability polynomials of both random graphs with different sizes and synthetic social networks to the error function. The network reliability can be viewed as a partition function of a physical system, for example percolation on a network. This method produces a good analytical approximation to the partition function for a given network and suggests a way to explore critical point phenomenology. [Preview Abstract] |
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P1.00058: Diffusion theory of Brownian particles moving at constant speed in \textit{D} dimensions Francisco J. Sevilla The propagation of Brownian-active particles that move at constant speed in the limit of short times, differs from wave-like propagation in that active particles propagate without leaving a wake trailing characteristic of wave propagation in even dimensions. In the long time regime, normal diffusion is expected due to random fluctuations that disperse the particle direction of motion. A phenomenological equation that describe the transition from the behavior free of effects of wake, to the normal diffusion of the particles is proposed. A comparison of the results predicted by such equation with those obtained from models using Langevin equations is presented in the spherically symmetric case. [Preview Abstract] |
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P1.00059: ABSTRACT WITHDRAWN |
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P1.00060: Nature of the Congested Traffic and Quasi-steady States of the General Motor Models Bo Yang, Xihua Xu, John Z.F. Pang, Christopher Monterola We look at the general motor (GM) class microscopic traffic models and analyze some of the universal features of the (multi-)cluster solutions, including the emergence of an intrinsic scale and the quasisoliton dynamics (arXiv:1407.3177). We show that the GM models can capture the essential physics of the real traffic dynamics, especially the phase transition from the free flow to the congested phase, from which the wide moving jams emerges (the F-S-J transition pioneered by B.S. Kerner). In particular, the congested phase can be associated with either the multi-cluster quasi-steady states, or their more homogeneous precursor states. In both cases the states can last for a long time, and the narrow clusters will eventually grow and merge, leading to the formation of the wide moving jams. We present a general method to fit the empirical parameters so that both quantitative and qualitative macroscopic empirical features can be reproduced with a minimal GM model. We present numerical results for the traffic dynamics both with and without the bottleneck, including various types of spontaneous and induced ``synchronized flow,'' as well as the evolution of wide moving jams. We also discuss its implications to the nature of different phases in traffic dynamics. [Preview Abstract] |
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P1.00061: New Analysis Techniques for Avalanches in a Conical Bead Pile with Cohesion Catherine Tieman, Susan Lehman Avalanche statistics and pile geometry for 3~mm steel spheres dropped on a conical bead pile were studied at different drop heights and different cohesion strengths. The pile is initially built on a circular base and is subsequently slowly driven by adding one bead at a time to the apex of the pile. We investigate the dynamic response of the pile by recording avalanches off the pile over the course of tens of thousands of bead drops. The level of cohesion is tuned through use of an applied uniform magnetic field. Changes in the pile mass and geometry were investigated to determine the effect of cohesion and drop height on the angle of repose. The angle of repose increased with cohesion strength, and decreased somewhat for higher drop heights. The packing density of beads is expected to decrease as magnetic cohesion increases, but for our 20~000-bead pile, this effect has not been observed. The proportion of beads removed from the pile by different avalanche sizes was also calculated. Although larger avalanches are much rarer occurrences, they carry away a larger fraction of the total avalanched mass than small avalanches. As the pile cohesion increases, the number of small and medium avalanches decreases so that this mass loss distribution shifts more strongly to large sizes. [Preview Abstract] |
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P1.00062: Use of a magnetic field to modify and detect avalanche behavior on a conical bead pile Nathan Johnson, Susan Lehman A conical bead pile subject to slow driving and an external magnetic field is used to test the effects of drop height and cohesion on avalanche statistics. Magnetically susceptible beads were dropped onto a pile from different heights and into different strengths of magnetic field. Avalanches were recorded by the change in mass as beads fall off the pile. For beads dropped from a low drop height with no cohesion, the avalanche size distribution follows a power law. As cohesion increases, we observe an increase in the probability of very large avalanches and decreases in the mid-size avalanches. The resulting bump in the avalanche distribution moves to larger avalanche size as the cohesion in the system is increased, matching the prediction by an analytic theory from a mean-field model of slip avalanches. The model also makes predictions for avalanche duration, which is not measurable with our current system. Since the steel beads are magnetized while in the applied magnetic field, their motion during an avalanche creates a change in magnetic flux. To detect this motion, we have placed a large-diameter pick-up coil around the pile. Results of the testing and calibration of this coil to measure avalanche duration are presented. [Preview Abstract] |
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P1.00063: Granular gas mediated attraction of intruders in a granular Casimir effect George Wilkes, Brian Utter When two objects are submerged in a granular gas, entropic effects due to inelastic collisions lead to attractions between the objects. This has been referred to as an analog to the Casimir effect, though arises via a different mechanism. In this experiment, we place two objects (such as vertical plates or spheres) in either a strongly driven granular gas or dense fluid. We find that when the plates are closely spaced, there is a net attractive force. By analyzing high-speed video, we track the distance between these plates and characterize the effective force versus distance with changes in the vibration parameters and initial separation. A 2D simulation is also used to further explore parameter space. [Preview Abstract] |
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P1.00064: Fingering in Confined Elastic Layers John Biggins, L. Mahadevan, Z. Wei, Baudouin Saintyves, Elizabeth Bouchaud Fingering has recently been observed in soft highly elastic layers that are confined between and bonded to two rigid bodies. In one case an injected fluid invades the layer in finger-like protrusions at the layer's perimeter, a solid analogue of Saffman-Taylor viscous fingering. In a second case, separation of the rigid bodies (with maintained adhesion to the layer) leads air to the formation of similar fingers at the layer's perimeter. In both cases the finger formation is reversible: if the fluid is removed or the separation reduced, the fingers vanish. In this talk I will discuss a theoretical model for such elastic fingers that shows that the origin of the fingers is large-strain geometric non-linearity in the elasticity of soft solids. Our simplified elastic model unifies the two types of fingering and accurately estimates the thresholds and wavelengths of the fingers. [Preview Abstract] |
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P1.00065: Non-equilibrium relaxation between two quasi-stationary states in a stochastic lattice Lotka-Volterra model Sheng Chen, Uwe C. T\"{a}uber Spatially extended stochastic models for predator-prey competition and coexistence display complex, correlated spatio-temporal structures and are governed by remarkably large fluctuations. Both populations are characterized by damped erratic oscillations whose properties are governed by the reaction rates. Here, we specifically study a stochastic lattice Lotka-Volterra model by means of Monte Carlo simulations that impose spatial restrictions on the number of occupants per site. The system tends to relax into a quasi-stationary state, independent of the imposed initial conditions. We investigate the non-equilibrium relaxation between two such quasi-stationary states, following an instantaneous change of the predation rate. The ensuing relaxation times are measured via the peak width of the population density Fourier transforms. As expected, we find that the initial state only influences the oscillations for the duration of this relaxation time, implying that the system quickly loses any memory of the initial configuration. [Preview Abstract] |
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P1.00066: Implications of lack-of-ergodicity in 2D Potts model Smita Ota Microcanonical Monte Carlo simulation is used to study two dimensional (2D) q state Potts model. We consider a 2D square lattice having NxN spins with periodic boundary condition and simulated the system with N$=$15 and q$=$10. The demon energy distribution is found to be exponential for high system energy and large system size. For smaller system size and above the first order transition the demon energy distribution is found to deviate from exp(-$\beta $E$_{D})$ and has the form exp(-$\beta $E$_{D}+\gamma $E$_{D}^{2})$. Here $\beta =$1/k$_{B}$T and k$_{B}$ is the Boltzmann constant. It is found that $\gamma $ is finite at higher temperatures. As the system energy is reduced $\gamma $ becomes zero near the first order transition. It is found that during cooling $\gamma $ changes sign from negative to positive and then to negative again near the 1$^{st}$ order transition. Therefore the demon energy distribution becomes exp(-$\beta $E$_{D})$ (or ergodic) at two values of system energy near the 1$^{st}$ order transition. Further cooling or at still lower temperatures the system shows lack of ergodicity. However, difference in heating cooling curves are apparent in E vs $\gamma $. The system energies for which $\gamma $ is zero during cooling can represent the 'ergodic' states. This can be related to the two-level systems observed in glasses at low temperatures. [Preview Abstract] |
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P1.00067: DIGIT-PHYSICS: Digits Are Bosons Are Quanta Because (On Average) Quanta and Bosons Are and Always Were Digits!!! DIGITS?: For a Very Long Time Giving Us All The FINGER!!! Edward Carl-Ludwig Siegel, Simon Newcomb, John William Strutt-Rayleigh, Henri Poincare, Hermann Weyl, Frederick Benford, Marvin Antonoff DIGIT-PHYSICS: DIGITS?: For a Very Long Time Giving Us All The FINGER!!!: CONTRA Wigner,``On the Unreasonable Effectiveness of Physics in Mathematics!''; A Surprise in Theoretical/Experimental Physics and/or Ostensibly Pure-Mathematics: PHYSICS: Quantum-Mechanics/Statistical-.Mechanics. DIGITS-LAW(S); DIGITS' ostensibly ``pure-mathematics' 1:1-map onto the QUANTUM!!! [Google:''http://www.benfordonline.net/ list/ chronological'']: Newcomb[Am.J.Math.4,39(1881)]-Poincare[Calcul des Probabilit\'{e}(1912)]-Weyl[Math.Ann., 77, 313(1916)-Benford[J.Am.Phil Soc,78,115 (1938)]-..-Antonoff/Siegel[AMS Joint-Mtg.,San Diego(2002)-abs.{\#} 973-60-124] empirical inter-digit\textbraceleft on-ANY/ALL averageS) \textless P(d) \textgreater $=$ log[base$=$10] (1 $+$ 1/d) $=$ log[base$=$10] ([d$+$1]/d) upon algebraic-inversion is d $=$ 1/[10\textasciicircum [\textless P\textgreater ] -1] \textasciitilde 1/[2.303..e\textasciicircum [\textless P\textgreater ] -1] \textasciitilde 1/[2.303..e\textasciicircum [\textless $\omega $\textgreater ] -1] \textasciitilde 1/[2.303..e\textasciicircum [$\omega $] -1]: Digits Are Bosons Are Quanta Because (On Average) Quanta and Bosons Are and Always Were Digits!!! (Ex: atom energy-levels numbering: 0,\textellipsis ,9) ANY/ALL QUANTUM-physics[Planck(1901)-Einstein(1905)-Bose(1924)-Einstein(1925)-vs.Fermi(1927)-Dirac(1927)-\textellipsis ] is and always was Newcomb(1881) DIGIT-physics!!! [Preview Abstract] |
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P1.00068: Static and Dynamic Finite-Size Scaling for Kuramoto Model with Generalized Form of Unimodal Natural Frequency Distribution Chulho Choi, Hyunggyu Park Synchronization phase transitions of collective phase oscillators have been studied actively for decades. The natural frequency distribution $g(\omega)$ of oscillators plays an important role in determination the phase transition's types, properties and its universality class. Kuramoto model, a basic framework for synchronization, with unimodal and symmetric natural frequency distribution exhibits a second-order phase transition with critical exponent $\beta=1/2$ whereas uniform distribution or bimodal and symmetric distribution make it a first-order phase transition, i.e., $\beta=0$. We present a case in which $\beta$ has other values than 1/2 or 0 even though it still has a unimodal natural frequency distribution and generalize it to obtain any values of $\beta$ as we want. Therefore, we need to describe the unimodalness more precisely. As a result, the critical exponent $\bar{\nu}$ and dynamic exponent $\bar{z}$ also have different values than the known values. We derive those exponents analytically and confirm them using static and dynamic finite-size scaling in numerical simulation. [Preview Abstract] |
(Author Not Attending)
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P1.00069: Signatures of the Berezinskii-Kosterlitz-Thouless transition on the zeros of the canonical partition function for the 2D XY-model Julio Rocha, Lucas Mol, Bismarck Costa In this work we show that the canonical partition function zeros, the Fisher zeros, can be used to uniquely characterize a transition as being in the Berezinskii-Kosterlitz-Thouless (BKT) class of universality. By studying the zeros map for the 2D XY model we found that its internal border coalesces into the real positive axis in a finite region corresponding to temperatures smaller than the BKT transition temperature. This behavior is consistent with the predicted existence of a line of critical points below the transition temperature, allowing one to distinguish the BKT class of universality from other ones. [Preview Abstract] |
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P1.00070: Nonlinear dynamics of three gravitating rods Ziyi Sang, John Lindner As a generalization of Newton's three body problem, we explore the dynamics of three massive line segments interacting gravitationally. The extension of each line segment or slash (/) provides extra degrees of freedom that enable the interplay between rotation and revolution in an especially simple example while still elucidating the dynamics of non spherical objects like asteroids and space stations. Fortunately, Newton's laws imply exact algebraic expressions for the force and torque between the slashes, and this greatly facilitates analysis of this slash-slash-slash (///) body problem. We provide exact solutions to several symmetrical orbits and numerically study three slashes moving in a figure-8 orbit. [Preview Abstract] |
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P1.00071: Balancing Newtonian gravity and spin to create localized structures Michael Bush, John Lindner Using geometry and Newtonian physics, we design localized structures that do not require electromagnetic or other forces to resist implosion or explosion. In two-dimensional Euclidean space, we find an equilibrium configuration of a rotating ring of massive dust whose inward gravity is the centripetal force that spins it. We find similar solutions in three-dimensional Euclidean and hyperbolic spaces, but only in the limit of vanishing mass. Finally, in three-dimensional Euclidean space, we generalize the two-dimensional result by finding an equilibrium configuration of a spherical shell of massive dust that supports itself against gravitational collapse by spinning isoclinically in four dimensions so its three-dimensional acceleration is everywhere inward. These Newtonian ``atoms'' illuminate classical physics and geometry. [Preview Abstract] |
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P1.00072: BIOLOGICAL PHYSICS |
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P1.00073: Single-molecule optical study of cholesterol-mediated dimerization process of EGFRs in different cell lines Chien Yu Lin, Jung Y. Huang, Leu-Wei Lo A growing body of data reveals that the membrane cholesterol molecules can alter the signaling pathways of living cells. However, the understanding about how membrane cholesterol modulates receptor proteins remains lacking. In this study we applies single-molecule optical tracking on ligand-induced dimerization process of EGFRs in the plasma membranes of several cancer and normal cell lines. We tracked individual EGFR and dual correlated receptors in the plasma membranes of live cells. We developed an energetic model based on the generalized Langevin equation and the Cahn-Hilliard equation to help extracting information from single-molecule trajectories. From the study, we discovered that ligand-bound EGFRs move from non-raft areas into lipid raft domains. This ligand-induced motion is a common behavior for all cell lines under study. By manipulating the total amount of cholesterol with methyl-$\beta$-cyclodextrin and the local concentration of cholesterol with nystatin, we found that the amount of cholesterol can affect the stability of EGFR dimers. The EGFR dimers in the plasma membrane of normal cells are more sensitive to the local concentration changes of cholesterol than EGFR dimers in the cancer cells. [Preview Abstract] |
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P1.00074: Conformational transitions of plasmid ds-DNA on ultrathin films of alkylamines on graphite Caroline Falk, Hua Liang, Nikolai Severin, Wei Zhuang, Stefan Zauscher, J\"urgen P. Rabe DNA replication is an important process in the human body. Replication of double-stranded (ds)-DNA requires its local melting into two single strands [1]. DNA, when stretched in solution, overwinds and melts [2]. This was argued to give insight onto the replication mechanism. It is difficult, however, to access the direct conformational changes during stretching in solution. Recent work demonstrated that this transition can be imaged with scanning force microscopy on a graphite surface that is coated with an alkylamine layer [3]. ds-DNA can be controlled by an amphiphilic layer, since the DNA conformation depends on the amphiphile concentration. In particular we analyzed different DNA lengths on the same surface, and we found that at a specific concentration of octadecylamine the ds-DNA pUC19 plasmid ring splits into two single strands at one position. We will discuss methods to mark the DNA to determine the exact location at which the plasmid ring splits.\\[4pt] [1] D. Coman, I.M. Russu, J. Biol. Chem. 280 (2005) 20216.\\[0pt] [2] J. Adamcik, S. Tobenas, G. Di Santo, D. Klinov, G. Dietler, Langmuir 25 (2009) 3159.\\[0pt] [3] H. Liang, N. Severin, W. Zhuang, J.P. Rabe, Control of plasmid DNA Conformations on Molecularly Modified Graphene Surfaces (submitted). [Preview Abstract] |
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P1.00075: Modification of protein structure and function using photoactivated porphyrin ligands Gabriel Moreno The tremendous advances in genomic research have sparked an interest in investigating the possibility to ``manipulate'' the structure of proteins that modify existing functionality. This study makes use of small molecules (e.g., porphyrins) to photosensitize proteins and modify the higher order structure of the polypeptide with the goal of engineering novel functions, or affecting/eliminating native functions. The irradiation of non-covalently bound ligands prompts charge transfer events that have the potential to locally modify the structure of the host protein. The characterization of photoinduced conformational changes in the protein/porphyrin complex is carried out using a combination of electronic spectroscopy and kinetics (e.g., fluorescence spectroscopy, fluorescence decay, circular dichroism). This study is focused primarily on human serum albumin (HSA) as a model. The structure of HSA is well established, the binding sites for an array of ligands are well characterized (including one for protoporphyrins), and HSA provides a series of functions (including some allosteric activity) that can be tested. [Preview Abstract] |
(Author Not Attending)
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P1.00076: Bacterial Chemotaxis with a Moving Target Corey Dominick Most chemotaxis studies so far have been conducted in a quiescent fluid with a well-defined chemical gradient. Such experiments may be appropriate for studying enteric bacteria, such as \textit{Escherichia coli}, but the environment it provides is very different from that typically encountered by marine bacteria. Herein we describe an experiment in which marine bacterium \textit{Vibrio alginolyticus}is subject to stimulation by a small moving target. A micropipette of the tip size \textless 1 ?m is used to slowly release a chemoattractant, serine, at different concentrations. The pipette is made to move with different patterns and speeds, ranging from 0 to 100 ?m/s; the latter is about twice the bacterial swimming speed. We found that if the pipette is moved slowly, with 1/4 of bacterial swimming speed, cells accumulate near the tip region but when it is moved with speed greater than 1/2 the bacterial swimming speed, cells trail behind the pipette over a large distance. The behaviors observed in \textit{V. alginolyticus}are significantly different from \textit{E. coli}, suggesting that the former is a better chemotaxer in a changing environment. [Preview Abstract] |
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P1.00077: Bacterial Growth in Weak Magnetic Field Samina Masood We study the growth of bacteria in a weak magnetic field. Computational analysis of experimental data shows that the growth rate of bacteria is affected by the magnetic field. The effect of magnetic field depends on the strength and type of magnetic field. It also depends on the type of bacteria. We mainly study gram positive and gram negative bacteria of rod type as well as spherical bacteria. Preliminary results show that the weak magnetic field enhances the growth of rod shape gram negative bacteria. Gram positive bacteria can be even killed in the inhomogeneous magnetic field. [Preview Abstract] |
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P1.00078: Phase Transitions in the Nucleus: the functional implications of concentration-dependent assembly of a Liquid-like RNA/Protein Body Lian Zhu, Stephanie Weber, Joel Berry, Nilesh Vaidya, Mikko Haataja, Clifford Brangwynne The nucleolus is a liquid-like membrane-less nuclear body which plays an important role in cell growth and size control. By modulating nucleolar component concentration through RNAi conditions that change \textit{C. elegans} cell size, we find that nucleoli only assemble above a threshold concentration; moreover, the ripening dynamics of nucleated droplets are consistent with the hypothesis that the assembly of the nucleolus represents an intracellular liquid-liquid phase transition. A key question is how this phase-transition is linked to the primary function of the nucleolus, in transcribing and processing ribosomal RNA. To address this, we characterize the localization of RNA Polymerase I, a key transcriptional enzyme, into nucleolar foci as a function of nucleolar component concentration. Our results suggest that there are a small number of key disordered phosphoproteins that may serve as a link between transcription and assembly. Finally, we present preliminary results using a reduced model system consisting of purified nucleolar proteins to assess the ability of nucleolar proteins to drive liquid-liquid phase separation in vitro. These results lay the foundation for a quantitative understanding of intracellular phase transitions and their impact on biomedically-critical RNA-processing steps. [Preview Abstract] |
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P1.00079: Kinesin-1 Translocation along Human Breast Cancer Cell Microtubules \textit{in Vitro} Mitra Shojania Feizabadi, Yonggun Jun A principle approach to better understand intra-cellular microtubule based transport is to study such it \textit{in vitro}. Such \textit{in vitro} examinations have predominantly used microtubules polymerized from bovine brain tubulin, but motor function can also in principle be affected by the specific tubulin isotypes present in different cells. The human breast cancer cells carry different beta tubulin isotype distribution. However, it is entirely unknown whether transport along the microtubules is different in these cells. In this work we have characterized, for the first time, the translocation specifications of kinesin-1 along human breast cancer cell microtubules polymerized \textit{in vitro}. We found that as compared with the translocation along bovine brain microtubules, kinesin-1 shows a fifty percent shorter processive run length and slightly slower velocity under similar experimental conditions. These first time results support the regulatory role of tubulin isotypes in regards to motor protein translocations, and quantify the translocation specifications of kinesin-1 along microtubules of human breast cancer cells. [Preview Abstract] |
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P1.00080: Dissipative Dynamics of Enzymes Amila Ariyaratne, Chenhao Wu, Chiao-Yu Tseng, Giovanni Zocchi We explore enzyme conformational dynamics at sub - $\AA$ resolution, specifically temperature effects. The ensemble averaged mechanical response of the folded enzyme is viscoelastic in the whole temperature range between the warm and cold denaturation transitions. The dissipation parameter $\gamma$ of the viscoelastic description decreases by a factor 2 as the temperature is raised from 10 C to 45 C; the elastic parameter $K$ shows a similar decrease. Thus when probed dynamically, the enzyme softens for increasing temperature. Equilibrium mechanical experiments with the DNA spring (and a different enzyme) also show, qualitatively, a small softening for increasing temperature. [Preview Abstract] |
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P1.00081: Effects of solvent (effective medium versus explicit) on the structure of a protein (H3.1) Ras Pandey, Barry Farmer Structure and dynamics of a histone (H3.1) are studied in the presence of effective medium and explicit solvent over a range of temperatures with coarse-grained Monte Carlo simulations. The protein is represented by a coarse-grained chain of residues whose interactions are described by knowledge-based residue-residue and hydropathy-index-based residue-solvent interactions. Each empty lattice site acts as a solvent in effective medium while a fraction of sites are occupied by mobile solvent constituents in explicit solvent medium. The presence of fluctuations with explicit solvent may affect the structure and dynamics of protein differently than that in effective solvent medium. Large scale simulations are performed to analyze the structure of the protein for a range of residue-solvent interactions and temperature, and a number of local and global physical quantities are analyzed. Differences due to type of solvent on the response of some of these quantities as a function of temperature will be presented. [Preview Abstract] |
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P1.00082: ABSTRACT WITHDRAWN |
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P1.00083: ABSTRACT WITHDRAWN |
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P1.00084: Effect of Nanodiamond Surfaces on tRNA Dynamics Studied by Neutron Scattering and MD Simulations Gurpreet Dhindsa, Debsindhu Bhowmik, Panchapakesan Ganesh, Monojoy Goswami, Vadym N. Mochalin, Hugh O'Neill, Yury Gogotsi, Eugene Mamontov, Xiang Qiang Chu Nanodiamond (ND) inherits most of the superior properties of bulk diamond and delivers them at the nanoscale. ND is non-toxic and possesses excellent mechanical and optical properties with large surface area and surface functionality. ND mixed with biomolecules can be a good platform for drug delivery. Here we demonstrate the adsorption of tRNA on the ND surface and investigate the change in the tRNA dynamics using neutron scattering technique and molecular dynamics (MD) Simulations. We compare the dynamics of hydrated tRNA on ND surfaces with that of freestanding hydrated tRNA molecules and dry tRNA on ND surfaces. Both experiments and simulations show that the relaxational dynamics of tRNA on ND surface is faster than that of the freestanding tRNA molecules and dry tRNA on ND surfaces. Our results suggest that the tRNA on the ND surfaces has fewer hydration water molecules on it due to the water adsorption on the ND hydrophilic surface. Therefore fewer hydrogen bonds formed on its surface results in the tRNA faster motion. The MD simulations also show a ``caged'' dynamics of the water molecules adsorbed on the ND surfaces. [Preview Abstract] |
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P1.00085: Fast loop modeling for protein structures Jiong Zhang, Son Nguyen, Yi Shang, Dong Xu, Ioan Kosztin X-ray crystallography is the main method for determining 3D protein structures. In many cases, however, flexible loop regions of proteins cannot be resolved by this approach. This leads to incomplete structures in the protein data bank, preventing further computational study and analysis of these proteins. For instance, all-atom molecular dynamics (MD) simulation studies of structure-function relationship require complete protein structures. To address this shortcoming, we have developed and implemented an efficient computational method for building missing protein loops. The method is database driven and uses deep learning and multi-dimensional scaling algorithms. We have implemented the method as a simple stand-alone program, which can also be used as a plugin in existing molecular modeling software, e.g., VMD. The quality and stability of the generated structures are assessed and tested via energy scoring functions and by equilibrium MD simulations. The proposed method can also be used in template-based protein structure prediction. [Preview Abstract] |
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P1.00086: Bio-inspired metal-coordination dynamics: A unique tool for engineering novel properties in soft matter systems Scott Grindy, Qiaochu Li, Abigail Halim, Robert Learsch, Niels Holten-Andersen In soft material systems, materials properties are generally governed by transient, dynamic interactions of many types over many hierarchal length- and time-scales. However, explicit control over these dynamics is not always possible, leaving open questions into how transient interactions can be exploited to design soft materials with unique and exceptional properties. Inspired by the adhesive chemistry and tough character of mussel byssal threads, we present several studies on both the mechanical properties of soft materials and templated crystallization kinetics to show the diverse array of materials properties that can be generated using bio-inspired metal-coordination. By studying our model systems, we can determine the explicit effects of metal-coordination dynamics on various bulk properties, further adding to the set of tools we can use to design soft material systems. [Preview Abstract] |
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P1.00087: Examining the role of finite reaction times in swarming models Katherine Copenhagen, David Quint, Ajay Gopinathan Modeling collective behavior in biological and artificial systems has had much success in recent years at predicting and mimicing real systems by utilizing techniques borrowed from modelling many particle systems interacting with physical forces. However unlike inert particles interacting with instantaneous forces, living organisms have finite reaction times, and behaviors that vary from individual to individual. What constraints do these physiological effects place on the interactions between individuals in order to sustain a robust ordered state? We use a self-propelled agent based model in continuous space based on previous models by Vicsek and Couzin including alignment and separation maintaining interactions to examine the behavior of a single cohesive group of organisms. We found that for very short reaction times the system is able to form an ordered state even in the presence of heterogeneities. However for larger more physiological reaction times organisms need a buffer zone with no cohesive interactions in order to maintain an ordered state. Finally swarms with finite reaction times and behavioral heterogeneities are able to dynamically sort out individuals with impaired function and sustain order. [Preview Abstract] |
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P1.00088: High Intensity Pressure Noise Transmission in Human Ear: A Three Dimensional Simulation Study Takumi Hawa, Rong Gan, Kegan Leckness High intensity pressure noise generated by explosions and jet engines causes auditory damage and hearing loss of the military service personals, which are the most common disabilities in the veterans. Authors have investigated the high intensity pressure noise transmission from the ear canal to middle ear cavity. A fluid-structure interaction with a viscoelastic model for the tympanic membrane (TM) as well as the ossicular chain has been considered in the study. For the high intensity pressure simulation the geometry of the ear was based on a 3D finite element (FE) model of the human ear reported by Gan et al. (Ann Biomed Eng 2004). The model consists of the ear canal, TM, ossicular chain, and the middle ear cavity. The numerical approach includes two steps: 1) FE based finite-volume method simulation to compute pressure distributions in the ear canal and the middle ear cavity using CFX; and 2) FE modeling of TM and middle ear ossicles in response to high intensity sound using multi-physics analysis in ANSYS. The simulations provide the displacement of the TM/ossicular chain and the pressure fields in the ear canal and the middle ear cavity. These results are compared with human temporal bone experimental data obtained in our group. [Preview Abstract] |
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P1.00089: Computational Characterization of Type I collagen-based Extra-cellular Matrix Long Liang, Christopher Allen Rucksack Jones, Daniel Lin, Yang Jiao, Bo Sun A model of extracellular matrix (ECM) of collagen fibers has been built, in which cells could communicate with distant partners via fiber-mediated long-range-transmitted stress states. The ECM is modeled as a spring-like fiber network derived from skeletonized confocal microscopy data. Different local and global perturbations have been performed on the network, each followed by an optimized global Monte-Carlo (MC) energy minimization leading to the deformed network in response to the perturbations. In the optimization, a highly efficient local energy update procedure is employed and force-directed MC moves are used, which results in a convergence to the energy minimum state 20 times faster than the commonly used random displacement trial moves in MC. Further analysis and visualization of the distribution and correlation of the resulting force network reveal that local perturbations can give rise to global impacts: the force chains formed with a linear extent much further than the characteristic length scale associated with the perturbation sites and average fiber length. This behavior provides a strong evidence for our hypothesis of fiber-mediated long-range force transmission in ECM networks and the resulting long-range cell-cell mechanical signaling. [Preview Abstract] |
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P1.00090: Hidden Markov models for the analysis of single particle trajectories containing multiple mobile states Dylan Young, Jan Scrimgeour Single particle tracking offers significant insight into the molecular mechanics that govern the behavior of living cells. The analysis of trajectories that transition between different motive states, such as diffusive, driven and tethered modes, is of considerable importance, with even single trajectories containing significant amounts of information about a molecule's environment and its interactions with structures such as the cell cytoskeleton, membrane or extracellular matrix. Traditional analysis of particle trajectories has relied heavily on evaluation of the mean squared displacement, but often struggles to extract information reliably from small quantities of data or when multiple mobile states are present. Here, we present hidden Markov models for the analysis of complex multi-mobility tracks, focusing on transitions between states exhibiting free diffusion and either driven or tethered motion. The models were tested using simulated trajectories and practical limitations on the track length and state switching probabilities needed for accurate extraction of the physical parameters in the model are identified. These results provide critical information for the design of particle tracking experiments where trajectories containing multiple mobile states are expected. [Preview Abstract] |
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P1.00091: A theoretical analysis of inferring molecular interactions from single particle trajectories Ziya Kalay Single molecule/particle tracking has become a valuable tool in microscopy that allows for recording trajectories of probes such as individual biological molecules with high temporal and spatial resolution. With the trajectory of a particle, mesoscale transport properties such as diffusion coefficients and first-passage times can be calculated. With the trajectories of two particles that interact, we can investigate the kinetics of reactions by analyzing the statistics of overlap between trajectories. This approach is useful for single molecule biophysics in exploring the kinetics of reversible binding among molecules in biological membranes and on the DNA. Nevertheless, extracting information from noisy trajectories, where the noise stems from a combination of thermal fluctuations and uncertainty introduced by measuring apparatus, is a challenging task. In this work, we consider an exactly solvable model of diffusion and reversible binding in a 1-D structure, such as the DNA, and present a mathematical analysis of how much information about the binding kinetics can be reliably extracted from experimental data. With insight gained from this low-dimensional model, we discuss the analysis of trajectory pairs in two-dimensional systems such as biological membranes. [Preview Abstract] |
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P1.00092: Stochastic Movement of Multiple Motor Transported Cargo David Ando, Ajay Gopinathan, Jing Xu Experimental observations of cargo position during transport by multiple motors are determined by several coupled stochastic processes. During collective transport, each motor can transition between multiple kinetic states, with the state of each motor influencing the states of the others via mechanical coupling through a common cargo. We measured the motion of a micron sized bead as it is transported by two kinesin motors along a single microtubule track, focusing on cargo displacements which are both axial and transverse to the microtubule. We model the effects of inter-motor interference and the state of each motor throughout time, and back out motor properties using a systematic comparison of experimental observations with simulated model traces over a wide parameter space. Our model captures a surface-associated mode of kinesin, which is only accessible via inter-motor interference in groups, in which kinesin diffuses along the microtubule surface and rapidly ``hops'' between protofilaments without dissociating from the microtubule. This enhances local exploration of the microtubule surface, possibly enabling cellular cargos to overcome macromolecular crowding and to navigate obstacles along micro- tubule tracks without sacrificing overall travel distance. [Preview Abstract] |
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P1.00093: Light, Imaging, Vision: An interdisciplinary undergraduate course Philip Nelson The vertebrate eye is fantastically sensitive instrument, capable of registering the absorption of a single photon, and yet generating very low noise. Using eyes as a common thread helps motivate undergraduates to learn a lot of physics, both fundamental and applied to scientific imaging and neuroscience. I'll describe an undergraduate course, for students in several science and engineering majors, that takes students from the rudiments of probability theory to the quantum character of light, including modern experimental methods like fluorescence imaging and F\"orster resonance energy transfer. After a digression into color vision, we then see how the Feynman principle explains the apparently wavelike phenomena associated to light, including applications like diffraction, subdiffraction imaging, total internal reflection and TIRF microscopy. Then we see how scientists documented the single-quantum sensitivity of the eye seven decades earlier than ``ought'' to have been possible, and finally close with the remarkable signaling cascade that delivers such outstanding performance. Parts of this story are now embodied in a new textbook (WH Freeman and Co, 1/2015); additional course materials are available upon request. [Preview Abstract] |
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P1.00094: A new course and textbook on Physical Models of Living Systems, for science and engineering undergraduates Philip Nelson I'll describe an intermediate-level course on ``Physical Models of Living Systems.'' The only prerequisite is first-year university physics and calculus. The course is a response to rapidly growing interest among undergraduates in a broad range of science and engineering majors. Students acquire several research skills that are often not addressed in traditional courses: \begin{itemize}\itemsep1pt \parskip0pt \parsep0pt \item Basic modeling skills \item Probabilistic modeling skills \item Data analysis methods \item Computer programming using a general-purpose platform like MATLAB or Python \item Dynamical systems, particularly feedback control. \end{itemize} These basic skills, which are relevant to nearly any field of science or engineering, are presented in the context of case studies from living systems, including: \begin{itemize}\itemsep1pt \parskip0pt \parsep0pt \item Virus dynamics \item Bacterial genetics and evolution of drug resistance \item Statistical inference \item Superresolution microscopy \item Synthetic biology \item Naturally evolved cellular circuits. \end{itemize} [Preview Abstract] |
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P1.00095: Analytical framework for modeling of long-range transport of fungal plant epidemics Oleg Kogan, Kevin O'Keeffe, David Schneider, Christopher Myers A new framework for the study of long-range transport of fungal plant epidemics is proposed. The null nonlinear model includes advective transport through the free atmosphere, spore production on the ground, and transfer of spores between the ground and the advective atmospheric layer. The competition between the growth wave on the ground and the effect of the wind is most strongly reflected in upwind fronts, which can propagate into the wind for exponential initial conditions. If the rate of spore transfer into the advective layer is below critical, this happens for initital conditions with arbitrary steepness. Upwind fronts from localized initial conditions will propagate in the direction of the wind above this critical parameter, and will not propagate below it. On the other hand, the speed of the downwind front does not have a strong dependence on the rate of spore transfer between the advective layer and the ground. Thus, even vanishingly small, but finite transfer rates result in a substantial epidemic wave in the direction of the wind. We also consider the effect of an additional, random-walk like mechanism of transport through the near-ground atmospheric boundary layer, and attempt to understand which route dominates the transport over long distances. [Preview Abstract] |
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P1.00096: Interstitial flows promote an amoeboid cell phenotype and motility of breast cancer cells Chih-kuan Tung, Yu Ling Huang, Angela Zheng, Mingming Wu Lymph nodes, the drainage systems for interstitial flows, are clinically known to be the first metastatic sites of many cancer types including breast and prostate cancers. Here, we demonstrate that breast cancer cell morphology and motility is modulated by interstitial flows in a cell-ECM adhesion dependent manner. The average aspect ratios of the cells are significantly lower (or are more amoeboid like) in the presence of the flow in comparison to the case when the flow is absent. The addition of exogenous adhesion molecules within the extracellular matrix (type I collagen) enhances the overall aspect ratio (or are more mesenchymal like) of the cell population. Using measured cell trajectories, we find that the persistence of the amoeboid cells (aspect ratio less than 2.0) is shorter than that of mesenchymal cells. However, the maximum speed of the amoeboid cells is larger than that of mesenchymal cells. Together these findings provide the novel insight that interstitial flows promote amoeboid cell morphology and motility and highlight the plasticity of tumor cell motility in response to its biophysical environment. [Preview Abstract] |
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P1.00097: Robust Nonlinear Neural Codes Qianli Yang, Xaq Pitkow Most interesting natural sensory stimuli are encoded in the brain in a form that can only be decoded nonlinearly. But despite being a core function of the brain, nonlinear population codes are rarely studied and poorly understood. Interestingly, the few existing models of nonlinear codes are inconsistent with known architectural features of the brain. In particular, these codes have information content that scales with the size of the cortical population, even if that violates the data processing inequality by exceeding the amount of information entering the sensory system. Here we provide a valid theory of nonlinear population codes by generalizing recent work on information-limiting correlations in linear population codes. Although these generalized, nonlinear information-limiting correlations bound the performance of any decoder, they also make decoding more robust to suboptimal computation, allowing many suboptimal decoders to achieve nearly the same efficiency as an optimal decoder. Although these correlations are extremely difficult to measure directly, particularly for nonlinear codes, we provide a simple, practical test by which one can use choice-related activity in small populations of neurons to determine whether decoding is suboptimal or optimal and limited by correlated noise. We conclude by describing an example computation in the vestibular system where this theory applies. [Preview Abstract] |
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P1.00098: Spatiotemporal discrimination in neural networks with short-term synaptic plasticity Benjamin Shlaer, Paul Miller Cells in recurrently connected neural networks exhibit bistability, which allows for stimulus information to persist in a circuit even after stimulus offset, i.e. short-term memory. However, such a system does not have enough hysteresis to encode temporal information about the stimuli. The biophysically described phenomenon of synaptic depression decreases synaptic transmission strengths due to increased presynaptic activity. This short-term reduction in synaptic strengths can destabilize attractor states in excitatory recurrent neural networks, causing the network to move along stimulus dependent dynamical trajectories. Such a network can successfully separate amplitudes and durations of stimuli from the number of successive stimuli\footnote{Miller, P. (2013). Stimulus number, duration and intensity encoding in randomly connected attractor networks with synaptic depression. {\em Front.~Comput.~Neurosci.~} 7:59.}, and so provides a strong candidate network for the encoding of spatiotemporal information. Here we explicitly demonstrate the capability of a recurrent neural network with short-term synaptic depression to discriminate between the temporal sequences in which spatial stimuli are presented. [Preview Abstract] |
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P1.00099: The Brain Physics: Multi Laser Beam Interaction with the Brain Topions (the Brain Neurocenters) V. Alexander Stefan A novel method for the treatment of the neurological diseases is proposed. The multiple-energy laser photons\footnote{V. Alexander Stefan, NEUROPHYSICS, STEM CELL PHYSICS, and GENOMIC PHYSICS: Beat-Wave-Driven-Free Electron Laser Beam Interactions with the Living Matter (S-U-Press, La Jolla, CA, 2012)} (the blue scanning photons and ultraviolet focusing photons) interact with the specific DNA molecules within the topion (such as Parkinson's and Alzheimer's brain topion) via the matching of laser frequency with the oscillation eigen-frequency of a particular molecule\footnote{ V. Stefan, B. I. Cohen, C. Joshi, \textit{Science}, 243, 4890, (Jan.27, 1989); Stefan et al., Bull. APS 32, No.9, 1713, (1987); Stefan APS-March-2012, {\#} K1.00177.} within the DNA.\footnote{ V. Alexander Stefan, APS-March-2013, {\#}.H1.00208; APS-March-2014, {\#}. P1.00063.} In this way, the corrupt molecules (the structure of molecules) can be manipulated so as to treat (eliminate) the neurological disease. [Preview Abstract] |
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P1.00100: Network oscillations of inferior olive neurons: entrainment and phase-locking of locally-coupled oscillators Thomas Chartrand, Mark S. Goldman, Timothy J. Lewis Although the inferior olive is known to contribute to the generation of timing and error signals for motor control, the specific role of its distinctive spatiotemporal activity patterns is still controversial. Olivary neurons display regular, sometimes synchronized oscillations of subthreshold membrane potential, driven in part by the highest density of electrical coupling of any brain region. We show that a reduced model of coupled phase oscillators is sufficient to reproduce and study experimental observations previously only demonstrated in more complex models. These include stable phase differences, variability of entrainment frequency, wave propagation, and cluster formation. Using the phase-response curve (PRC) of a conductance-based model of olivary neurons, we derive our phase model according to the theory of weakly-coupled oscillators. We retain the heterogeneity of intrinsic frequencies and heterogeneous, spatially constrained coupling as weak perturbations to the limit-cycle dynamics. Generalizing this model to an ensemble of coupled oscillator lattices with frequency and coupling disorder, we study the onset of entrainment and phase-locking as coupling is strengthened, including the scaling of cluster sizes with coupling strength near each phase transition. [Preview Abstract] |
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P1.00101: Temporal Evolution Of Information In Neural Networks With Feedback Aram Giahi Saravani, Xaq Pitkow Recurrent neural networks are pivotal for information processing in the brain. Here we analyze how the information content of a neural population is altered by dynamic feedback of a stimulus estimated from the network activity. We find that the temporal evolution of the Fisher information in the model with feedback is bounded by the Fisher information in a network of pure integrators. The available information in the feedback model saturates with a time constant and to a final level both determined by the match between the estimator weights and the feedback weights. This network then encodes signals specifically from either the beginning or the end of the stimulus presentation, depending on this match. These results are relevant to recent experimental measurements of psychophysical kernels indicating that earlier stimuli have a stronger influence on perceptual discriminations than more recent stimuli. We discuss consequences of this description for choice correlations, a measure of how individual neuronal responses relate to perceptual estimates. [Preview Abstract] |
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P1.00102: ABSTRACT WITHDRAWN |
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P1.00103: The Deterministic Information Bottleneck D.J. Strouse, David Schwab A fundamental and ubiquitous task that all organisms face is prediction of the future based on past sensory experience. Since an individual's memory resources are limited and costly, however, there is a tradeoff between memory cost and predictive payoff. The information bottleneck (IB) method (Tishby, Pereira, \& Bialek 2000) formulates this tradeoff as a mathematical optimization problem using an information theoretic cost function. IB encourages storing as few bits of past sensory input as possible while selectively preserving the bits that are most predictive of the future. Here we introduce an alternative formulation of the IB method, which we call the deterministic information bottleneck (DIB). First, we argue for an alternative cost function, which better represents the biologically-motivated goal of minimizing required memory resources. Then, we show that this seemingly minor change has the dramatic effect of converting the optimal memory encoder from stochastic to deterministic. Next, we propose an iterative algorithm for solving the DIB problem. Additionally, we compare the IB and DIB methods on a variety of synthetic datasets, and examine the performance of retinal ganglion cell populations relative to the optimal encoding strategy for each problem. [Preview Abstract] |
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P1.00104: Modeling the Kinetics of a Memory-Associated Immediate Early Gene's Compartmental Expression After Sensory Experience Adam Willats, Tamara Ivanova, Astrid Prinz, Robert Liu Immediate Early Genes (IEGs) are rapidly and transiently transcribed in neurons after a sensory experience. Some of these genes act as effector IEGs, which mediate specific effects on cellular function. Arc is one such effector IEG that is essential for synaptic plasticity and memory consolidation in hippocampus and cortex. The expression of Arc in neurons has previously been examined using an imaging method known as Compartmental Analysis of Temporal Fluorescent In-Situ Hybridization. Previous work found that the time course of Arc expression within the nuclear and perinuclear cytoplasmic compartments of a neuron is altered by prior sensory experience. We explore a simple model of the kinetics of IEG transcription and nuclear export, with the aim of eventually uncovering possible mechanisms for how experience alters expression kinetics. Thus far, we characterize our compartmental model using phase-plane analysis and validate it against several IEG expression data sets, including one where prior experience with vocalizing mice alters the time course of call-induced Arc expression in the auditory cortex of a listening mouse. Our model provides a framework to explore why Arc expression may change depending on a receiver's past sound experience and internal state. [Preview Abstract] |
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P1.00105: The brain as a complex system: plasticity at multiple scales and criticality Tony Ng, Paul Miller As a complex system, a successful organism is one that can react effectively to environmental fluctuations. Not only should its response repertoire be commensurate with the number of independent conditions that it encounters, behavioral and environmental variations need to be matched at the appropriate scales. In the cortex, neuronal clusters, not individual cells, operate at the proper scale that is necessary to generate appropriate responses to external states of the world. Single neurons, however, serve on a finer scale to mediate interactions between neuronal assemblies. The distinction of scales is significant, as plasticity mechanisms can operate on various spatial and temporal scales. The brain has apparently evolved complex-system strategies to calibrate its own dynamics at multiple scales. This makes the joint study of local balance and global homeostasis fundamentally important, where criticality emerges as a signature of a computationally powerful system. We show via simulations how plasticity mechanisms at multiple scales are inextricably tied to spike-based neuronal avalanches, which are microscopic in origin and poorly predictive of animal behavior, and cluster-based avalanches, which are manifest macroscopically and are relevant to cognition and behavior. [Preview Abstract] |
(Author Not Attending)
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P1.00106: Marginalization in Random Nonlinear Neural Networks Rajkumar Vasudeva Raju, Xaq Pitkow Computations involved in tasks like causal reasoning in the brain require a type of probabilistic inference known as marginalization. Marginalization corresponds to averaging over irrelevant variables to obtain the probability of the variables of interest. This is a fundamental operation that arises whenever input stimuli depend on several variables, but only some are task-relevant. Animals often exhibit behavior consistent with marginalizing over some variables, but the neural substrate of this computation is unknown. It has been previously shown (Beck et al. 2011) that marginalization can be performed optimally by a deterministic nonlinear network that implements a quadratic interaction of neural activity with divisive normalization. We show that a simpler network can perform essentially the same computation. These Random Nonlinear Networks (RNN) are feedforward networks with one hidden layer, sigmoidal activation functions, and normally-distributed weights connecting the input and hidden layers. We train the output weights connecting the hidden units to an output population, such that the output model accurately represents a desired marginal probability distribution without significant information loss compared to optimal marginalization. Simulations for the case of linear coordinate transformations show that the RNN model has good marginalization performance, except for highly uncertain inputs that have low amplitude population responses. Behavioral experiments, based on these results, could then be used to identify if this model does indeed explain how the brain performs marginalization. [Preview Abstract] |
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P1.00107: Investigating structural details of lipid-cholesterol-A$\beta $ interactions Durgesh Rai, Divina Anunciado, William Heller, Hugh O'Neill, Volker Urban, Shuo Qian Alzheimer's disease (AD) is the most common form of dementia and is predicted to affect 1 in 85 people around the world by 2050. Amyloid beta (A$\beta )$-peptide, a peptide composed of 40- 42 amino acids that is the product of cleavage from the amyloid precursor protein (APP), is regarded to play a major role in the development of AD. In addition, accumulating evidence points to a positive association between cholesterol and AD. Here, we present results from our studies about A$\beta $-peptide and cholesterol in bilayer by small-angle neutron scattering (SANS) using a combination of dimyristoyl, phosphocholine (DMPC) and partially deuterated cholesterol (cholesterol-d7) with and without A$\beta $. We compare the results using grazing incidence and transmission SANS on lipid bilayer films and unilamellar vesicles respectively. The structural details on vesicles and bilayers work in conjunction with the circular dichroism on peptide in solution and oriented circular dichroism in bilayer films. The studies confirm a positive association of A$\beta $ with the membrane layers. The results from different studies will be compared and contrasted in presentation. [Preview Abstract] |
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P1.00108: Using Small Angle Neutron Scattering on Glucose Oxidase immobilized on Single Layer Graphene Durgesh Rai, M. Gurusaran, S. Qian, K. Weiss, V. Urban, P. Li, L. Ma, P. Ajayan, T. Narayanan, K. Sekar, S. Viswanathan, V. Renugopalakrishanan Reliable blood glucose monitoring using biosensors is valuable for health evaluations and medication in wake of chronic diabetic issues accompanying deviations from evolutionary human lifestyle. Glucose oxidase (GOx) is an ideal enzyme because of its specificity and the ability to electrochemically transduce from the enzymatic reaction. We use graphene-based electrode with GOx sensor matrix so that the emitted electrons from sensor matrix can flow across graphene nearly without scattering; crucial for constructing ultrasensitive-sensors. Thereafter, establishing a structure-property based relationships to tune the sensor topology with electrochemically output forms the main focus of the device development process. We have developed a methodology to obtain low-resolution hierarchical models of the aggregate matrix using Small Angle Neutron Scattering (SANS) technique. A Unified Fit model is used in tandem with GNOM, DAMMIN and DAMAVER to construct low-resolution models for GOx matrices. A detailed explanation of a general methodology for obtaining quantitative details aggregate structures along with qualitative models will be presented. [Preview Abstract] |
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P1.00109: Interatomic Coulombic Decay Effects in Theoretical DNA Recombination Systems Involving Protein Interaction Sites E.L. Vargas, D.A. Rivas, A.C. Duot, R.T. Hovey, V.M. Andrianarijaona DNA replication is the basis for all biological reproduction. A strand of DNA will ``unzip'' and bind with a complimentary strand, creating two identical strands. In this study, we are considering how this process is affected by Interatomic Coulombic Decay (ICD), specifically how ICD affects the individual coding proteins' ability to hold together. ICD mainly deals with how the electron returns to its original state after excitation and how this affects its immediate atomic environment, sometimes affecting the connectivity between interaction sites on proteins involved in the DNA coding process. Biological heredity is fundamentally controlled by DNA and its replication therefore it affects every living thing. The small nature of the proteins (within the range of nanometers) makes it a good candidate for research of this scale. Understanding how ICD affects DNA molecules can give us invaluable insight into the human genetic code and the processes behind cell mutations that can lead to cancer. [Preview Abstract] |
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P1.00110: Gramicidin Induce Local Non-Uniform Distribution of Lipids in Multi-Component Membrane Domains Yu Mao, Fazle Hussain, Juyang Huang In lipid membranes, gramicidin form trans-membrane channels that are specific for monovalent cations. We performed Molecular Dynamics simulations of gramicidin in coexisting liquid-ordered (Lo) and liquid disordered (Ld) domains using GROMACS. The lipid compositions of Lo and Ld domains are DOPC/DSPC/Cholesterol $=$ 6.5/52.6/40.9 and 74.4/10.6/15, respectively. In the Ld domain, the membrane thickness matches the hydrophobic length of gramicidin quite well, and water molecules can diffuse through the gramicidin channels. However, in the Lo lipid domain, the bilayer thickness is far greater than the hydrophobic length of gramicidin and majority of gramicidin do not form conducting channel. The simulation result explained our experimental finding that gramicidin partition favorably into the Ld domains. The calculated radial distribution functions of lipids indicate that gramicidin recruit a layer of short DOPC surrounding each protein and keep cholesterol and taller DSPC away from the protein-bilayer interface. Our result indicates that membrane proteins are capable of inducing non-uniform distributions of lipids and creating a local bilayer environment, which favors protein function. [Preview Abstract] |
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P1.00111: Directly mapping the surface charge density of lipid bilayers under physiological conditions Thomas Fuhs, Lasse Hyldgaard Klausen, Flemming Besenbacher, Mingdong Dong The surface charge density of lipid bilayers governs the cellular uptake of charged particles and guides cell-cell and cell-surface interactions. Direct probing of the potential requires sub nanometer distances as the electrostatic potential is screened by high physiological salt concentrations. This prevented direct measurement of the SCD under physiological conditions. In this study we investigate supported bilayers of lipid mixtures that form domains of distinct surface charges, submerged in 150mM NaCl. We use a scanning ion-conductance microscope (SICM) setup to measure the ionic current through a nanopipette as the pipette is scanned several nanometers above the sample. The charged headgroups of the lipids attract counter ions leading to a charge dependent enhancement of the ion concentration near the surface. This creates a measurable change of conductivity in the vicinity of the surface. As the dependency of the current on the SCD and pipette potential is non-trivial we characterized it using numerical solutions to Poisson and Nernst-Planck equations. Based on the simulation results we propose an imaging method. We confirm feasibility of the proposed method by experimentally mapping the local surface charge density of phase separated lipid bilayers. [Preview Abstract] |
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P1.00112: Lipid mobility in supported lipid bilayers by single molecule tracking Maryam Kohram, Xiaojun Shi, Adam Smith Phospholipid bilayers are the main component of cell membranes and their interaction with biomolecules in their immediate environment is critical for cellular functions. These interactions include the binding of polycationic polymers to lipid bilayers which affects many cell membrane events. As an alternative method of studying live cell membranes, we assemble a supported lipid bilayer and investigate its binding with polycationic polymers in vitro by fluorescently labeling the molecules of the supported lipid bilayer and tracking their mobility. In this work, we use single molecule tracking total internal reflection fluorescence microscopy (TIRF) to study phosphatidylinositol phosphate (PIP) lipids with and without an adsorbed polycationic polymer, quaternized polyvinylpyridine (QPVP). Individual molecular trajectories are obtained from the experiment, and a Brownian diffusion model is used to determine diffusion coefficients through mean square displacements. Our results indicate a smaller diffusion coefficient for the supported lipid bilayers in the presence of QPVP in comparison to its absence, revealing that their binding causes a decrease in lateral mobility. [Preview Abstract] |
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P1.00113: Nanoparticle size and shape characterization with Solid State Nanopores Santoshi Nandivada, Mourad Benamara, Jiali Li Solid State Nanopores are widely used in a variety of single molecule studies including DNA and biomolecule detection based on the principle of Resistive Pulse technique. This technique is based on electrophoretically driving charged particles through 35-60 nm solid state nanopores. The translocation of these particles produces current blockage events that provide an insight to the properties of the translocation particles and the nanopore. In this work we study the current blockage events produced by $\sim$ 30nm negatively charged PS nanoparticles through Silicon Nitride solid state nanopores. We show how the current blockage amplitudes and durations are related to the ratio of the volume of the particle to the volume of the pore, the shape of the particle, charge of the particle and the nanopore surface, salt concentration, solution pH, and applied voltage. The solid-state nanopores are fabricated by a combination of Focus Ion Beam and low energy Ion beams in silicon nitride membranes. High resolution TEM is used to measure the 3D geometry of the nanopores and a finite element analysis program (COMSOL) is used to simulate the experimental results. [Preview Abstract] |
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P1.00114: ABSTRACT WITHDRAWN |
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P1.00115: Characterizing detergent mediated reconstitution of viral protein M2 in large unilamellar vesicles Mariel Freyre, Carl Grossman, Catherine Crouch, Kathleen Howard Influenza M2 is a model membrane protein whose function is to induce curvature and vesicle formation in the process of viral infection. To study embedded M2 in synthetic phospholipid vesicles (large unilamellar vesicles or LUVs), a concentration of detergent and buffer is optimized to balance protein solubility, proteolipid concentration, and LUV stability. Adding detergent also causes the LUVs to partially disassemble and form micelles, which warrants detergent removal to restore LUV integrity. We explore methods of measuring the coexistence of detergent micelles and LUVs to track the different phases of the system as detergent is removed. A combination of Fluorescence Correlation Spectroscopy, Dynamic Light Scattering, and chemical analysis are used to measure the properties of this system. With detergent/LUV number densities as high as 5 we find coexistence of micelles and LUVs at 50\% to 60\%. As the detergent is removed, the micelle concentration drops to lower than 30\% while detergent levels drop to nearly zero. These results may indicate a polydispersed LUV size distribution after detergent mediated reconstitution. [Preview Abstract] |
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P1.00116: Preventing drug resistance in severe influenza Hana Dobrovolny, Lucas Deecke Severe, long-lasting influenza infections are often caused by new strains of influenza. The long duration of these infections leads to an increased opportunity for the emergence of drug resistant mutants. This is particularly problematic for new strains of influenza since there is often no vaccine, so drug treatment is the first line of defense. One strategy for trying to minimize drug resistance is to apply periodic treatment. During treatment the wild-type virus decreases, but resistant virus might increase; when there is no treatment, wild-type virus will hopefully out-compete the resistant virus, driving down the number of resistant virus. We combine a mathematical model of severe influenza with a model of drug resistance to study emergence of drug resistance during a long-lasting infection. We apply periodic treatment with two types of antivirals: neuraminidase inhibitors, which block release of virions; and adamantanes, which block replication of virions. We compare the efficacy of the two drugs in reducing emergence of drug resistant mutants and examine the effect of treatment frequency on the emergence of drug resistant mutants. [Preview Abstract] |
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P1.00117: Simultaneous influenza and respiratory syncytial virus infection in human respiratory tract Lubna Jahan Rashid Pinky, Hana Dobrovolny Studies have shown that simultaneous infection of the respiratory tract with at least two viruses is not uncommon in hospitalized patients, although it is not clear whether these infections are more or less severe than single infections. We use mathematical models to study the dynamics of simultaneous influenza (flu) and respiratory syncytial virus (RSV) infection, two of the more common respiratory viruses, in an effort to understand simultaneous infections. We examine the roles of initial viral inoculum, relative starting time, and cell regeneration on the severity of the infection. We also study the effect of antiviral treatment on the course of the infection. This study shows that, unless treated with antivirals, flu always takes over the infection no matter how small the initial dose and how delayed it starts with respect to RSV. [Preview Abstract] |
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P1.00118: Determining Mechanism of Action of Antivirals for Respiratory Illness Irma Rodriguez, Hana Dobrovolny Viral infections in the respiratory tract are common in humans and can cause serious illness and death. Drug treatment is the principal line of protection against many of these illnesses and many compounds are tested as antivirals. Often the efficacy of these antivirals are determined before a mechanism of action is understood. We use mathematical models to represent the evolution of these diseases and establish which experiments can help determine the mechanism of action of antivirals. [Preview Abstract] |
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P1.00119: Object-adapted trapping and shape-tracking to probe a bacterial protein chain motor Julian Roth, Matthias Koch, Alexander Rohrbach The helical bacterium Spiroplasma is a motile plant and anthropod pathogen which swims by propagating pairs of kinks along its cell body. As a well suited model system for bacterial locomotion, understanding the cell's molecular motor is of vital interest also regarding the combat of bacterial diseases. The extensive deformations related to these kinks are caused by a contractile cytoskeletal protein ribbon representing a linear motor in contrast to common rotary motors as, e.g., flagella. We present new insights into the working of this motor through experiments with object-adapted optical traps and shape-tracking techniques. We use the given laser irradiation from the optical trap to hinder bacterial energy (ATP) production through the production of O$_{2}$ radicals. The results are compared with experiments performed under the influence of an O$_{2}$-Scavenger and ATP inhibitors, respectively. Our results show clear dependences of the kinking properties on the ATP concentration inside the bacterium. The experiments are supported by a theoretical model which we developed to describe the switching of the ribbon's protein subunits. [Preview Abstract] |
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P1.00120: Modeling the Lymphocytic Choriomeningitis Virus: Insights into understanding its epidemiology in the wild Christy Contreras, John McKay, Joseph Blattman, Susan Holechek The lymphocytic choriomenigitis virus (LCMV) is a rodent-spread virus commonly recognized as causing neurological disease that exhibits asymptomatic pathology. The virus is a pathogen normally carried among rodents that can be transmitted to humans by direct or indirect contact with the virus in excretions and secretions from rodents and can cause aseptic meningitis and other conditions in humans. We consider an epidemiological system within rodent populations modeled by a system of ordinary differential equations that captures the dynamics of the diseases transmission and present our findings. The asymptotic nature of the pathogen plays a large role in its spread within a given population, which has motivated us to expand upon an existing SIRC model (Holechek et al in preparation) that accounts for susceptible-, infected-, recovered-, and carrier-mice on the basis of their gender. We are interested in observing and determining the conditions under which the carrier population will reach a disease free equilibrium, and we focus our investigation on the sensitivity of our model to gender, pregnancy related infection, and reproduction rate conditions. [Preview Abstract] |
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P1.00121: ABSTRACT WITHDRAWN |
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P1.00122: Feeding strategies as revealed by the section moduli of the humerus bones in bipedal theropod dinosaurs Scott Lee, Zachary Richards The section modulus of a bone is a measure of its ability to resist bending torques. Carnivorous dinosaurs presumably had strong arm bones to hold struggling prey during hunting. Some theropods are believed to have become herbivorous and such animals would not have needed such strong arms. In this work, the section moduli of the humerus bones of bipedal theropod dinosaurs (from \textit{Microvenator celer} to \textit{Tyrannosaurus rex}) are studied to determine the maximum bending loads their arms could withstand. The results show that bending strength is not of uniform importance to these magnificent animals. The predatory theropods had strong arms for use in hunting. In contrast, the herbivorous dinosaurs had weaker arms. [Preview Abstract] |
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P1.00123: Microrheology of single microtubule filaments and synthesized cytoskeletal networks Matthias Koch, Alexander Rohrbach The ability to sense and respond to external mechanical forces is crucial for cells in many processes such as cell growth and division. Common models on mechanotransduction rely on the conversion of mechanical stimuli to chemical signals in the cell periphery and their translocation by diffusion (passive) or molecular motors (active). These processes are rather slow ($\sim$ seconds) and it has been argued that the cytoskeleton itself might be able to transport a mechanical signal within microseconds via stress waves. Microtubules are the stiffest component of the cytoskeleton and thus ideal candidates for this purpose. We study the frequency dependent response of single microtubule filaments and small networks thereof in a bottom-up approach using several (N$=$2-10) time-multiplexed optical tweezers together with back focal plane interferometry. Small synthesized networks with a defined geometry are constructed using trapped Neutravidin beads as anchor points for biotinylated filaments. The network is then probed by a defined oscillation of one anchor (actor). The frequency dependent response of the remaining beads (sensors) is analyzed experimentally and modeled theoretically over a wide frequency range. [Preview Abstract] |
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P1.00124: Biviscous blood flow and a new method for velocity profile adjustment Carlos Velazquez, Adrian Reyes In this paper we describe our proposal of a new numerical procedure for the adjusting of the velocity profile of body fluids with two viscosities. We have focused on the relevant case of the human blood and we have selected a particular model, the biviscous blood model, with the purpose of proving the convenience of our method. We start by describing the convenience of the biviscous stress equation as a model for the blood constitutive equation, then we solve it in the particular case of a stationary flow and use this solutions as the basis of our numerical procedure, which is described afterwards. Then, we present its implementation for analyzing in vivo measurements and exhibit its pertinence. Finally, we explain the design of a programmatic code of an automatic routine which is capable of applying our method and therefore could be used as the basis of an automatic implementation in new diagnosis software within a measurement device. [Preview Abstract] |
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P1.00125: Femoral bone strength in large theropod dinosaurs: A study by genus Scott Lee The locomotion of bipedal theropod dinosaurs is controlled by the strength of the femur to resist bending torques (caused by the foot striking the ground and the action of muscles on the femur). The section modulus at the narrowest part measures the ability of the femur to resist such torques. We present the results of our study of the femoral section moduli for six genus of large theropods: \textit{Tyrannosaurus}, Nanotyrannus, Gorgosaurus, and \textit{Albertosaurus} of the Late Cretaceous, \textit{Acrocanthosaurus} of the Early Cretaceous, and \textit{Allosaurus} of the Late Jurassic. These animals had femora of lengths between 65 and 134 cm. The corresponding section moduli varied between 23 and 570 cm$^{3}$. Some species of \textit{Tyrannosaurus, Gorgosaurus, Allosaurus}, and \textit{Albertosaurus} had femora with lengths in the same 75 to 90 cm range. The section moduli of these animals are all in the same range, showing that the animals had the same abilities of locomotion. That is, \textit{Allosaurus} of the Late Jurassic could locomote just as well as the Late Cretaceous \textit{Tyrannosaurus}, Gorgosaurus, and \textit{Albertosaurus}. There is no evidence that these later theropods had evolved to be any faster than similarly-sized theropods living about 80 million years earlier. [Preview Abstract] |
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P1.00126: Allometry in dinosaurs and mammals Scott Lee The proportions of the leg bones change as the size of an animal becomes larger since the mass of the animal increases at a faster rate than the cross-sectional area of its leg bones. For the case of elastic similarity (in which the longitudinal stress in the legs remains constant in animals of all sizes), the diameter d and length L of the femur should be related as d = A L$^{3/2}$. For geometric similarity (in which all dimensions are scaled by the same factor), d = A L. For animals with femora longer than 20 cm, we find the power law relationship to be d = A L$^{b}$ with b = 1.13 $\pm$ 0.06 for extant mammals (the largest mammal being \emph{Loxodonta africana} with a 1.00-m-long femur) and b = 1.18 $\pm$ 0.02 for dinosaurs (the largest dinosaur being \emph{Brachiosaurus brancai} with a 2.03-m-long femur). These data show that extinct dinosaurs and extant animals scale in the same basic manner. The large sauropods (with femora twice as long as found in elephants) scale in a manner consistent with extrapolation of the scaling shown by extant mammals. These results argue that extinct dinosaurs moved in a manner very similar to extant mammals. [Preview Abstract] |
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P1.00127: Direct Osmolyte-Macromolecule Interactions Confer Entropic Stability to Folded States Francisco Rodriguez-Ropero, Nico F.A. van der Vegt Protective osmolytes are chemical compounds that shift the (bio)macromolecule folding/unfolding equilibrium toward the folded state under osmotic stresses. Traditionally it has been considered that omolytes are depleted from the macromolecule first solvation shell, leading to entropic stabilization of the folded state. Recent theoretical and experimental studies suggest that protective osmolytes may directly interact with the macromolecule. As an exemplary and experimentally well-characterized system, we herein discuss poly(N-isopropylacrylamide) (PNiPAM) in water whose folding/unfolding equilibrium shifts toward the folded state in the presence of urea. Based on Molecular Dynamics simulations we show that urea preferentially accumulates in the first solvation shell of PNiPAM driven by attractive van der Waals dispersion forces leading to the formation of urea clouds around the polymer. Solvation thermodynamics analysis of the folded and unfolded states discards direct urea/macromolecule interactions as driving force of the folding mechanism. Our data shows that entropic penalization of unfolded polymer chains upon increasing urea concentration drives the collapse of the polymer chain. [Preview Abstract] |
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P1.00128: Quantifying macromolecular conformational transition pathways Sean Seyler, Avishek Kumar, Michael Thorpe, Oliver Beckstein Diverse classes of proteins function through large-scale conformational changes that are challenging for computer simulations. A range of fast path-sampling techniques have been used to generate transitions, but it has been difficult to compare paths from (and assess the relative strengths of) different methods. We introduce a comprehensive method (pathway similarity analysis, PSA) for quantitatively characterizing and comparing macromolecular pathways. The Hausdorff and Fr\'{e}chet metrics (known from computational geometry) are used to quantify the degree of similarity between polygonal curves in configuration space. A strength of PSA is its use of the full information available from the 3$N$-dimensional configuration space trajectory without requiring additional specific knowledge about the system. We compare a sample of eleven different methods for the closed-to-open transitions of the apo enzyme adenylate kinase (AdK) and also apply PSA to an ensemble of 400 AdK trajectories produced by dynamic importance sampling MD and the Geometrical Pathways algorithm. We discuss the method's potential to enhance our understanding of transition path sampling methods, validate them, and help guide future research toward deeper physical insights into conformational transitions. [Preview Abstract] |
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P1.00129: Interaction of Human Serum Albumin with Metal Protoporphyrins Jie Hu, Lorenzo Brancaleon Fluorescence spectroscopy is widely used in biotechnology, nanotechnology, and molecular biophysics, since it can provide information on a wide range of molecular processes, e.g. the interactions of solvent molecules with fluorophores, conformational changes, and binding interactions etc. In this study, we present the photophysical properties of the interaction of human serum albumin (HSA) with a series of metal compound of Protoporphyrin IX (PPIX), including ZnPPIX, FePPIX, MgPPIX, MnPPIX and SnPPIX respectively, as well as the free base PPIX. Binding constants were retrieved independently using the Benesi-Hildebrand analysis of the porphyrin emission or absorption spectra and the fluorescence quenching (i.e. Stern-Volmer analysis) and reveal that the two methods yield a difference of approximately one order or magnitude between the two. Fluorescence lifetimes was used to probe whether binding of the porphyrin changes the conformation of the protein or if the interaction places the porphyrin at a location that can prompt resonance energy transfer with the lone Tryptophan residue. In recent years it has been discovered that HSA provides a specific binding site for metal-chelated protoporphyrins in subdomain IA. This has opened a novel field of study over the importance of this site for biomedical applications but it has also created the potential for a series of biotechnological applications of the HSA/protoporphyrin complexes. Our study provides a preliminary investigation of the interaction with metal-chelated protoporphyrins that had not been previously investigated. [Preview Abstract] |
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P1.00130: Replica-exchange Wang-Landau simulations of the H0P model of protein folding Guangjie Shi, David P. Landau, Thomas W\"{u}st, Ying Wai Li Li The hydrophobic-polar (HP) model has served as a coarse-grained lattice protein folding model attracting scientists from various disciplines. However, simplification into H and P monomers may yield high ground state degeneracies which stands in contrast to the generally unique native states of natural proteins. We propose a simple modification, by introducing a new type of ``neutral'' monomer, 0, i.e. neither hydrophobic nor polar, rendering the model more realistic without increasing the difficulties of sampling significantly. With the newly developed parallel Wang-Landau (replica exchange Wang-Landau) scheme\footnote{T. Vogel, Y. W. Li, T. W\"{u}st, and D. P. Landau, Phys. Rev. Lett., 110, 210603 (2013)} and an innovative method of estimating the ground state degeneracies,\footnote{G. Shi, T. Vogel, T. W\"ust, Y. W. Li, and D. P. Landau, Phys. Rev. E 90, 033307} we investigated some widely studied HP proteins and their H0P counterparts. Dramatic differences in ground state and thermodynamic properties have been observed, e.g. the estimation of ground state degeneracy for the 46mer is 460,000 for the HP version and only 20 for the H0P mapping. Similarly, the specific heat and structural properties: radius of gyration and etc. show more pronounced signals associated with folding. [Preview Abstract] |
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P1.00131: Ergodic protein dynamics underlie the universal shape of protein distribution in populations Naama Brenner, Erez Braun, James Rotella, Hanna Salman We have previously shown that protein fluctuations in cell populations exhibit a universal distribution shape under a broad range of biological realizations. Here we report new results based on continuous measurement in individual bacteria for over $\sim$ 70 generations, which show that single-cell protein trajectories sample the available states with the same distribution shape as the population, i.e. protein fluctuations are ergodic. Analysis of temporal trajectories reveals that one effective random variable, sampled once each cell cycle, suffices to reconstruct the distribution from the trajectory. This in turn implies that cellular microscopic processes are strongly buffered and population-level protein distributions are insensitive to details of the intracellular dynamics. Probing them thus requires searching for novel universality-breaking experimental perturbations. [Preview Abstract] |
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P1.00132: Two-Dimensional Graphene Optoelectronic Probes for DNA Detection Tu Hong, Rui Wang, Xuanyang Ge, Yaqiong Xu With high charge-carrier mobility and large surface-area-to-volume ratio, graphene has become one of the most promising materials for biological and biomedical applications. Here, we demonstrate that graphene field-effect transistors combined with scanning photocurrent microscopy are ideal platforms for detecting DNA molecules. When negatively-charged DNA molecules are attached to graphene surface, significant photocurrent signals can be detected due to the local conductivity change in graphene. Our experimental results show that DNA-induced photocurrent response of graphene can be modulated by adjusting the electrochemical potential through an electrolyte gate. This study indicates that two-dimensional graphene optoelectronic probes can be used to explore the local electrostatic environment change with high electrical sensitivity. [Preview Abstract] |
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P1.00133: FLUIDS |
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P1.00134: Effect of Confinement on the Bubble Points of Hydrocarbons in Controlled-Pore Glasses Sheng Luo, Jodie Lutkenhaus, Hadi Nasrabadi Phase behavior in shale remains a challenging problem in the petroleum industry due to many complexities. One complexity is the strong surface-fluid interactions in shale nano-scale pores. These interactions can lead to a heterogeneous distribution of molecules, which conventional bulk-phase thermodynamics fails to describe. Herein, we report a study on the bubble points of various hydrocarbons confined in nanoporous controlled-pore glasses of 4.3 to 38.1 nm pore diameter. Differential scanning calorimetry is used to measure the temperature at which the gas phase begins to form (i.e. bubble point). Besides pore diameter, the relative hydrocarbon loading in the controlled-pore glass is evaluated. The findings suggest that the bubble point is dramatically affected by pore diameter. [Preview Abstract] |
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P1.00135: Liquid Crystals under Photo-patterned Spatially Varying Boundary Conditions Miao Jiang, Yu-Bing Guo, Qi-Huo Wei Liquid crystals under geometric confinements are of not only fundamental interest but also practical importance to applications such as chemical sensing and smart windows. Orientations of liquid crystal molecules in most geometric confinements are uniform at the boundaries and not highly controllable. In this paper, we will present a novel photoalignment technique to pattern spatially varying complex orientation fields, and discuss experimental studies on nematic liquid crystals under confinements of two parallel plates with various well designed molecular orientation fields. [Preview Abstract] |
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P1.00136: Two-dimensional Yukawa fluids Minerva Gonzalez-Melchor, Arlette Mendez, Jose Alejandre When the movement of particles is performed predominantly in two dimensions, the systems can be considered at a good extent as two-dimensional. For instance the lipids in a bilayer, micrometric particles in a quasi-two-dimensional colloidal suspension, colloids in a monolayer deposited on the air-water interface, and DNA complexes trapped at the water surface can be described at a first approach as bidimensional fluids. These systems are important for many applications in surface and colloidal science. In simulations where the explicit interface between liquid and vapor is present, the line tension can be directly computed. In this work we present molecular dynamics results obtained for the liquid/vapor coexistence curve of 2D Yukawa fluids and for the line tension. A comparison with the three-dimensional case is also presented. [Preview Abstract] |
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P1.00137: Heat Transfer Enhancement in Forced Convective Boiling in Microchannels by Periodic Electrospun Nanofiber Coatings Alexander Yarin, Martin Freystein, Felix Kolberg, Sumit Sinha-Ray, Rakesh Sahu, Lucas Spiegel, Tatiana Gambaryan-Roisman, Peter Stephan To enhance heat transfer in forced convective boiling the microchannel bottom was amended by a nano-texture - periodic rectangular mats of electrospun polymer nanofibers. The fibers were $\sim$ 300-500 nm in diameter and the mat thicknesses were about 6-15 $\mu$m. The test fluid was FC-72 and the flow in microchannels contained trains of Taylor bubbles. The role of the nanofibers was to retain the warm microchannel bottom wet, to prevent dry-out and thus to enhance the heat removal rate. In the present experiments the time-average heat flux and heat transfer coefficient at the nanofiber-coated domains were found to be 1.5-2 times higher than those at the uncoated ones. Accordingly, a significant decrease (by 5-8 K) in the superheat was observed at the same \textit{Re} of 387 and power supply of 36.1 kW/m2. At a higher \textit{Re} of 432 and lower power supply of 28.1 kW/m2 similar trends in the heat removal rate and surface superheat were found. The significant enhancement of the heat transfer results from the fact that nanofiber mats facilitate wetting of surface under passing Taylor bubbles, thus delaying formation of vapor flow at the channel bottom. The interstices of the nanofiber mat act as the nucleation sites facilitating formation of tiny bubbles, which eventually results in a higher heat removal rate from the surface at a reduced superheat. [Preview Abstract] |
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P1.00138: A simulation study of flow dynamics of erythrocytes through diverging and converging bifurcations Tong Wang, Zhongwen Xing A numerical model has been developed to predict the cells deformation and motion in a symmetric diverging and converging bifurcation of a microchannel. Fluid dynamics and membrane mechanics are incorporated. The model was utilized to evaluate the effect of different biophysical parameters, such as: initial cell position, membrane stiffness and shape of the cells on deformation and motion of the erythrocytes in the bifurcating curved microchannel. The numerical results demonstrate that erythrocytes in microvessels blunt velocity profiles in both straight section and daughter branches, and the transit velocity of erythrocytes is strongly influenced by cell deformability, shape of the cells, and the vessel geometry. These results may provide fundamental knowledge for a better understanding of hemodynamic behavior of microscale blood flow. [Preview Abstract] |
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P1.00139: Fluid flow calculations of Graphene Composites Amirhessam Tahmassebi, Alper Buldum The flow of fluids through carbon nanotubes was investigated in order to get a better understanding of the unique properties and phenomena of nano-fluidics. The previous modeling and simulation efforts were based on diffusion of atoms or molecules that were thrown to the nanotubes with initial velocities. This talk has shed some light on the flow of fluids using molecular dynamic simulations of different types of carbon nanotubes that were embedded in liquid argon using a moving wall piston of graphene. We focused on analyzing pressure difference, velocities, and momentum conservation in different regions. [Preview Abstract] |
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P1.00140: The effects of surface roughness on the contact line friction coefficients of water droplets on micro$\backslash $nano-patterned surfaces Jiangtao Cheng We report the effects of surface roughness on contact line friction coefficient (CLFC) of water droplets on micro- and nano-patterned surfaces. Both advancing and receding CLFCs have been measured on smooth, one-tier (with micropillars), and two-tier (with CNTs grown on micropillars) surfaces. In comparison with smooth surface, superhydrophobic surfaces can decrease both the advancing and receding CLFCs by more than 10 times. However, droplets on one-tier surfaces exhibit different dynamic behaviors in advancing and receding movements. We investigated the Wenzel-Cassie state transition on micropillar structures and found that the receding motion of a droplet on micropillars is dominated by the Wenzel model with significant receding contact line pinning, which leads to higher receding CLFC. However, rolling mechanism of liquid particles near the advancing contact line controls the advancing motion of a droplet on micropillars. There is a high tendency for an advancing droplet to exhibit Cassie-type behavior on one-tier surfaces and hence advancing CLFC is considerably mitigated. On two-tier superhydrophobic surfaces, it is the Cassie--Baxter behavior that dominates both the advancing and receding contact line motions giving rise to less friction coefficients. [Preview Abstract] |
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P1.00141: Patterns, Instabilities, Colors, and Flows in Vertical Foam Films Subinuer Yilixiati, Ewelina Wojcik, Yiran Zhang, Collin Pearsall, Vivek Sharma Foams find use in many applications in daily life, industry and biology. Examples include beverages, firefighting foam, cosmetics, foams for oil recovery and foams formed by pollutants. Foams are collection of bubbles separated by thin liquid films that are stabilized against drainage by the presence of surfactant molecules. Drainage kinetics and stability of the foam are strongly influenced by surfactant type, addition of particles, proteins and polymers. In this study, we utilize the thin film interference colors as markers for identifying patterns, instabilities and flows within vertical foam films. We experimentally study the emergence of thickness fluctuations near the borders and within thinning films, and study how buoyancy, capillarity and gravity driven instabilities and flows, are affected by variation in bulk and interfacial physicochemical properties dependent on the choice of constituents. [Preview Abstract] |
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P1.00142: Diving dynamics of seabirds Sunghwan Jung, Brian Chang, Matt Croson, Lorian Straker, Carla Dove Diving is the activity of falling from air into water, which is somewhat dangerous due to the impact. Humans dive for entertainments less than 20 meters high, however seabirds dive as a hunting mechanism from more than 20 meters high. Moreover, most birds including seabirds have a slender and long neck compared to many other animals, which can potentially be the weakest part of the body upon axial impact compression. Motivated by the diving dynamics, we investigate the effect of surface and geometric configurations on structures consisting of a beak-like cone and a neck-like elastic beam. A transition from non-buckling to buckling is characterized and understood through physical experiments and an analytical model. [Preview Abstract] |
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P1.00143: POLYMER PHYSICS |
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P1.00144: Orthogonal gradient networks via post polymerization reaction Pandiyarajan Chinnayan Kannan, Jan Genzer We report a novel synthetic route to generate orthogonal gradient networks through post polymerization reaction using pentaflurophenylmethacrylate (PFPMAc) active ester chemistry. These chemoselective monomers were successfully copolymerized with 5 mole{\%} of the photo (methacryloyloxybenzophenone) and thermal (styrenesulfonylazide) crosslinkers. Subsequently, the copolymers were modified by a series of amines having various alkyl chain lengths. The conversion of post polymerization reaction was monitored using Fourier Transform Infrared Spectroscopy (FT-IR) and noticed that almost all pentaflurophenyl moieties are substituted by amines within in an hour without affecting the crosslinkers. In addition, the incorporation of photo and thermal crosslinkers in the polymer enabled us to achieve stable and covalently surface-bound polymer gradient networks (PGN) in an orthogonal manner, i.e. complete control over the crosslink density of the network in two opposite directions (i.e. heat vs photo). The network properties such as wettability, swelling and tensile modulus of the gradient coatings are studied and revealed in the paper. [Preview Abstract] |
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P1.00145: Enthalpy Relaxation of a DGEBA Epoxy as a function of Time, Temperature, and Cooling Rate Caitlyn M. Clarkson, John D. McCoy, Jamie M. Kropka Enthalpy relaxation resulting from physical aging of a DGEBA epoxy, Epon 828, cross-linked with an amine curative, Jeffamine T-403, was studied for two isothermal aging temperatures at sequential aging times up to two weeks. Results were analyzed using the peak shift method to obtain the relaxation parameters $\beta$, $\delta$ (H*), and $\chi$. The individual effects of cooling rate from the equilibrated state, aging time, and aging temperature were isolated to understand the initial state of the glassy epoxy and its evolution during physical aging. [Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.] [Preview Abstract] |
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P1.00146: Frank-Kasper and other superlattice formations in a set of giant molecules having ABn type of Janus particles Xueyan Feng, Yiwen Li, Mingjun Huang, Chi-Hao Hsu, Stephen Z.D. Cheng A novel serial of precisely defined giant molecules having ABn type of Janus particles has been designed and synthesized. They are consisted of one functionalized hydrophilic polyhedral oligomeric silsesquioxane (POSS) (A) connected with different number of hydrophobic POSS cages (B, n$=$2-6). With variation of the interaction functional groups on A and the number of the coordinated hydrophobic POSS B, different superlattice structures could be formed at a sub-10-nm scale. For example, the superlattice structure of DPOSS-BPOSS2 (DPOSS represents seven hydroxyl group functionalized POSS and BPOSS represents isobutyl POSS) could change from a double-dyroids phase to a hexagonally packed cylinder phase with increasing temperature, due to an order-order transition in the weak segregation region. For DPOSS-BPOSS3 and DPOSS-BPOSS4, both of these giant molecules could form A15 phase, which is a Frank-Kasper phase. With deep understanding of this set of model ABn type giant molecules based on the POSS nano atoms, it may be promising to construct new generations of giant molecules for further development of functional materials with desired structures and macroscopic properties. [Preview Abstract] |
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P1.00147: Strain Rate Dependence of Compressive Yield and Relaxation in DGEBA Epoxies Gabriel K. Arechederra, Riley C. Reprogle, Caitlyn M. Clarkson, John D. McCoy, Jamie M. Kropka, Kevin N. Long, Robert S. Chambers The mechanical response in uniaxial compression of two diglycidyl ether of bisphenol-A epoxies were studied. These were 828DEA (Epon 828 cured with diethanolamine (DEA)) and 828T403 (Epon 828 cured with Jeffamine T-403). Two types of uniaxial compression tests were performed: A) constant strain rate compression and B) constant strain rate compression followed by a constant strain relaxation. The peak (yield) stress was analyzed as a function of strain rate from Eyring theory for activation volume. Runs at different temperatures permitted the construction of a mastercurve, and the resulting shift factors resulted in an activation energy. Strain and hold tests were performed for a low strain rate where a peak stress was lacking and for a higher strain rate where the peak stress was apparent. Relaxation from strains at different places along the stress-strain curve was tracked and compared. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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P1.00148: Template-directed synthesis of structurally-defined branched polymer architectures Amanda Marciel In this work, we describe a hybrid synthetic strategy to produce structurally-defined branched polymer architectures based on chemically-modified DNA. Overall, this approach enables precise control over branch placement, grafting density, and chemical identity of side branches. We utilize a two-step scheme based on polymerase chain reaction (PCR) for site-specific incorporation of non-natural nucleotides, followed by copper-free click chemistry for grafting side branches at specific locations along the main polymer backbone. Linear DNA backbones are first synthesized via PCR utilizing the promiscuity of a high yield thermophilic DNA polymerase to incorporate nucleotides containing bioorthogonal dibenzocyclooctyne functional groups at precise locations along one strand of a double stranded DNA backbone. Following PCR, copper-free click chemistry is used to attach synthetic polymer branches or oligonucleotide branches to the DNA backbone, thereby allowing for the design and synthesis of a variety of precise polymer architectures, including three-arm stars, H-polymers, and graft block copolymers. [Preview Abstract] |
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P1.00149: Light scattering measurement of sodium polyacrylate products Nisha Lama, David Norwood, Steven Boone, Valerie Massie-Boyer In the presentation, we will describe the use of a multi-detector HPLC incorporating the DAWN EOS multi-angle laser light scattering (MALLS) detector to measure the properties such as molecular weight, RMS radius, contour and persistence length and polydispersity of sodium polyacrylate products. The samples of sodium polyacrylate are used in various industries as thickening agents, coating dispersants, artificial snow, laundry detergent and disposable diapers. Data and results obtained from the experiment will be presented. [Preview Abstract] |
(Author Not Attending)
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P1.00150: Kinetics of the coil-to-globule transition in aqueous solution of poly (N-isopropoylacrylamide) Reza Farasat In an aqueous solution, poly (N-isopropoylacrylamide) (PNIPAM) undergoes a reversible coil-to-globule phase transition that occurs above the lower critical solution temperature (LCST). The transition is driven by temperature-dependent molecular interactions that include hydrogen bonding and hydrophobic association. By increasing the temperature above LCST, the PNIPAM-water bonds break, and the polymer coils collapse to globules. The process is accompanied by an endothermic thermal effect which is detectable by Differential Scanning Calorimetry (DSC). A 10 wt. {\%} solution of PNIPAM in water was prepared and subjected to DSC experiments under different heating rates (from 0.5 to 16$^{\circ}$C min$^{-1})$. With increasing the heating rate, the transition temperature as well as the DSC peak shift to higher temperature. The DSC data have been analyzed by an isoconversional method to evaluate the temperature dependence of the effective activation energy of the process. The resulting dependencies have been interpreted in terms of a nucleation kinetics model. The process has also been studied under nanoconfinement by introducing the PNIPAM solution into the silica nanopores. The results obtained under nanoconfinement are compared to those obtained for the bulk solution. [Preview Abstract] |
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P1.00151: SEMI CRYSTALLINE POLYMERS |
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P1.00152: Effect of Crystallinity on Melt Memory of Random Ethylene Copolymers Xuejian Chen, Al Mamun, Alamo G. Rufina A strong melt memory effect of crystallization has been observed in random ethylene copolymers even above the equilibrium melting temperature. Melt memory is associated with seeds that increase the crystallization rate of copolymers in a range of comonomer content between 0.5 and 4.5 mol{\%}. The seeds are taken as molten ethylene sequences that remain in close proximity and are unable to diffuse fast to the randomized melt state. Fast diffusion is restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. The molten nature of the self-seeds is supported by a linear variation of T$_{2}^{\mathrm{H}}$ with T$_{\mathrm{melt}}$ n NMR experiments in a range from 180 $^{\circ}$C to 100 $^{\circ}$C, covering both the homogeneous and heterogeneous melt regions. The effect of topological constraints on melt memory, or on number of seeds that remain in the melt, was analyzed studying copolymers with different levels of crystallinity. There is a threshold level of crystallinity, which depends on type and concentration of comonomer, below which copolymers do not display strong melt memory. Increasing 1-hexene content from 0.5 to 3.5 mol{\%}, the crystallinity threshold decreases from 39 to 4{\%}, while decreasing branch length from hexyl to ethyl, the threshold crystallinity decreases from 18{\%} to 5{\%} in agreement with stronger melt memory in copolymers with increasing comonomer content and with shorter branches. [Preview Abstract] |
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P1.00153: Structural Analysis of Semiconducting Polymers Exposed to High Energy Radiation Saeed Ahmadi Vaselabadi, Nikhila Mahadevapuram, David Shakarisaz, Joseph Strzalka, Paul Ruchhoeft, Gila Stein Semicrystalline polymers are used in low-cost electronics such as solar cells, thin film transistors, and light-emitting diodes. Their optoelectronic performance in these devices is partly dictated by molecular ordering and nanoscale structure, where the latter is particularly difficult to control. We used atom-beam radiation to crosslink the polymer poly(3-hexylthiophene) into nanoscale and microscale patterns. Ionizing radiation sources generate intermolecular cross-links that render the polymer insoluble in organic solvents. Grazing-incidence Wide-angle X-ray Scattering (GIWAXS) was used to investigate the effects of irradiation on molecular ordering of poly(3-hexylthiophene). We found that crosslinking will disrupt intermolecular ordering (reduce crystallinity and crystalline grain sizes). We also found that X-ray exposure during the WAXS measurements can induce the crosslinking through a similar mechanism, and we propose a simple method to test for the damage caused by these measurements. As an example, we find that poly (3-hexylthiophene) has measurable cross-links after 20 sec exposure to 7.35 keV radiation with flux of $1 * 10^{11}$ photons/sec at an incident angle of 0.5$^{\circ}$ . [Preview Abstract] |
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P1.00154: Mechanical properties of syndiotactic polypropylene (sPP) gels: the effects of temperature and solute concentration Ryusuke Okoshi, Atsushi Hotta The effects of the solute concentration on the microstructures and the mechanical properties of quenched syndiotactic polypropylene (sPP) gels were investigated. Our group has previously reported a highly resilient sPP gel quenched using liquid nitrogen (Gel LN). In this research, sPP/decahydronaphtalene gels were prepared varying the sPP concentrations from 5 to 20 wt{\%}. Compression test was carried out to evaluate the mechanical properties. Scanning electron microscopy (SEM) was conducted to analyze the microstructures. Gel LN with the sPP concentration of 20 wt{\%} presented a high fracture stress of 2400 kPa. A high fracture strain of 70{\%} was also observed for all Gel LN samples. By contrast, sPP gels with the sPP concentration of 20 wt{\%} cooled at 25 degrees C (Gel 25) showed lower fracture stress of 480 kPa. The fracture strain of Gel 25 ranged from 21 to 37{\%} depending on the sPP concentrations. The SEM results revealed that the Gel LN samples had homogeneous networks regardless of the sPP concentrations. The Gel 25, however, possessed inhomogeneous networks with spherulites. It was therefore concluded that the strengthening of the sPP gels could be effectively achieved by Gel LN regardless of the sPP concentrations. [Preview Abstract] |
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P1.00155: Structural Characterization of Layered Morphologies in Precise Copolymers Edward B. Trigg, L. Robert Middleton, Taylor W. Gaines, Kenneth B. Wagener, Karen I. Winey Layered morphologies have been observed in precise polyethylene-based copolymers that contain acid, charged, or polar functional groups precisely spaced along a linear alkane chain. Sufficiently long alkane segments form structures resembling orthorhombic polyethylene crystals, while the functional groups form 2-D layers that disrupt the alkane crystal structure to varying degrees. Here, layered morphologies in precise copolymers containing acrylic acid, phosphonic acid, imidazolium bromide, and sulfone groups are studied via X-ray scattering. Specifically, the composition profiles of the layered structures are obtained by Fourier synthesis, and the coherence length is investigated using peak width analysis. This analysis indicates that the layers of functional groups are frequently bordered by two crystallites, which suggests different dynamics relative to layers bordered by one crystalline and one amorphous microdomain. Detailed understanding of the structure of the layered morphologies will allow for a systematic investigation of proton and ion conductivity mechanisms, which are expected to occur through the high-dielectric layers. [Preview Abstract] |
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P1.00156: Polymer Crystals Formed at Liquid-Liquid Interface Show Broken Symmetry Wenda Wang, Hao Qi, Ziyin Huang, Christopher Y. Li Curved space is incommensurate with typical ordered structures with three-dimensional translational symmetry. However, upon assembly, soft matter, including colloids, amphiphiles, and block copolymers, often form structures depicting curved surface/interface. On the other hand, twisted and curved crystals are often observed in crystalline polymers. Various mechanisms have been proposed for these non-flat crystalline morphologies. In this presentation, we will discuss the recent development of crystallization at flat and curved liquid/liquid (L/L) interface. We show that structure, morphology and chain folding behaviors are strongly affected by L/L interfacial energy and polymer chain ends. Both polyethylene and poly-L-lactic acid single crystal shells have been obtained using curved L/L interface. Polymer crystallization behavior at L/L interface will be compared with solution and bulk crystallization. [Preview Abstract] |
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P1.00157: POLYMER MELTS AND SOLUTIONS |
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P1.00158: Correlating solubility parameters and solvatochromic parameters with the self-assembly of poly(3-hexylthiophene) in mixtures of organic solvents Madeleine Gordon, David Boucher We have studied the assembly and crystallinity of poly(3-hexylthiophene) (P3HT) (M$_{\mathrm{n}} \approx $ 28.2 kDa, regioregularity $>$ 96$\% $, PDI $\approx $ 1.3) in $>$100 binary solvent mixtures using UV-Vis absorption spectroscopy, and it is clear that the identity of the poor solvent used to drive aggregation has a significant impact on the structural order and crystallinity of the P3HT aggregates in solution. Here we report our findings using Hansen solubility parameters (HSPs), specifically the solubility distance vector, R$_{\mathrm{a}}$, and the Kamlet-Taft solvatochromic parameters of the solvent mixtures to better understand the dominant solvent forces driving the self assembly of P3HT. We find that the \textit{directionality} of the R$_{\mathrm{a}}$ vector provides a better measure of the crystallinity of the P3HT assemblies formed in the solvent mixtures than does the \textit{magnitude} of the R$_{\mathrm{a}}$ vector. Our analysis of the Kamlet-Taft ($\alpha $, $\beta $, $\pi $*) and E$_{\mathrm{T}}$(30) solvatochromic parameters reveals that the $\beta $ parameter correlates best with the crystallinity of P3HT and that, in general, assemblies having higher structural order are formed in solvent mixtures with lower values of $\beta$. [Preview Abstract] |
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P1.00159: Demixing transition and molecular interactions in Poly(N-isopropyl acrylamide) solutions compared to its monomer Moritz Futscher, Martine Philipp, Peter Mueller-Buschbaum, Alfons Schulte Temperature-sensitive hydrogels such as poly(N-isopropyl acrylamide) (PNIPAM) exhibit a coil to globule transition of the polymer chains with a lower critical solution temperature (LCST) near 305 K. The cooperative dehydration of bound water molecules upon heating plays a significant role. The hydrogen bonding with the the amide groups in the side chains has to be contrasted with the hydration interaction of the hydrophobic main chain hydro-carbons. Employing FTIR spectroscopy we probe molecular changes in the various chemical groups. PNIPAM and its monomer NIPAM are investigated at a concentration of 20\% in aqueous solution. We observe a nearly discontinuous shift of the the peak frequencies and the intensities of vibrational bands (amides, CH) in PNIPAM, whereas in NIPAM there is a continuous linear shift with temperature. The results are discussed with respect to hydration changes in the amide group and cooperative interactions with bound water along the backbone chain. [Preview Abstract] |
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P1.00160: Pressure and temperature response of Poly(N-isopropyl acrylamide) in aqueous solution probed with Raman microscopy Coleman Cariker, Alfons Schulte Poly(N-isopropylacrylamide) (PNIPAM) is a thermo-responsive hydrogel that exists in a hydrated state beneath its lower critical solution temperature (LCST) near 305 K. Above this temperature water is expelled by the polymer as it undergoes a coil to globule collapse. High pressure is an important variable as it influences the strength of hydrogen bonding and can destabilize hydrophic contacts. We present results from optical imaging on a micron scale and Raman spectroscopic measurements as a function of temperature (295 - 315 K) and hydrostatic pressure (0.1 - 400 MPa). Samples consisted of 25\% PNIPAM in aqueous solution in micro-capillaries with 100 micron cross section. Our experiments reveal differences in the spatial evolution of the phase change across the temperature and pressure transitions. These are corroborated by bond specific and hydration changes observed in the Raman spectra. [Preview Abstract] |
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P1.00161: POLYMERIC ELASTOMERS AND GELS |
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P1.00162: ABSTRACT WITHDRAWN |
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P1.00163: Systematic Investigation of the Mechanical and Surface Properties of Poly(dimethylsiloxane) Networks Matthew Melillo, Zoe Klein, Edwin Walker, Jan Genzer Poly(dimethylsiloxane) (PDMS) is one of the most common elastomers. Its applications range broadly from medical devices to absorbents for water treatment, and recently it has seen rapid growth in the use of microfluidic devices. Despite extensive research and characterization of PDMS networks, the static water contact angles of these elastomers reported in the literature range broadly from a low near 90 degrees upwards to greater than 120 degrees. To investigate this large gap in reported surface properties, we have systematically studied the effects of polymer molecular weight, degree of tetra-functional crosslinker loading, end-group chemical functionality, and the extent of dilution of the curing mixture on the mechanical and surface properties of end-linked PDMS networks. The gel and sol fractions, mechanical properties, and water contact angles have been shown to vary greatly based on the aforementioned variables. This study provides insight to the factors that contribute to such a wide range of surface properties reported in the literature. Furthermore, these results demonstrate the need to fully and carefully consider the manner and environment in which PDMS networks are formed when preparing them for specific applications. [Preview Abstract] |
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P1.00164: Effect of system compliance and indenter geometry on puncture mechanics of soft materials Shruti Rattan, Sami Fakhouri, Alfred Crosby Puncture mechanics in soft materials is critical for the development of new surgical instruments as well as new materials used in personal protective equipment. However, fundamental knowledge of how geometry and material properties control the nucleation of a crack, i.e. puncture, at large deformations in a soft material is currently limited. We describe a simple experimental method to study the resistive forces and failure of a soft gel being indented and punctured with a small needle. We show that puncture stresses can reach two orders of magnitude greater than the material modulus and that the force-deformation response is insensitive to the geometry of indenter at large indentation depths. We determine a transition between stress-limited and energy-limited failure modes, which is governed by the indenter size and the balance between fracture energy and cohesive stress. In addition, we examine the influence of system compliance on puncture of soft gels. It is well-known that system compliance influences the peak force in adhesion and traditional fracture experiments; however, its effect on crack nucleation is unresolved. We find that as the system becomes more compliant lower peak puncture forces were measured, which is associated with increased energy available for fracture. [Preview Abstract] |
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P1.00165: Rheology of Poly($N$-isopropylacrylamide)-Clay Nanocomposite Hydrogels Jack Lombardi, Di Xu, Divya Bhatnagar, Dilip Gersappe, Jonathan Sokolov, Miriam Rafailovich The stiffness of PNIPA Gels has been reported could be significant improved by gelation with clay fillers. Here we conducted systematic rheology study of synthesized PNIPA-Clay Composites at different clay concentration, in a range from fluid to strong gel, where $G''$ dominant changed to $G'$ dominant. Molecular dynamics simulation was employed to analyze the structure of composites and corresponding mechanical changes with increased clays. Where we found viscoelastic behavior become significant only 1.5 times above percolation threshold. The yield stress extrapolated from our rheology results shows good fitting to modified Mooney's theory of suspension viscosity. [Preview Abstract] |
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P1.00166: Self-Assembly and Relaxation Behavior of Graphene Containing Acrylic Triblock Copolymer Gels Mahla Zabet, SeyedMeysam Hashemnejad, Santanu Kundu Investigation of gel mechanical properties as a function of their structure is a significant research interest. This study presents the effect of graphene (or few-layer graphene) on the self-assembly and the relaxation behavior of a thermoreversible gel consists of a physically cross-linked poly (methyl methacrylate)-poly (n-butyl acrylate)-poly (methyl methacrylate) [PMMA-PnBA-PMMA] triblock copolymer in 2-ethyl-1-hexanol, a midblock selective solvent. Graphene was obtained by sonicating exfoliated graphite in 2-ethyl-1-hexanol at various concentrations. Filtration technique and spectrophotometry were utilized to measure the graphene concentration in the dispersions. The dispersed graphene was then incorporated in a series of gels and the effect of graphene on mechanical properties, including the relaxation behavior were studied. Small angle X-ray scattering (SAXS) was used to investigate the microstructure of these gels at room temperature. SAXS data were analyzed to estimate the number of end blocks per junction zone, the average spacing between the junctions, and the change of these properties as a function of graphene concentration. The results indicate that the presence of graphene affects the self-assembly process. [Preview Abstract] |
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P1.00167: POLYMER BLENDS |
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P1.00168: Bottlebrush additives drive formation of vesicle chains in polymer blends Hui Zhen Mah, Pantea Afzali, Rafeal Verduzco, Gila Stein The effects of bottlebrush polymer additive with poly (styrene-r-methyl methacrylate) side-chains on the thin film morphology of polystyrene (PS) and poly (methyl methacrylate) (PMMA) blends were studied. Results were compared to PS/PMMA blends with diblock copolymer PS-b-PMMA compatibilizer and without any additive. Thin films were spin casted from toluene onto a ``neutral'' silicon surface and then annealed at a fixed temperature of 150\textordmasculine C for a range of times (up to 85 mins). The morphology of the films was characterized using optical microscopy and atomic force microscopy. In the absence of any additive, the PS/PMMA blend rapidly de-mixes to form macroscale domains, while high loadings of the PS-b-PMMA additive can compatibilize the blend and suppress phase separation. However, the bottlebrush polymer additive drives the formation of well-organized vesicle chains in the PS/PMMA blend films. This morphology is favored by entropic considerations as the bottlebrush polymers are more stable than linear chains at the PS/PMMA interface and the brush like surface attracts. [Preview Abstract] |
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P1.00169: Phase Equilibria in Ternary Blends of Two Linear Homopolymers and A Ring Gradient Copolymer Dachuan Sun, Junhan Cho Phase equilibria in a ternary blend of linear A/B homopolymers of equal sizes and a symmetric A-co-B ring gradient copolymer as an amphiphile with $\alpha $ as the ratio of their chain sizes are investigated in the mean-field picture. The monomer sequence on the copolymer chain is taken as either a step gradient or a fully linear gradient, to which a gradient number $\lambda = $ 0 or 1 is assigned, respectively. Along the isopleth of equal homopolymer amounts, the resultant phase diagrams for the blends are to be built from multicritical points such as Lifshitz or bulk tricritical point depending on $\alpha $ and $\lambda $. The stabilization of lamellar mesophase or its equilibrium with A and B-rich bulk phases is accordingly controllable by the pair of $\alpha $ and $\lambda $.\\[4pt] This work was supported by the Basic Science Research Program (No. 2014023297) from National Research Foundation of Korea. The authors also acknowledge the support from the Center for Photofunctional Energy Materials, which is funded by Gyeonggi Regional Research Center Program (GRRCdankook2011-B01). [Preview Abstract] |
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P1.00170: ABSTRACT WITHDRAWN |
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P1.00171: COPOLYMERS |
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P1.00172: Characteristic Phase Behaviors for Symmetric PS-b-PAMAs (n= 1?6) and Their Pressure Dependence Yonghoon Lee, Hoyeon Lee, Dong Hyun Lee, Du Yeol Ryu A series of polystyrene-b-poly(alkyl methacrylates) (PS-b-PAMAs) that pertain to the weakly interacting BCP homologues exhibited a variety of phase behaviors by varying alkyl chain length (n) in methacrylate unit. The enthalpic and volumetric changes at phase transitions were measured by the differential scanning calorimetry (DSC) and in-situ spectroscopic ellipsometry with increasing temperature. Together with the overview on the characteristic phase behaviors for symmetric PS-b-PAMAs (n = 1 ? 6), the pressure coefficient (dT/dP) of transition temperatures was calculated on the basis of the Clausius?Clapeyron equation and compared with the reference values. The strong baroplastic character of the closed-loop transitions could be attributed to the significant negative volume changes on mixing at both phase transitions. [Preview Abstract] |
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P1.00173: Orienting Nanostructured Block Copolymer Thin Films via Entropy Ting-Ya Lo, Ashkan Dehghan, Prokopios Georgopanos, Apostolos Avgeropoulos, An-Chang Shi, Rong-Ming Ho Controlling the orientation of nanostructured thin films of block copolymers (BCPs) is essential for next generation lithography using BCPs. According to conventional wisdom, the orientation of BCPs is mainly determined by molecular interactions (enthalpy-driven orientation). Here, we demonstrate that entropic effect can be used to control the orientation of BCP thin films. Specifically, the architecture of star-block copolymers consisting polystyrene (PS) and poly(dimethylsiloxane) (PDMS) blocks is used to regulate the entropic contribution to the self-assembled nanostructures. Our experimental and theoretical results unequivocally demonstrate that entropy-driven perpendicular orientation of BCP nanostructures can be induced by increasing the arm number of the star-block copolymers with the same volume fractions of PS and PDMS. [Preview Abstract] |
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P1.00174: A Facile Method to Fabricate Double Gyroid as A Polymer Template for Nanohybrids Hsiao-Fang Wang, Rong-Ming Ho Here, we suggest a facile method to acquire double gyroid (DG) phase from the self-assembly of chiral block copolymers (BCPs*), polystyrene-$b$-poly(L-lactide) (PS-PLLA). A wide region for the formation of DG can be found in the phase diagram of the BCPs*, suggesting that helical phase (H*) from the self-assembly of BCPs* can serve as a stepping stone for the formation of the DG due to an easy path for order-order transition from two-dimensional to three-dimensional (network) structure. Moreover, the order-order transition from metastable H* to stable DG can be expedited by blending the PS-PLLA with compatible entity. Moreover, PS-PLLA blends are prepared by using styrene oligomer (S) to fine-tune the morphologies of the blends at which the molecular weight ratio of the S and compatible PS block ($r)$ is less than 0.1. Owing to the use of the low-molecular-weight oligomer, the increase of BCP chain mobility in the blends significantly reduces the transformation time for the order-order transition from H* to DG. Consequently, nanoporous gyroid SiO$_{\mathrm{2}}$ can be fabricated using hydrolyzed PS-PLLA blends as a template for sol-gel reaction followed by removal of the PS matrix. [Preview Abstract] |
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P1.00175: Selective Permeating Properties of Butanol and Water through Polystyrene-$b$-polydimethylsiloxane-$b$-polystyrene Pervaporation Membranes Chaeyoung Shin, Zachary Baer, X. Chelsea Chen, A. Evren Ozcam, Douglas Clark, Nitash Balsara Polystyrene-$b$-polydimethylsiloxane-$b$-polystyrene (SDS) membranes have been studied in butanol-water binary pervaporation experiments and pervaporation experiments integrated with viable fermentation broths. Polydimethylsiloxane has been widely known to be a suitable material for separating organic chemicals from aqueous solutions, and it thus provides a continuous matrix phase in SDS membranes for permeation of small molecules. The polystyrene block provides mechanical stability to maintain the membrane structure in the pervaporation membranes. We take advantage of these features to fabricate a thin and butanol-selective SDS membrane for \textit{in situ} product removal in fermentation. [Preview Abstract] |
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P1.00176: Effect of Asymmetric Confinement on the Microdomain Morphology of Block Copolymers Youngkeol Kim, Guiduk Yu, Kookheon Char Nanometer scale confinement could impose constraints to change the bulk equilibrium behavior of block copolymers (BCPs). The self-assembly of BCPs confined by two parallel surfaces (one-dimensional confinement) has been both theoretically and experimentally studied. More recently, cylindrical pores where the diameter of the pores are only several repeat periods of the copolymers have been employed to investigate the influence of two-dimensional confinement on the behavior of BCPs. However, the analysis on confinement by asymmetric geometry has not been thoroughly studied yet. Given the size of confining channels, singularity arising from the asymmetric geometry such as triangles and squares, could have a significant effect on the structure and symmetry of BCP morphologies self-assembled within such confinement. We prepared AAOs with triangular pores based on aluminum substrates with inverse-hexagonal packing pattern. Based on the detailed observation of BCP self-assembly within porous triangular columns, we analyzed the structural transition of BCPs induced by asymmetric confinement. Furthermore, we found that the packing frustration imposed by such confinement could be released by adding homopolymers into the BCP system. [Preview Abstract] |
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P1.00177: Synthesis of zwitterionic polymer-based amphiphilic triblock copolymers by atom transfer radical polymerization for production of extremely stable nanoemlusions Jin Yong Lee, Ji Eun Kim, Jin Woong Kim In fields of soft matter, there have been growing interests in utilizing amphiphilic block copolymers due to their intriguing properties, such as surface activity as well as self-assembly. In this work, we synthesize a series of poly (2-(methacryloyloxy) ethyl phosphorylcholine)-$b$-poly ($\varepsilon $-caprolactone)-$b$-poly (2-(methacryloyloxy) ethyl phosphorylcholine) (PMPC-$b$-PCL-$b$-PMPC) triblock copolymers by using atom transfer radical polymerization (ATRP). We have a particular interest in using poly (2-(methacryloyloxy) ethyl phosphorylcholine) (PMPC) as a hydrophilic block, since it can have both electrostatic repulsion and steric repulsion in complex fluid systems. Assembling them at the oil-water interface by using the phase inversion method enables production of highly stable nanoemulsions. From the analyses of the crystallography and self-assembly behavior, we have found that the triblock copolymers assemble to form a flexible but tough molecular thin film at the interface, which is essential for the remarkable improvement in the emulsion stability. [Preview Abstract] |
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P1.00178: Ab initio molecular dynamics simulations of the thermal degradation of model compounds of industrially-relevant copolyesters Erol Yildirim, Andrew T. Detwiler, Curt Cleven, Ahmed El-Shafei, Melissa A. Pasquinelli The thermal degradation of copolyesters can be impacted by a variety of factors beyond the chemical composition of the polymer, including the solvent and processing conditions, as well as the presence of oxygen, moisture, additives, and dyes. Thus, we investigated the role that these factors play for a series of model compounds of industrially relevant copolyesters using ab initio molecular dynamics simulations. The results reveal some interesting trends and correlations to experiments, which can be applied to improve the exterior longevity of copolyesters. [Preview Abstract] |
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P1.00179: Resonant Soft X-ray Scattering for Soft Materials Cheng Wang, Athony Young, Alexander Hexemer, Howard Padmore Over the past a few years, we have developed Resonant Soft X-ray Scattering (RSoXS) and constructed the first dedicated resonant soft x-ray scattering beamline at the Advanced Light Source, LBNL. RSoXS combines soft x-ray spectroscopy with x-ray scattering thus offers statistical information for 3D chemical morphology over a large length scale range from nanometers to micrometers. Its unique chemical sensitivity, large accessible size scale, molecular bond orientation sensitivity with polarized x-rays and high coherence have shown great potential for chemical/morphological structure characterization for many classes of materials. Some recent development of in-situ soft x-ray scattering with in-vacuum sample environment will be discussed. In order to study sciences in naturally occurring conditions, we need to overcome the sample limitations set by the low penetration depth of soft x-rays and requirement of high vacuum. Adapting to the evolving environmental cell designs utilized increasingly in the Electron Microscopy community, customized designed liquid/gas environmental cells will enable soft x-ray scattering experiments on biological, electro-chemical, self-assembly, and hierarchical functional systems in both static and dynamic fashion. Recent RSoXS results on organic electronics, block copolymer thin films, and membrane structure will be presented. [Preview Abstract] |
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P1.00180: CHARGED AND ION-CONTAINING POLYMERS |
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P1.00181: Complexation between Charged Dendrimers and Polyelectrolytes Gunja Pandav, Venkat Ganesan We extend the single chain in mean field simulation framework to treat charged nanoparticles in polyelectrolyte solution in presence of explicit counterions and salt. We use two models to depict nanoparticles, viz., soft nanoparticles in the form of dendrimers and hard nanoparticles having impenetrable core and penetrable outer shell. For both models, a systematic analysis of properties of complexes formed due to electrostatic interactions is carried out using radial distribution functions, charge distribution, complex size distribution, etc. In addition, we also comment on the structure of complexes formed as a function of charge on nanoparticles and polyelectrolytes. [Preview Abstract] |
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P1.00182: The effect of multivalent ions on the thermal transition of hydrated polyelectrolyte multilayers Dariya Reid, Jodie Lutkenhaus Layer-by-layer (LbL) assembly is a commonly studied technique in the production of uniform thin films. Hydrate LbL assemblies made of model polyelectrolytes, poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate) (PSS), exhibit a thermal transition with features of a glass transition and a lower critical solution temperature transition when assembled in the presence of sodium chloride. The question remains as to how multivalent cations affect the nature of the transition. Here, we present results on the thermal transition of PDAC/PSS LbL assemblies exposed to various multivalent salts. Quartz crystal microbalance (QCM-D) and modulated differential scanning calorimetry (MDSC) is used to assess the transition. [Preview Abstract] |
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P1.00183: Phase Behavior and Conductivity of Phosphonated Block Copolymers Containing Ionic Liquids Ha Young Jung, Sung Yeon Kim, Moon Jeong Park As the focus on proton exchange fuel cells continues to escalate in the era of alternative energy systems, the rational design of sulfonated polymers has emerged as a key technique for enhancing device efficiency. While the sulfonic acid group guarantees high proton conductivity of membranes under humidified conditions, the growing need for high temperature operation has discouraged their practical uses in fuel cells. In this respect, phosphonated polymers have drawn intensive attention in recent years owing to their self-dissociation ability. In this study, we have synthesized a set of phosphonated block copolymers, poly(styrenephosphonate-methylbutylene) (PSP-$b-$PMB), by varying phosphonation level (PL). A wide variety of self-assembled morphologies, i.e., disordered, lamellar, hexagonally perforated lamellae and hexagonally packed cylindrical phases, were observed with PL. Remarkably, upon comparing the morphology of PSP-$b$-PMB and that of sulfonated analog, we found distinctly dissimilar domain sizes at the same molecular weight and composition. A range of ionic liquids (ILs) were incorporated into the PSP-$b$-PMB block copolymers and their ion transport properties were examined. It has been revealed that the degree of confinement of ionic phases (domain size) impacts the ion mobility and proton dissociation efficiency of IL-containing polymers. [Preview Abstract] |
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P1.00184: Molecular Dynamics of Coarse-grained Ionomers Showing Aggregate Morphology During Deformation Janani Sampath, Lisa M. Hall Ionomers are polymers with a small fraction of charged monomers that have a wide range of applications from dental fixtures and packaging to actuators. We consider dense melts of ionomers and counterions with no solvent. An important aspect of their performance is the aggregation of ions, since ionic aggregates act to hold polymer chains together like temporary cross-links. Because of the size scales involved, it is difficult to obtain a complete 3D microscopic picture of polymer aggregation experimentally; typically the thickness of a sample used in transmission electron microscopy is such that multiple overlapping aggregates appear together. How aggregate structure changes under strain and affects mechanical properties is even less clear. We perform molecular dynamics simulations of ionomers of various architectures, and show aggregate morphology and scattering profiles. We apply uniaxial tensile strain and observe the aggregates align, in qualitative agreement with experimental findings. We also obtain stress-strain curves and will discuss effects of degree of neutralization of the ionomers. [Preview Abstract] |
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P1.00185: Effects of Acid and Ionic Aggregation on the Polymer Dynamics in Precise Ionomers Luri Robert Middleton, Jacob Tarver, Jason Azoulay, Dustin Murtagh, Ken Wagener, Joseph Cordaro, Madhu Tyagi, Christopher Soles, Karen Winey Interest in acid- and ion-containing polymers arises from applications as single-ion conductors for selectively transporting a counter ion of the opposite charge for energy applications. The relatively low dielectric constant of the organic polymer and strong ionic interactions leads to ionic aggregation. Ion aggregation anchors the polymer chain, decreasing the mobility of the ion and the polymer. In precise poly(ethylene-acrylic acid) copolymers and ionomers (pxAA-{\%}Li) we report on the effect of carbon spacer length (x$=$9, 15, 21) between the acid groups and the effect of the percent of acid groups neutralized with Li on backbone dynamics. The polymer backbone motion is investigated through quasi-elastic neutron scattering measurements. At nano-second timescales a single relaxation fits the data. Systematic changes in dynamics were observed with increasing neutralization percent where polymer dynamics are confined due to anchoring effects. Intriguingly, systematic changes in the spacer lengths did not result in similar behavior. At pico-second timescales multiple overlapping relaxations are observed but even at these short timescales systematic changes in atomic motion are observed with ion content. [Preview Abstract] |
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P1.00186: Structure and Proton Conductivity in Mixtures of Poly(acrylic acid) and Imidazole Han-Chang Yang, Philip J. Griffin, Karen I. Winey Proton conductivity in polymer electrolyte membranes (PEMs) typically involves water, which requires that during operation the humidity of the PEM be carefully controlled. In contrast, anhydrous protic polymer membranes promote proton transport by incorporating heterocyclic molecules, such as imidazole and its derivatives, into acid-containing polymers. In this work, we explore the interplay between nanoscale-structure and proton conduction of poly(acrylic acid) (PAA) blended at varying compositions with 2-ethyl-4-methylimidazole (EMI). We present the glass transition temperature from differential scanning calorimetry, morphology characterization from X-ray scattering, and proton conductivity from electrical impedance spectroscopy. [Preview Abstract] |
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P1.00187: pH-Responsive Behavior of Poly(acrylic acid) Brushes of Varying Thickness Vivek Yadav, Megan Robertson, Jacinta Conrad We have investigated the pH-dependent response of polyelectrolyte brushes of varying thickness. Our model system consists of poly(acrylic acid) brushes, which change from hydrophobic and neutral at low pH to hydrophilic and negatively charged at high pH, synthesized using a grafting-from approach at constant grafting density. As the polymer brush thickness increased, the brushes exhibited greater hysteresis in static water contact angle as a function of pH. We extracted the pKa of the polymer brushes from contact angle measurements. The relationship between the pKa and brush thickness depended on the order in which the brushes were exposed to solutions of varying pH: pKa decreased on increasing brush thickness when going from basic to acidic medium whereas pKa increased on increasing brush thickness when going from acidic to basic medium. We speculate that the origin of hysteresis can be explained by pH-dependent conformational changes in these polyelectrolyte brushes. [Preview Abstract] |
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P1.00188: Influence of Hydration Level on Polymer and Water Dynamics in Alkaline Anion Exchange Fuel Cell Membranes Jacob Tarver, Jenny Kim, Madhu Tyagi, Christopher Soles, Tsung-Han Tsai, Bryan Coughlin Triblock copolymers based on poly(chloromethylstyrene)-b-poly(ethylene)-b-poly(chloromethylstyrene) can be quaternized to different extents to yield anion exchange membranes for alkaline fuel cells. In the absence of moisture, these membranes demonstrate bilayer lamellar morphology. Upon high levels of hydration, however, in-situ small angle neutron scattering reveals the emergence of higher-order diffraction peaks. This phenomena has previously been observed in analogous diblock copolymer-based membranes and has been attributed to the induction of a multilayer lamellar morphology in which selective striping of water occurs in the center of the ion-rich domain. By conducting humidity-resolved quasielastic neutron scattering (QENS) measurements using deuterated water, we are able to isolate differences in the pico- to nanosecond timescale dynamics of the hydrogenated membrane upon hydration. QENS measurements in the presence of a hydrogenated water source subsequently permit deconvolution and isolation of the translational and rotational dynamics of water as a function of relative humidity, revealing spatial and temporal changes in polymer and water motion at high levels of hydration. [Preview Abstract] |
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P1.00189: Understanding the impact of nanoscale aggregation on charge transport and structural dynamics in room temperature ionic liquids Philip Griffin, Adam Holt, Yangyang Wang, Alexei Sokolov Amphiphilic room temperature ionic liquids (ILs) segregate on the nanoscale, forming intricate networks of charge-rich ionic domains intercalated with charge-poor aliphatic domains. While this structural phenomenon has been well established through x-ray diffraction studies and atomistic MD simulations, the precise effects of nanophase segregation on ion transport and structural dynamics in ILs remains poorly understood. Using a combination of broadband dielectric spectroscopy, light scattering spectroscopy, and rheology, we have characterized the ionic conductivity, structural dynamics, and shear viscosity of a homologous series of quaternary ammonium ionic liquids over a wide temperature range. Upon increasing the length and volume fraction of the alkyl side chains of these quaternary ammonium ILs, ionic conductivity decreases precipitously, although no corresponding slowing of the structural dynamics is observed. Instead, we identify the dynamical signature of supramolecular aggregates. Our results directly demonstrate the role that chemical structure and ionic aggregation plays in determining the charge transport properties of amphiphilic ILs. [Preview Abstract] |
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P1.00190: Spray-assisted layer-by-Layer (LbL) assembly of anisotropic materials Souvik De, Pilar Suarez Martinez, Avanti Kavarthapu, Jodie Lutkenhaus Layer-by-layer (LbL) assembly has gained tremendous interest as it allows one to incorporate a large variety of molecules with nano-scale precision and very good reproducibility. In addition to charged polymers, the technique has become extremely popular to fabricate tailor-made thin films containing anisotropic nanomaterials (e.g., graphene oxide sheets). The challenge is that a standard protocol to fabricate ``all-polyelectrolyte'' LbL films may not necessarily give rise to satisfactory film growth when applied to LbL assembly where one of the adsorbing components is an anisotropic nanomaterial. Therefore, in this contribution, we combine polymers and anisotropic nanomaterials via dip- and spray-assisted LbL assembly and investigate the effect of charge density, exfoliation, concentration etc. of the components on the growth behavior and the film quality. The end result is a conformal, pin-hole free coating on model substrates (glass, silicon, metal) over a large area. [Preview Abstract] |
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P1.00191: Morphology and charge transport in ammonium based polymerized ionic liquids Maximilian Heres, Joseph Minutolo, Jacob Shamblin, Maik Long, Stefan Berdzinski, Veronika Stremel, Joshua Sangoro Ionic conduction, structural dynamics and morphology in a series of ammonium based polymerized ionic liquids are investigated using broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, and neutron as well as x-ray scattering techniques. The dielectric spectra are dominated on the low frequency regime by electrode polarization while hopping conduction is the underlying mechanism at higher frequencies. At their respective calorimetric glass transition temperatures, a strong correlation between the morphology and ionic conductivity is found. These results are discussed within the recent approaches proposed to explain the decoupling of charge transport from structural dynamics. [Preview Abstract] |
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P1.00192: Effect of Supercharging on Coacervation Between Proteins and Polyelectrolytes Bradley Olsen, Allie Obermeyer, Carolyn Mills, Xuehui Dong Complex coacervates have attracted a great deal of attention as a method to encapsulate biological molecules including DNA and proteins. However, a large fraction of proteins will not form coacervates with oppositely charged polymers unless their surface charge density is increased through a process known as supercharging. Using mass spectrometry, we are able to quantify the formal charge distribution of proteins after supercharging, and with this knowledge of the chemical state of the protein measure coacervate formation for a panel of proteins as a function of charge. While many of the proteins studied do not form coacervates or coacervate over only a narrow range of composition in their native form, all proteins form coacervates above a critical charge level with increasing range of coacervation as surface charge density increases. The resulting data is consistent with a strong induced charging effect in the coacervate state, as the largest coacervate forms near a charge ratio corresponding to proteins at their maximum charge. These observations in bulk coacervation are translated to the design of coacervate core micelles, providing an increased quantitative understanding of structure formation in these systems. [Preview Abstract] |
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P1.00193: RENEWABLE AND SUSTAINABLE POLYMERS |
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P1.00194: Synthesis and Characterization of Branched Poly(ester urea)s with Different Branch Density Jiayi Yu, Matthew Becker A new class of $L$-phenylalanine-based poly(ester urea)s (PEU) was developed that possess tunable mechanical properties, water uptake ability and degradation rates. Our preliminary data has shown that 1,6-hexanediol $L-$phenylalanine-based poly(ester urea)s possesses an elastic modulus nearly double that of poly(lactic acid). My work details the synthesis of a series of $L-$phenylalanine-based poly(ester urea)s possessing a variation in diol chain length and in branch density and shows how these subtle structural differences influence the mechanical properties and \textit{in vitro} biodegradation rates. The elastic moduli span a range of values that overlap with several currently clinically available degradable polymers. Increasingly the diol chain lengths increases the amount of flexible segment in the chemical structure, which results in reduced elastic modulus values and increased values of elongation at break. Increasing the amount of branch monomer incorporated into the system reduces the molecular entanglement, which also results in decreased elastic modulus values and increased values of elongation at break. The $L-$phenylalanine-based poly(ester urea)s also exhibited a diol length dependent degradation process that varied between 1-5 {\%} over 16 weeks. Compared with PLLA, PEUs degrade more quickly and the rate can be tuned by changing the diol chain length. PEUs absorb more water and the water uptake ability can be tuned by changing the branch density. [Preview Abstract] |
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P1.00195: APPLID POLYMER PHYSICS AND ADVANCED MANUFACTURING |
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P1.00196: Spray Deposition of Multilayer Gas Barrier Thin Films Tara Givens, Fangming Xiang, Jaime Grunlan Dip-assisted assembly is the norm for making multilayer thin films (also known as layer-by-layer [LbL] assembly). Spray-based deposition possesses several advantages over dipping, but has not been studied in great detail, especially for gas barrier layers. In this study, polyethylenimine [PEI]/poly(acylic acid) [PAA] bilayers were deposited with varying spray parameters. Spraying time was found to be the most influential parameter to control the roughness, thickness, and gas barrier of the PEI/PAA assembly. A spray-coated sample was prepared using optimized parameters and compared to a dip-coated sample using the same deposition time (5s). The sprayed sample was better in terms of thickness, roughness, and gas barrier. This study is the first report showing that a sprayed multilayer assembly has better properties than its dipped counterpart. These findings could revolutionize the multilayer deposition process, making it more commercially-friendly. [Preview Abstract] |
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P1.00197: Inexpensive Fabrication of Metallic Interconnects on Flexible Substrates Aditi Naik, Rohit Kothari, James Watkins Sub-micron metallic interconnects on flexible substrates are important to produce inexpensive bendable devices and electronics. The key component hindering high-performance flexible electronics is the lack of high transistor integration density. Previous researchers have created solution-processable semiconductor and dielectric layers; however, sub-micron solution-processable copper electrodes have yet to be developed. Using cost-effective processing techniques, including soft nanolithography and photonic sintering, with a commercial copper oxide ink, we have demonstrated the fabrication of sub-micron copper interconnects on glass and plastic substrates. This inexpensive, solution-processable method is amenable to high-speed printing over large areas by roll-to-roll processing and will lead to the development of low-cost flexible electronics. [Preview Abstract] |
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P1.00198: A Molecular Perspective of Inter-filament Bonding in Fused Deposition Modeling 3-D Printing Edward Duranty, Brandon Spradlin, Mark Dadmun Fused deposition 3D printing is an important tool for low-cost and rapid prototyping of objects with complex geometries. 3D printed materials are composed of many filaments deposited on a heated substrate, requiring the bonding of neighboring filaments during the deposition process. Filament deposition often creates voids between filaments, which requires necking between them to create a robust sample. Therefore the amount of interfacial contact and interdiffusion between filaments become important parameters that control the macroscopic physical properties of the printed prototype. Our research focuses on quantifying the interfacial adhesion between ABS filaments and its impact on structural properties. The time evolution of the temperature profile near the heated substrate demonstrates that the deposited filaments are repeatedly heated above the Tg of ABS allowing interpenetration of the polymer chains between adjacent filaments. Results of DMA experiments on samples of different geometries have been correlated to microphotography that monitors the degree of necking between filaments and the thermal history. Results indicate that interfacial contact area between filaments and increased thermal energy are crucial to their mechanical properties. [Preview Abstract] |
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P1.00199: THEORY AND SIMULATION OF MACROMOLECULES |
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P1.00200: Contrasting Polymer Behavior Under Nanoconfinement using Thermomechanically Consistent Coarse-Grained Models Sinan Keten, Wenjie Xia, David Hsu We present a systematic, two-bead per monomer coarse graining strategy that simulates the thermomechanical behavior of polymers several hundred times faster than all-atom MD (Hsu et al. JCTC, 2014). The predictive capability of the technique is illustrated here for 5 different methacrylate monomers and polystyrene stereoisomers. The approach involves optimization of analytical bonded potentials from atomistic bonded distributions to emulate local structure, as validated by chain end-to-end length and the radius of gyration comparisons with experiments and random coil theory. Nonbonded Lennard-Jones potentials are tuned to reproduce the elastic modulus (E) and glass transition temperature (T$_{g})$ at a single thermodynamic state. Density-corrected parameters capture temperature-modulus dependence in the 150-600 K range. Flory-Fox constants of the CG models are commensurate with all atomistic and experimental results, even though all calibrations are done at a single molecular weight. Finally, we further demonstrate the predictive capabilities of the models by examining thin film nanoconfinement effects for different polymers, film thicknesses, interfacial energies, and molecular weights. Our technique, called thermomechanically consistent coarse graining (TCCG), is demonstrated, using polystyrene and poly(methylmethacrylate) as universal benchmarks, to be a robust and effective technique to understand the thermomechanical behavior of polymers thin films and nanocomposites. [Preview Abstract] |
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P1.00201: ABSTRACT WITHDRAWN |
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P1.00202: Coarse-Graining in Simulations of Multicomponent Polymer Systems Vaidyanathan Sethuraman, Venkat Ganesan We investigate the mapping required between the interaction parameters of two different coarse-grained simulation models to ensure a match of the long-range structural characteristics of multicomponent polymeric system. We investigate the extensibility of mapping functions deduced in the context of symmetric block copolymers by Morse and coworkers to other polymeric systems by studying a variety of systems, including, asymmetric diblock copolymers, symmetric triblock copolymers and diblock copolymer-solvent mixtures. We observe excellent agreement for peak in the inverse structure between two popular coarse grained models for all sets of polymeric melt systems investigated, thus showing that the mapping function proposed for diblock copolymer melts is transferable to other polymer melts irrespective of the blockiness or overall composition. We use our findings to propose a methodology to create ordered morphologies in simulations involving hard repulsive potentials in a computationally efficient manner. [Preview Abstract] |
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P1.00203: Structural analysis of liquid crystalline order in polymer melts and blends Kiran Khanal, Jutta Luettmer-Strathmann Blends of liquid crystalline and flexible polymers have interesting physical behaviors and important applications in organic electronics. We investigate the liquid crystalline transition in melts and blends of semiflexible polymers with Monte Carlo simulations of a bond fluctuation lattice model. For polymer melts we study the influence of attractive interactions on the isotropic to nematic phase transition for different polymer concentrations. We observe that the structure of the ordered phase is different for melts with and without attractive interactions. We construct the phase diagram and find the transition temperature increases with increasing strength of the attractive interaction. To analyze the structure of ordered and disordered regions in polymer melts and blends, we calculate a set of pair distribution functions. We also investigate the effect of an ordering field on the liquid crystalline order in polymer melts and blends. [Preview Abstract] |
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P1.00204: Size and Shape Descriptors of Two Dimensional Polymer Sheets in Solution near the Crossover Concentration Salomon Turgman Cohen, Jacobi Tanner We investigate the size and shape of two dimensional polymer sheets near the crossover concentration as a function of sheet size and concentration. Specifically, fully flexible sheets with local square connectivity in implicit, athermal solvent are investigated by molecular dynamics simulations in the NVT ensemble with a Lagevin thermostat. Sheet sizes of $N = 100, 400$, and $1600$ are explored. We monitor the average radius of gyration ($R_g$) tensor and the relative shape anisotropy around the cross-over concentration. Opposite to linear, one dimensional polymers, preliminary results show that the size of the sheets as measured by the average radius of gyration increases as the cross-over concentration is approached. The trends in the relative shape anisotropy suggest that the increasing overlap between the sheets at high concentrations leads to the sheets favoring flatter conformations, explaining the larger values of $R_g$ observed. [Preview Abstract] |
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P1.00205: The effect of copolymers on the interfaces in incompatible homopolymers blend: Molecular dynamics study Jiho Ryu, Won Bo Lee Using molecular dynamics simulations the effect of copolymers as compatibilizer for reducing interfacial tension and enhancement of interfacial adhesion at the interface of thermodynamic unfavorable homopolymers blend is studied with block- and graft-copolymers. We have calculated local pressure tensor of system along the axis perpendicular to interface, varying bending potential energy of one part, which consist of just one kind of beads, of copolymer chain to examine the effect of stiffness of surfactin molecules. Here we consider symmetric diblock copolymer (f$=$1/2) having 1/2 N make of beads of type A and the other part made of beads of type B, and graft copolymer having backbone linear chain consist of 1/2 N beads of type of A and branched with two side-chain consist of 1/4 N beads of type B. All simulations were performed under the constant NPT ensemble at T*$=$1, $\rho$*$\sim$0.85. Also we studied changes of effect of copolymers with increasing pairwise repulsive interaction potential between two beads of types A and B while homopolymers chain length are fixed, N$=$30. [Preview Abstract] |
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P1.00206: Monte Carlo Simulations on Phase Transitions and Conformational Properties of Catenated Double-ring Copolymers Dachuan Sun, Junhan Cho The thermodynamic and conformational properties of catenated double-ring A/B copolymer melts are investigated through lattice Monte Carlo simulations. The topological constraint on the catenated copolymers is shown to suppress demixing of A and B monomers. This action results in their order-to-disorder transition (ODT) at an increased segregation level and the lamellae below ODT with reduced order, when compared to diblock copolymers of linear or single-ring topology. The A and B rings are pulled closer by catenation in the copolymer, which leads to its smaller gyration radius, lamellar domain spacing, and distance between mass centers of the two rings than for the diblock copolymers. With increasing segregation tendencies, the gyration radii of the A rings of the catenated copolymers stretch along the direction normal to lamellae, while the A-block conformations of the single-ring copolymers change their shapes from ellipsoid to sphere.\\[4pt] This work was supported by the Basic Science Research Program (No. 2014023297) from National Research Foundation of Korea. The authors also acknowledge the support from the Center for Photofunctional Energy Materials, which is funded by Gyeonggi Regional Research Center Program (GRRCdankook2011-B01). [Preview Abstract] |
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P1.00207: Using graphs to interrogate the atomic structure of polymer blends Olga Wodo, Baskar Ganapathysubramanian The nanomorphology of polymer blend thin films critically affects performance especially in electronic devices. However, many aspects of the underlying physics linking morphology to performance are still poorly understood. Furthermore, there is increasing evidence that atomic organization can hold the key to efficient charge transport within organic electronic devices. In this work, we take advantage of recent advances in molecular dynamic simulations and quantify atomic-scale morphological aspects of the thin films. Specifically, we present a graph-based technique that allows quantifying the point-cloud data. In our approach, we first convert the point cloud data from atomistic simulation into a labelled, weighted, undirected graph and then use standard graph-based algorithms to calculate and quantify morphology features. The conversion of the CGMD-data into a graph preserves all the topological and geometric information about the internal structure, and local connectivity between individual atoms/beads (along and across the polymer chains). Our method provides hierarchical information about the charge paths that a hole/electron needs to take to reach the electrode (path length, fraction of intra-molecular hops, path balance). We showcase capabilities of our approach by analyzing coarse grained molecular simulations, and quantifying effect of various thermal treatment as well as electrode materials on the P3HT:PCBM blend. [Preview Abstract] |
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P1.00208: An atomistic model for cross-linked HNBR elastomers used in seals Nicola Molinari, Adrian Sutton, John Stevens, Arash Mostofi Hydrogenated nitrile butadiene rubber (HNBR) is one of the most common elastomeric materials used for seals in the oil and gas industry. These seals sometimes suffer ``explosive decompression,'' a costly problem in which gases permeate a seal at the elevated temperatures and pressures pertaining in oil and gas wells, leading to rupture when the seal is brought back to the surface. The experimental evidence that HNBR and its unsaturated parent NBR have markedly different swelling properties suggests that cross-linking may occur during hydrogenation of NBR to produce HNBR. We have developed a code compatible with the LAMMPS molecular dynamics package to generate fully atomistic HNBR configurations by hydrogenating initial NBR structures. This can be done with any desired degree of cross-linking. The code uses a model of atomic interactions based on the OPLS-AA force-field. We present calculations of the dependence of a number of bulk properties on the degree of cross-linking. Using our atomistic representations of HNBR and NBR, we hope to develop a better molecular understanding of the mechanisms that result in explosive decompression. [Preview Abstract] |
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P1.00209: Pattern Recognition of Adsorbing HP Lattice Proteins Matthew S. Wilson, Guangjie Shi, Thomas W\"ust, David P. Landau, Friederike Schmid Protein adsorption is relevant in fields ranging from medicine to industry, and the qualitative behavior exhibited by course-grained models could shed insight for further research in such fields. Our study on the selective adsorption of lattice proteins utilizes the Wang-Landau algorithm to simulate the Hydrophobic-Polar (H-P) model\footnote{K. A. Dill, Biochemistry 24, 1501 (1985); K. F. Lau and K. A. Dill, Macromolecules 22, 3986 (1989).} with an efficient set of Monte Carlo moves\footnote{T. W\"ust and D. P. Landau, Phys. Rev. Lett. 102, 178101 (2009); J. Chem. Phys. 137, 064903 (2012).}. Each substrate is modeled as a square pattern of 9 lattice sites which attract either H or P monomers, and are located on an otherwise neutral surface. The fully enumerated set of 102 unique surfaces is simulated with each protein sequence. A collection of 27-monomer sequences\footnote{M. Mann, D. Maticzka, R. Saunders, and R. Backofen. HFSP Journal 2. 396. Special issue on protein folding: experimental and theoretical approaches.(2008).} is used-- each of which is non-degenerate and protein-like. Thermodynamic quantities such as the specific heat and free energy are calculated from the density of states, and are used to investigate the adsorption of lattice proteins on patterned substrates. [Preview Abstract] |
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P1.00210: Calculating Pressure and Surface Tension of Lattice Polymers Qiang Wang, Pengfei Zhang Calculating pressure and related surface tension of polymeric systems in lattice Monte Carlo simulations is an important but nontrivial subject. Here we propose several novel, efficient, and accurate methods. In the first method, we combine chain insertion/deletion with the Wang-Landau -- Optimized Ensemble (WL-OE) simulation, which is very efficient at low to intermediate polymer volume fractions $\varphi $. In the second method, we introduce a repulsive plane with bridging bonds, which is similar to the repulsive wall method but eliminates its confinement effects. This method works especially well at \textit{high} $\varphi $ where all the methods using chain insertion/deletion fail. Finally, we combine the above two methods, which gives complete thermodynamics over the \textit{entire} range of continuous and exact $\varphi $-values with negligible finite-size effects. To demonstrate our methods, we apply them to calculate the bulk pressure and surface tension of nano-confined homopolymers. [Preview Abstract] |
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P1.00211: Protein-like folding and other phase transitions of a single polymer chain Mark Taylor, Wolfgang Paul, Kurt Binder A single polymer chain can undergo a series of conformational transitions analogous to the phase transitions exhibited by bulk materials. We have recently studied the conformational transitions of a flexible square-well polymer chain using a Wang-Landau simulation approach in which we directly compute the single-chain partition function [1]. For the case of a tangent-sphere chain, the temperature-interaction range phase diagram includes both a coil-globule and globule-crystal transition as well as an ``all-or-none'' coil-crystal transition. Despite the non-unique homopolymer ground state, the thermodynamics of this direct freezing transition are identical to the thermodynamics of two-state protein folding. Two-dimensional configurational and free energy landscapes reveal both a dominant ``folding'' pathway and a ``dead-end'' pathway resulting in a bimodal distribution of structures at the top of the free energy barrier. A simple AB-heteropolymer variant of this model leads to both rod-like and disk-like ground state structures while a fused sphere version of the model produces helical folded structures.\\[4pt] [1] M.P. Taylor, W. Paul, and K. Binder, Polymer Science Ser. C 55, 23 (2013). [Preview Abstract] |
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P1.00212: Simulation of dynamics of disordered diblock copolymers near the order-disorder transition Pavani Medapuram, David Morse We present a simulation study of the dynamics of composition fluctuations, chain conformations and stress for diblock copolymers near the order-disorder transition. Specifically, we study the behavior of the van Hove function S(q,t), which is a measure of structural relaxation, the linear response of the bond orientation tensor, which is closely related to optical birefringence, and the linear viscoelastic stress relaxation modulus G(t). We show how a slowly decaying mode associated with slow relaxation of composition fluctuations emerges as the degree of segregation is increased. [Preview Abstract] |
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P1.00213: Conformation of Single Polymer Chains Howard Wang, Xiaorong Wang Large biological molecules such as proteins and DNAs can be packed into condensed forms through hydrogen bonding and specific interactions; the conformation of an ultra-long single chain with no specific intra-chain interactions is considered here. We discuss three possible states, (1) uniformly compressed Gaussian, (2) totally irregular aggregates, and (3) long Gaussian sections separated by segments of frustrated local conformation, or ``kinks.'' Those states could be related to the methods of preparing the condensed form of the single chain globule. We argue that the Gaussian-Kink conformation is preferred and the segregation of kinks to the surface of globules would significantly alter the chain dynamics. [Preview Abstract] |
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P1.00214: BIOPOLYMERS AND BIOHYBRID POLYMERS |
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P1.00215: Binding Affinity Effects on Physical Characteristics of a Model Phase-Separated Protein Droplet Sara Chuang, Salman Banani, Michael Rosen, Clifford Brangwynne Non-membrane bound organelles are associated with a range of biological functions. Several of these structures exhibit liquid-like properties, and may represent droplets of phase-separated RNA and/or proteins. These structures are often enriched in multi-valent molecules, however little is known about the interactions driving the assembly, properties, and function. Here, we address this question using a model multi-valent protein system consisting of repeats of Small Ubiquitin-like Modifier (SUMO) protein and a SUMO-interacting motif (SIM). These proteins undergo phase separation into liquid-like droplets. We combine microrheology and quantitative microscopy to determine affect of binding affinity on the viscosity, density and surface tension of these droplets. We also use fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS) and partitioning experiments to probe the structure and dynamics within these droplets. Our results shed light on how inter-molecular interactions manifests in droplet properties, and lay the groundwork for a comprehensive biophysical picture of intracellular RNA/protein organelles. [Preview Abstract] |
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P1.00216: Fluorescence microscopy techniques for characterizing the microscale mechanical response of entangled actin networks Savanna Blair, Tobias Falzone, Rae Robertson-Anderson Actin filaments are semiflexible polymers that display complex viscoelastic properties when entangled in networks. In order to characterize the molecular-level physical and mechanical properties of entangled actin networks it is important to know the in-network length distribution and the response of entangled filaments to local forcing. Here we describe two single-molecule microscopy protocols developed to investigate these properties. Using confocal fluorescence microscopy and ImageJ image analysis we have developed a protocol to accurately measure the in-network actin length distribution. To characterize the deformation of actin filaments in response to perturbation, we trap micron size beads embedded in the network with optical tweezers and propagate the beads through the entangled filaments while simultaneously recording images of fluorescent-labeled filaments in the network. A sparse number of labeled filaments dispersed throughout the network allow us to visualize the movement of individual filaments during perturbation. Analysis of images taken during forcing is carried out using a combination of vector mapping and skeletonization techniques to directly reveal the deformation and subsequent relaxation modes induced in entangled actin filaments by microscale strains. We also determine the dependence of deformation modes on the relative filament position relative to the strain. [Preview Abstract] |
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P1.00217: Assembly, Properties and Function of Synthetic Phase-Separated RNA/Protein Organelles Nicole Taylor, Shana Elbaum, Howard Stone, Clifford Brangwynne Non-membrane bound RNA/protein (RNP) bodies play a key role in cellular RNA processing steps. Many RNA helicases, required for RNA processing, are key components of RNPs. Consistent with this, a purified RNA helicase, Laf-1, exhibits a salt and protein concentration dependent phase separation \textit{in vitro}, resulting in liquid-like droplets. We use such \quad synthetic RNPs to study the biophysics of RNP assembly, and to elucidate the link between their physical properties and function. To accomplish this, we are developing custom microfluidic devices to measure biophysical properties, nucleation and growth kinetics, and RNA processing function of droplets. We measure droplet viscosity by applying a shear stress to protein droplets that adhere to the channel wall; measurements are consistent with those taken using a particle microrheology approach. We also monitor and control protein droplet nucleation using oil/water emulsions. Our results provide a new platform for addressing how the cell regulates organelle assembly and properties through protein, RNA, and ATP concentration. We anticipate that these findings will offer insight into the contribution of RNPs in key RNA processing functions in the cell. [Preview Abstract] |
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P1.00218: POLYMERS FOR SOLAR ENERGY |
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P1.00219: Design of block and graft copolymers for use as compatibilizers in organic solar cell active layers Dylan Kipp, Venkat Ganesan Recent experiments have suggested that the use of block and graft copolymer compatibilizers in polymer based donor-acceptor mixtures can improve both the morphology and thermal stability of organic solar cell active layers. Inspired by these successes, we use the framework of self consistent field theory to study the influence of copolymer compatibilizers on the interfacial properties of donor-acceptor blends. First, we calculate the reduction in the interfacial tension (and hence the driving force towards macrophase segregation) brought on by the copolymer compatibilizer as a function of the copolymer architecture. Second, we calculate the effective interaction between two copolymer monolayers at the interfaces between the donor and acceptor domains. The results of this second study allow us to comment on the expected ability of the copolymer compatibilizer to reduce the coalescence of domains. Overall, our results suggest important rules for designing copolymer compatibilizers to influence both kinetically-trapped and equilibrium morphologies of donor-acceptor blends. [Preview Abstract] |
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P1.00220: Self-Assembly of Carotenoids During Solution Casting of Solar Devices Dusantha Alwis, Dilru Ratnaweera, Thusitha Etampawala, Mark Dadmun, Udumalagala Chandrika, Pradeep Jayaweera Self assembly of carotenoids is a common phenomenon in nature and seems to be closely related to the functions of these natural dyes in solar devices. The large absorption coefficients in the visible region of carotenoids make them a well suited natural resource for dye-sensitized solar cells (DSSC). The performance of carotenoid based solar devices mainly depends on the photo-electrochemical properties of the active material (carotenoids) and their self-assembled morphology within solar devises. These associations of molecules will affect the light absorption, emission and energy harvesting abilities of these solar devices. Two types of highly conjugated natural carotenoids having mono and dicarboxy terminal groups, namely bixin and norbixin, were extracted from annatto seeds. In the current study, small angle neutron scattering experiments were carried out to examine the modes of assemblies of bixin and norbixin during solution processing of DSSCs. Spherical shape aggregates with rough interfaces were observed in acetone medium, which is a good solvent for hydrocarbon chain. The shape of the aggregates slightly deviates from spherical to slightly elongated shape at high volume fractions of carotenoids. Bixin and norbixin show different association behaviors as a function of their concentration. [Preview Abstract] |
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P1.00221: Hydrogen Bonding-mediated Conjugated Polymers for Bulk-Heterojunction Organic Photovoltaics Yen-Hao Lin, Wanyi Nie, Aditya Mohite, Gautam Gupta, Rafael Verduzco We use hydrogen bonding interactions to prevent large scale phase separation and improve polymer blend OPVs. Poly(3-hexylthiophene) (P3HT) donor polymer and poly(2,7-(9$\prime $,9$\prime $-dioctyl-fluorene)-alt-5,5-(4$\prime $,7$\prime $-di-2-thienyl-2$\prime $,1$\prime $,3$\prime $-benzothiadiazole) (PFTBT) acceptor polymer with self-associating, quadruple hydrogen bonding end groups (2-ureido-4[1H]-pyrimidinone, UPy) are used to explore the role of hydrogen bonding associations on blend morphology and photovoltaic performance. We study three systems: P3HT/PCBM, PFTBT/PCBM and P3HT/PFTBT and analyze by AFM, impedance, and device performance. In P3HT/PCBM, the performance is improved from 1.21{\%} to 2.16{\%} using UPy-terminated P3HT due to the enhanced long range order of semi-crystalline P3HT. In PFTBT/PCBM, the performance is decreased from 1.84{\%} to 1.08{\%} using UPy-terminated PFTBT due to entanglement of non-crystalline PFTBT chains. In P3HT/PFTBT system, the performance is improved from 0.43{\%} to 0.77{\%} with the use UPy-terminated P3HT and PFTBT because of suppressed macro-phase separation with maintained long range order of P3HT under annealing temperature. The impedance analysis under short circuit and illumination conditions indicates the faster charge transport and reduced charge recombination within the better performed devices. This study shows that the hydrogen bonding interactions can reduce phase separation but not produce better BHJ devices in all cases perhaps because some phase separation in blends is still required. [Preview Abstract] |
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P1.00222: Side Chain Engineering of Naphthalenediimide-Based N-type Polymer for High-Performance All-Polymer Solar Cell near 6{\%} Efficiency Changyeon Lee, Hyunbum Kang, Wonho Lee, Taesu Kim, Ki-Hyun Kim, Han Young Woo, Cheng Wang, Bumjoon Kim Despite the attractive features of all-polymer solar cells (all-PSCs), i.e., enhanced absorption coefficients, the tunability of their energetic and chemical properties and their thermal and mechanical stabilities, they still face the great challenge of having significantly low power conversion efficiency (PCE) values of only 3-5{\%}. The prominent origins of the poor efficiency of all-PSCs are the undesirable features of the bulk-heterojunction (BHJ) blend morphology including the phase-separated large-scale domain size, reduced ordering of the polymer chains. Tuning side alkyl chains of conjugated polymers is an effective route for manipulating the blend morphology in BHJ type solar cells. However, the role of side chains in all-PSCs is poorly understood. Herein, we report high-performing all-PSCs with 5.96{\%} efficiency by developing a series of naphthalenediimide (NDI)-based polymer acceptors with different alkyl side chains. We demonstrated that the use of the PNDIT with hexyldecyl side chains produced highly-ordered polymer stackings with strong face-on geometry and at the same time, forming the optimal BHJ morphology with finely separated phase domains, all of which contributed together to induce well-balanced $\mu $e/$\mu $h ratio and generate efficient all-PSCs with PCEs near 6{\%}. [Preview Abstract] |
(Author Not Attending)
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P1.00223: Fabrication of Organic Bulk Heterojunction Solar Cells on Flexible Substrates Gabriel Calderon, Milzaida Merced-Sanabria, Carolyn Carradero-Santiago, Josee Vedrine-Paul\'eus The active layer for the organic solar cells fabricated is composed of P3HT:PCBM, poly(3-hexylthiophene) (P3HT) as electron donor and phenyl-C61-butyric acid methyl ester(PCBM) as electron acceptor. These polymers were used due to their promising characteristics for devices such as bulk heterojunction solar devices. We used polyethylene terephthalate (PET) substrates, a highly flexible plastic, with indium tin oxide (ITO) as the transparent conducting anode for the device, and UV lithography technique to pattern the ITO; this is to facilitate multiple devices on a single substrate. The fabrication process for pattern transfer incorporates developing and etching processes. We diluted the HCl and DI water to etch out the ITO. PEDOT:PSS and active layer of P3HT:PCBM were deposited on (3.0 sq-cm) patterned of ITO/PET by spin coating method. The cathode was thermally evaporated with Al. We characterized the device using a sourcemeter. We also simulated portions of the device using PET on graphene as the substrate. [Preview Abstract] |
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P1.00224: ORGANIC ELECTRONICS AND PHOTONICS |
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P1.00225: Electrochemiluminescent Ion Gels for DC-Driven, Sub-2V Solid-State Emissive Devices by Incorporating Redox Coreactants Hong Chul Moon, Timothy P. Lodge, C. Daniel Frisbie We have demonstrated a solid-state DC-driven electrochemiluminescent (ECL) device using a solution processable, emissive ECL gel based on polystyrene-block-poly(methyl methacrylate)-block-polystyrene (SMS) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). Tetrabutylammonium oxalate (TBAOX) was incorporated into the ECL gel for a coreactant strategy. Oxalate can be viewed as a consumable fuel for the device providing reducing power and cutting the overall operating voltage. The device was fabricated by a simple two-step solution process. Application of 1.6 V DC bias across the device resulted in the onset of light emission. The maximum luminance was achieved at 1:5 mole ratio of ECL luminophore (Ru(bpy)$_{\mathrm{3}}$(PF$_{\mathrm{6}})_{\mathrm{2}})$ and TBAOX, and the turn-on voltage was independent of the composition. The simplicity of the ECL device and its low voltage operation characteristics make it potentially attractive as a display element for printed electronics. [Preview Abstract] |
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P1.00226: Ferroelectric switching behavior in morphology controlled ferroelectric-semiconductor polymer blends for organic memory Eunhee Lim, Gregory Su, Edward Kramer, Michael Chabinyc Memory is a fundamental component of all modern electronic systems. Organic ferroelectric memories are advantageous because they are thin and lightweight devices that can be made printable, foldable, and stretchable. Organic ferroelectric memories comprise a physical blend of an organic semiconducting polymer and an insulating ferroelectric polymer as the active layer in a thin film diode. Controlling the thin film morphology in these blends is important for electrical properties of the resulting device. We have found that when a semiconducting thiophene polymer with polar alkanoate side chains (P3EPT) is blended with well-studied ferroelectric polymer poly [(vinylidenefluoride-co-trifluoroethylene] P (VDF-TrFE), the resulting film has low surface roughness and more controllable domain sizes compared to the widely used poly (3-hexylthiophene). This difference allows more reliable study of the ferroelectric switching behavior in devices with domain size of about 100nm. The influence of the 3D composition measured by a combination of methods, including soft x-ray microscopy, on the electrical characteristics will be presented. [Preview Abstract] |
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P1.00227: Microscopic simulations of electronic excitations in donor-acceptor heterojunctions of small-molecule based solar cells Bjoern Baumeier Fundamental processes involving electronic excitations govern the functionality of molecular materials in which the dynamics of excitons and charges is determined by an interplay of molecular electronic structure and morphological order. To understand, e.g., charge separation and recombination at donor-acceptor heterojunctions in organic solar cells, knowledge about the microscopic details influencing these dynamics in the bulk and across the interface is required. For a set of prototypical heterojunctions of small-molecule donor materials with C$_{60}$, we employ a hybrid QM/MM approach\footnote{JCTC \textbf{7}, 3335 (2011)} linking density-functional and many-body Green's functions theory\footnote{JCTC \textbf{8}, 2790 (2012)} (DFT/GW-BSE) to polarizable force-fields\footnote{JCTC \textbf{10}, 3140 (2014)} and analyze the charged and neutral electronic excitations therein. We pay special attention the spatially-resolved electron/hole transport levels, as well as the relative energies of Frenkel and charge-transfer excitations at the interface. Finally, we link the molecular architecture of the donor material, its orientation on the fullerene substrate as well as mesoscale order\footnote{Nat. Mater., \textbf{in print} (2014)} to the solar cell performance. [Preview Abstract] |
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P1.00228: Enhancing the Thermoelectric Characteristics of PEDOT:PSS Through the Incorporation of a Redox-Active Small Molecule Edward Tomlinson, Matthew Willmore, Xiaoqin Zhu, Bryan Boudouris The polymer blend composed of poly(3,4-ethylene dioxythiophene) and poly(styrene sulfonate) (PEDOT:PSS) is a leading organic thermoelectric material due to its high-performing properties. Here, we establish the effect of incorporating the redox-active small molecule\textbf{ }4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH) on the structural and thermoelectric properties of PEDOT:PSS. Specifically, the thermoelectric power factor (PF) was monitored as a function of TEMPO-OH loading, elucidating a clear trend in the PF. Importantly, at loadings as low as 5{\%} TEMPO-OH, by mass, the thermopower of the sample was increased by a factor of two. Furthermore, the role of the TEMPO-OH on the thin film morphology of the composite material is examined through the use of grazing incidence-wide angle x-ray scattering (GI-WAXS) and atomic force microscopy (AFM). Despite the acidic conditions associated with the presence of PSS, the existence of radical functionality is confirmed through electron paramagnetic resonance (EPR) spectroscopy. Through careful tuning, the optimized conditions outlined within this work results in PF gains in excess of 40{\%}. [Preview Abstract] |
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P1.00229: Morphology optimization for enhanced performance in organic photovoltaics Olga Wodo, Jaroslaw Zola, Baskar Ganapathysubramanian Organic solar cells have the potential for widespread usage due to their low cost-per-watt and mechanical flexibility. Their wide spread use, however, is bottlenecked primarily by their low solar efficiencies. Experimental evidence suggests that a key property determining the solar efficiency of such devices is the final morphological distribution of the electron-donor and electron-acceptor constituents. By carefully designing the morphology of the device, one could potentially significantly enhance their performance. This is an area of intense experimental effort that is mostly trial-and-error based, and serves as a fertile area for introducing mechanics and computational thinking. In this work, we use optimization techniques coupled with computational modeling to identify the optimal structures for high efficiency solar cells. In particular, we use adaptive population-based incremental learning method linked to graph-based surrogate model to evaluate properties for given structure. We study several different criterions and find optimal structure that that improve the performance of currently hypothesized optimal structures by 29{\%}. [Preview Abstract] |
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P1.00230: Facile Control of a Wide Range of Regioregularity: Significant Influence on Mechanical and Electrical Properties of Conjugated Polymers Jin-Seong Kim, Jae-Han Kim, Wonho Lee, Hojeong Yu, Hyeong Jun Kim, Inho Song, Joon Hak Oh, Taek-Soo Kim, Bumjoon Kim While regioregularity (RR) has been known to have a strong influence on inherent properties of conjugated polymer, systematic study of RR has been limited due to the lack of synthetic methodology. Herein, we prepared a series of poly(3-hexypthiophenes) (P3HTs) having a wide range of RR from 64 to 98{\%} by the modified Grignard metathesis method that utilizes the dimer moiety. We observed that the RR determines crystalline behavior, mechanical and electrical properties of P3HT. Although higher RR P3HT had higher hole mobility, its increased degree of crystallinity induced fragile nature of polymers (elongation break \textless 1{\%}). In contrast, lower RR had lower elastic modulus and thereby leading to significant reduction of fragility. Therefore, our finding suggested that the control of RR is critical to regulate the properties of conjugated polymers between electrical performance and mechanical resilience as depending on the purpose of the applications. (i.e flexible portable devices vs high performance panel) [Preview Abstract] |
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P1.00231: Using COMSOL Multiphysics Software to Analyze the Thin Film Resistance Model of a Conductor on PET Carolyn Carradero-Santiago, Milzaida Merced-Sanabria, Josee Vedrine-Paul\'eus In this research work, we will develop a virtual model to analyze the electrical conductivity of a thin film with three layers, one of graphene or conducting metal film, polyethylene terephthalate (PET) and Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS). COMSOL Multiphysics will be the software use to develop the virtual model to analyze the thin-film layers. COMSOL software allows simulation and modelling of physical phenomena represented by differential equations such as that of heat transfer, fluid movement, electromagnetism and structural mechanics. In the work, we will define the geometry of the model; in this case we want three layers-PET, the conducting layer and PEDOT:PSS. We will then add the materials and assign PET as the lower layer, the above conductor as the middle layer and the PEDOT:PSS as the upper layer. We will analyze the model with varying thickness of the top conducting layer. This simulation will allow us to analyze the electrical conductivity, and visualize the model with varying voltage potential, or bias across the plates. [Preview Abstract] |
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P1.00232: Study of biodegradable polymers for ``green'' devices Carlos Perez, Xiaomei Jiang $\Pi -$conjugated polymers such as polythiophenes are conventional picks for cost-effective organic solar cells. However, these organic semiconductors are not environment-friendly since the polymer back bones require temperature higher than 300$^{\mathrm{0}}$C to be decomposed, thus will cause potential environment problems upon disposal. In this work, the optical and electronic properties of biodegradable polymers, conjugated poly(disulfidediamine), were examined via continuous wave laser spectroscopy, FTIR spectroscopy and conductivity measurement. We found that the attachment of a side chain to aromatic ring increases both photo and thermal stability, as well as higher conductivity. Thermal annealing improved the film morphological, photophysical and electronic properties. Photo-Induced Absorption (PIA) reveals different features comparing with conventional pi-conjugated polymers. No observation of long-lived photoexcitations such as polarons or triplets which are common with pi-conjugated polymers. Instead, we found the formation of low energy species upon thermal annealing in these biodegradable polymers. [Preview Abstract] |
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P1.00233: Electron transport and light absorption/emission in molecular complexes Miguel Martinez, Lev Mourokh In this work, we address photon-assisted electron transport in molecular triads and tetrads connected to the leads. Donor-bridge-acceptor triads are promising candidates for efficient organic solar cells, as the photon absorption makes it possible to transfer electrons against the applied voltage. Deriving and solving numerically the equations of motion for electron creation/annihilation operators, we obtain the parameters of molecular complexes which are optimal for a maximal efficiency of the light harvesting. For donor-bridge-bridge-acceptor tetrads, we determine the conditions for another phenomenon, {\it optical up-conversion}. Electron transport along the applied voltage and the photon absorption at one of the bridges facilitates the photon emission at another bridge with higher frequency. Using the same equations of motion approach, we obtain the emitted electromagnetic energy and its dependence on the system parameters. [Preview Abstract] |
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P1.00234: Nanostructural Patterning Improves the Performance of Non-volatile Polymer Memory Devices Seung Hyun Sung, Bryan W. Boudouris Organic nonvolatile memory devices based on polymer ferroelectric materials are a promising approach toward the development of low-cost memory due to the ease of processing and flexibility associated with the device. Here, we focus on a memory device with a two-component active layer and a diode structure. This ferroelectric diode (FeD) has a nanostructured active layer, composed of ferroelectric and semiconducting polymers, and it can provide easy access to high-performance polymer-based memory devices. In order to create these nanostructured active layers, we have utilized electron beam (e-beam) lithography for the simple fabrication of a desired pattern on the ferroelectric polymer layer. Then, a semiconducting polymer was deposited into the nanoporous ferroelectric layer to complete the ordered heterojunction. By optimizing the nanostructure, the memory retention and ON/OFF current density ratio performance of FeD is greatly enhanced ($e.g.,$ the ON/OFF ratio is a factor of 3 greater) over a traditional blended diode. This ability to control the ferroelectric polymer morphology will open new fields of evaluating in the relationships between structure and performance in organic memory devices. [Preview Abstract] |
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P1.00235: Cross-linking high-k fluoropolymer gate dielectrics enhances the charge mobility in rubrene field effect transistors Jwala Adhikari, Matthew Gadinski, Qing Wang, Enrique Gomez Polymer dielectrics are promising materials where the chemical flexibility enables gate insulators with desired properties. For example, polar groups can be introduced to enhance the dielectric constant, although fluctuations in chain conformations at the semiconductor-dielectric interface can introduce energetic disorder and limit charge mobilities in thin-film transistors. Here, we demonstrate a photopatternable high-K fluoropolymer, poly(vinylidene fluoride-bromotrifluoroethylene) P(VDF-BTFE), with a dielectric constant between 8 and 11. The bromotrifluoroethylene moiety enables photo-crosslinking and stabilization of gate insulator films while also significantly enhancing the population of trans torsional conformations of the chains. Using rubrene single crystals as the active layer, charge mobilities exceeding 10 cm$^{2}$/Vs are achieved in thin film transistors with cross-linked P(VDF-BTFE) gate dielectrics. We hypothesize that crosslinking reduces energetic disorder at the dielectric-semiconductor interface by suppressing segmental motion and controlling chain conformations of P(VDF-BTFE), thereby leading to approximately a three-fold enhancement in the charge mobility of rubrene thin-film transistors over devices incorporating uncross-linked dielectrics or silicon oxide. [Preview Abstract] |
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P1.00236: Monte Carlo simulations of charge transport in heterogeneous organic semiconductors Pyie Phyo Aung, Kiran Khanal, Jutta Luettmer-Strathmann The efficiency of organic solar cells depends on the morphology and electronic properties of the active layer. Research teams have been experimenting with different conducting materials to achieve more efficient solar panels. In this work, we perform Monte Carlo simulations to study charge transport in heterogeneous materials. We have developed a coarse-grained lattice model of polymeric photovoltaics and use it to generate active layers with ordered and disordered regions. We determine carrier mobilities for a range of conditions to investigate the effect of the morphology on charge transport. [Preview Abstract] |
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P1.00237: ABSTRACT WITHDRAWN |
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P1.00238: ABSTRACT WITHDRAWN |
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P1.00239: ABSTRACT WITHDRAWN |
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P1.00240: The impact of P3HT molecular weight and solvent composition on P3HT films processed from binary solvent mixtures Lawson LLoyd, Madeleine Gordon, David Boucher Recent experimental endeavors have shown that well-ordered P3HT assemblies formed in solution can improve the crystallinity and morphological uniformity of thin films and composites, thereby providing a promising new route to more efficient polymeric optoelectronic materials. We have studied the assembly and crystallinity of two regioregular poly(3-hexylthiophene) (P3HT) samples, M$_{\mathrm{n}} \approx $ 28 kDa and M$_{\mathrm{n}}$ $\approx $ 65 kDa, in several different binary mixtures of organic solvents. We use an excitonic coupling analysis of the UV/Vis absorbance spectra to assess the impact that the solvent and the molecular weight of P3HT have on the relative structural order of the polymer assemblies. In addition, we investigate the influence that the solvent composition and the structural order of P3HT aggregates have on the assembly and organization of P3HT films. We use optical and atomic force microscopy techniques to study thin films of P3HT processed from different solvent mixtures. Our results show that relatively small variations to the P3HT solutions can produce significant changes in the morphology and macromolecular structures of the P3HT films. [Preview Abstract] |
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P1.00241: POLYMERS IN BATTERIES AND ELECTROCHEMICAL CAPACITORS |
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P1.00242: In situ Mechanistic Investigation of an Organic Radical Polymer Cathode on Interfacial Charge Transport and Cycling Stability Fei Li, Jodie Lutkenhaus Organic radical polymers have gained increased attention as cathodes for organic radical batteries due to their fast charge transport and high cycling stability. These features make them a promising alternative to conventional lithium-ion batteries. One polymer of interest is a nitroxide radical polymer, poly(2,2,6,6-tetramethylpiperidinyloxymethacrylate) (PTMA), which is capable of a two-electron transfer process. The specific capacity of PTMA as cathode has a reported value between 77 to 220 mAh/g, depending on the charge/discharge conditions. Most work with PTMA has largely emphasized electrode optimization to improve its capacity by adding highly conductive materials or by designing new forms of radical polymers. There is little molecular level detail on the charge storage process and electrode/electrolyte interfacial activities in such systems. Here, we present the application of in situ characterization techniques towards the charge storage process in PTMA. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) monitors various electrode physical properties (e.g. mass, shear viscosity) during controlled electrochemical interrogation (cyclic voltammetry, charge discharge). Electrochemical impedance spectroscopy probes various charge storage and transport events at a range of frequencies and potentials. With this information attained, a clearer picture of charge storage in organic radical battery cathodes can be formed. [Preview Abstract] |
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P1.00243: Flexible Hybrid Electrodes Containing Vanadium Pentoxide (V$_{2}$O$_{5})$ and an Electron- and Ion-Conducting Diblock Copolymer for Energy Storage Hyosung An, Jared Mike, Kendall Smith, Lisa Swank, Yen-Hao Lin, Stacy Pesek, Rafael Verduzco, Jodie Lutkenhaus Vanadium pentoxide (V$_{2}$O$_{5}$) is a promising cathode material for Lithium-ion batteries due to its high capacity, high energy density, and cost-effectiveness. However, its low lithium-ion diffusion coefficient (10$^{-12}$ - 10$^{-13}$ cm$^{2}$/s), low electronic conductivity (10$^{-2}$ - 10$^{-3}$ S/cm), and severe volumetric changes during cycling have hindered its application in practical devices. One way to address these problems is to design hybrid electrodes that incorporate a second active material. For this purpose, poly(3-hexylthiophene)-\textit{block}-poly(ethylene oxide) (P3HT-$b$-PEO) block copolymer containing electron- and ion-conducting polymer blocks was introduced to a V$_{2}$O$_{5}$ electrode system. Cathodes are prepared by mixing aqueous dispersions of block copolymer, V$_{2}$O$_{5}$, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and drop casting. The V$_{2}$O$_{5}$ and P3HT-$b$-PEO hybrid electrode showed synergistic results, having improved electrochemical storage performance and mechanical property. We also demonstrated a flexible battery prototype using the P3HT-$b$-PEO/V$_{2}$O$_{5}$ cathode. [Preview Abstract] |
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P1.00244: Phase Behavior and Electrochemical Performance of Solid-State Magnesium Ion Electrolytes from Diblock Copolymers Jacob Thelen, Sebnem Inceoglu, Nitash Balsara Batteries utilizing magnesium metal anodes are considered a promising candidate for the next generation of energy storage with performance beyond lithium ion technology. The development of a safe, stable magnesium ion-conducting electrolyte represents one of the major barriers to the advancement of magnesium battery technology. One approach to increasing the safety and stability of electrolytes is to replace flammable organic solvents with more stable polymeric species. We report on the phase behavior and electrochemical performance of solid-state magnesium ion electrolytes derived from diblock copolymers. [Preview Abstract] |
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P1.00245: Polyhedral Oligomeric Silsesquioxanes -- Based Hybrid Electrolytes with Controlled Network Structure Qiwei Pan, Christopher Li High ion conductivity and mechanical integrity are the most important properties in the application of solid polymer electrolytes (SPEs). We herein report synthesis and characterization of hybrid electrolytes with inorganic polyhedral oligomeric silsesquioxanes (POSS) as the crosslinker. The SPEs were prepared by a facile one-pot reactions between octakis[3-(glycidyloxy)propyldimethylsiloxy]silsesquioxane and bis(3-aminopropyl) terminated poly(ethylene glycol) (PEG) in the present of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). Uniform distribution of POSS and LiTFSI in the SPEs were confirmed by SEM-BSD and SEM-EDX. We show that both ionic conductivity and mechanical properties of the SPE can be easily tuned by varying POSS contents. Correlation between the SPE network structure and the ionic conductivity and mechanical properties will be discussed. [Preview Abstract] |
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P1.00246: HIERARCHICAL ASSEMBLY OF BLOCK COPOLYMERS AND SOFT NANOPARRTICLES IN SOLUTIONS. |
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P1.00247: Structure and Ionic Conductivity Evolution of a Block Copolymer Electrolyte during Thermal Annealing Mahati Chintapalli, Nitash Balsara Mixtures of block copolymers (BCPs) and lithium salts are promising materials for battery electrolytes because they exhibit high ionic conductivity and high modulus. However, since most polymer electrolytes show high conductivities only at temperatures above ambient, it is important to understand how the structure and ionic conductivity of BCP electrolytes evolve during thermal annealing. \textit{In situ s}mall angle X-ray scattering and ac impedance spectroscopy were used to characterize a BCP electrolyte, lamellar polystyrene-\textit{block}-poly(ethylene oxide) mixed with lithium bis( trifluoromethanesulfonylimide) (LiTFSI), during thermal annealing. As annealing progressed, long range lamellar order and domain spacing increased, and scattering contrast between the two BCP phases decreased. A concomitant decrease in ionic conductivity was observed. [Preview Abstract] |
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P1.00248: $\beta -$NMR Measurements of Lithium Ion Transport in Thin Films of Pure and Lithium-Salt-Doped Poly(ethylene oxide) Iain McKenzie, Masashi Harada, David L. Cortie, Robert F. Kiefl, C.D. Philip Levy, W. Andrew MacFarlane, Ryan M.L. McFadden, Gerald D. Morris, Shin-Ichi Ogata, Matthew R. Pearson, Jun Sugiyama $\beta -$Detected nuclear spin relaxation of $^{8}$Li$^{+}$ has been used to study the microscopic diffusion of lithium ions in thin films of poly(ethylene oxide) (PEO), PEO with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), PEO with lithium triflate (LiTf) and PEO with lithium trifluoroacetic acid (LiTFA) with monomer-to-salt ratios of 8.3:1. Hopping of Li$+$ above $\sim$ 250 K follows an Arrhenius law in all of the films. Diffusion of Li$^{+}$ is fastest in pure PEO and decreases in order LiTFSI \textgreater LiTf \textgreater LiTFA. We observed the activation energy for hopping ($E_{\mathrm{A}})$ and the intrinsic hop rate ($\tau _{0}^{-1})$ both increasing in order LiTFA \textless LiTf \textless LiTFSI \textless PEO but the larger $\tau _{0}^{-1}$ outweighs the larger $E_{\mathrm{A}}$ and results in Li$^{+}$ motion being fastest in the pure polymer. The results will be discussed in terms of the ionicity of the salt. [Preview Abstract] |
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P1.00249: Increase of the Effective Dispersity in ARB-Type Triblock Copolymer Sanghoon Woo, Hyunjung Jung, June Huh, Du Yeol Ryu, Joona Bang The domain spacing of block copolymer (BCP) has been mainly controlled by molecular weight and block immiscibility. Instead of these traditional variables, we designed a new type of BCP, namely ARB type triBCP, where the R represents the short middle block composed of A and B random copolymer. It was expected that the R block provide the effect of increased ``effective'' dispersity via compositional distribution, leading to an increased domain size compared to the AB diBCP with same MW and dispersity. We prepared various ARB type triBCPs and AB diBCPs having the similar dispersity via living-radical polymerization, and their morphologies were characterized by TEM, SAXS, and GISAXS. As a result, it was shown that the ARB-type triBCP exhibited a significant increase in the domain spacing compared to the AB diBCPs with same MW and dispersity. These results were also compared with theoretical viewpoint. [Preview Abstract] |
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P1.00250: Control Large Nanoparticle Assemblies in Suparmolecular Nanoparticle Thin Films Jingyu Huang, Ting Xu Nanocomposites can generate new properties beyond those offered by organic and inorganic building blocks to meet the demands in functional materials. The collective properties of nanocomposite materials depend on both the nature of individual building block and their spatial arrangements. With the recent development, colloidal synthesis and surface modification methods provide inorganic nanoparticles (NPs) with various sizes, shapes, compositions and properties in a facile manner. Block copolymer-based supramolecules further provide more versatile routes to control spatial arrangement of the nanoparticles over multiple length scales. Nanoparticle size is a critical parameter determining the optical and electronic properties. However, most of studies to date focused on nanoparticle smaller than 10 nm in size. Here, our recent studies showed that the assembly of nanoparticles with size larger than 10 nm can be achieved in the supramolecular nanocomposite thin films by finely tuning the ligand-polymer interactions and the sample treatment conditions. Both the overall morphology of the nanoparticle assemblies and inter-particle distances can be readily tailored. These new results opened a viable approach to construct functional materials using nanoparticles with different quantum confinement effects. [Preview Abstract] |
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P1.00251: Crystallization Driven Responsive Janus Assembly Hao Qi, Shan Mei, Christopher Li Responsive and dynamic nanostructures are ubiquitous in Nature, and they are also utter importance for applications such as sensing and drug delivery. Herein we report a series of hierarchical block copolymer nanostructure that is able to undergo 2D (sheet-like) to 3D (bowl-like) shape changing upon specific external stimuli. Freestanding Janus nanosheets were prepared via crystallization-driven self-assembly of poly($\varepsilon $-caprolactone)-b-poly(acrylic acid) (PCL-b-PAA) and subsequent crosslinking and disassembly process. Due to the mechanical contrast between the two layers, and the chemical responsiveness of the PAA layer, such Janus nanosheets transform a mechanically stable nanobowl upon pH change. Atomic force microscopy and transmission electron microscopy results confirmed the Janus structure and bending behavior. Detailed structural characterization and shape changing mechanisms will be discussed. [Preview Abstract] |
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P1.00252: Meso-scale Modeling of Self-assembly of Polymer-Grafted Nanoparticles Derrick Mancini, Sanket Deshmukh, Subramanian Sankaranarayanan We develop meso-scale models to explore the self-assembly behavior of polymer-grafted nanoparticles. Specifically, we study nanoparticles with grafts of the thermo-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM), which undergoes a coil-to-globule transition across the LCST at around 305 K. The atomic-scale mechanism of the coil-to-globule transition of polymers grafted nanoparticles and their interactions (agglomeration, assembly behavior) with other particles that are in its vicinity is poorly understood, yet knowledge about these interactions would enable designing novel self-assembled materials with well-defined structural and dynamical properties. Additionally, the effects of chemical nature, geometry, and morphology of the nanoparticle surface on the conformational transition of thermo-sensitive polymers is also unknown. We report on 1) development of all-atom models of polymer-grafted nanoparticles to conduct MD simulations at atomic-levels and 2) perform mesoscopic scaling of the conformational dynamics resulting from the atomistic simulations with the aid of coarse-grained or meso-scale models of PNIPAM and its composites. Coarse-grained simulations allow modeling of larger assemblies of polymer-grafted nanoparticles over longer time scales. [Preview Abstract] |
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P1.00253: Mesoscale Polymer Assemblies Satyan Choudhary, Jonathan Pham, Alfred Crosby Materials encompassing structural hierarchy and multi-functionality allow for remarkable physical properties across different length scales. Mesoscale Polymer (MSP) assemblies provide a critical link, from nanometer to centimeter scales, in the definition of such hierarchical structures. Recent focus has been on exploiting these MSP assemblies for optical, electronic, photonics and biological applications. We demonstrate a novel fabrication method for MSP assemblies. Current fabrication methods restrict the length scale and volume of such assemblies. A new method developed uses a simple piezo-actuated motion for de-pinning of a polymer solution trapped by capillary forces between a flexible blade and a rigid substrate. The advantages of new method include ability to make MSP of monodisperse length and to fabricate sufficient volumes of MSP to study their physical properties and functionality in liquid dispersions. We demonstrate the application of MSP as filler for soft materials, providing rheological studies of the MSP with surrounding matrices. [Preview Abstract] |
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P1.00254: SURFACES INTERFACES AND POLYMERIC THIN FILMS |
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P1.00255: Structure of polymer brushes on flat substrates and its dependence on the conditions of the surface-initiated polymerization Rohan Patil, Jiri Srogl, Douglas Kiserow, Jan Genzer We demonstrate an efficient method of degrafting surface anchored poly(methyl methacrylate) brushes using tetra butyl ammonium fluoride (TBAF). The grafted polymers are grown using standard atom transfer radical polymerization method which provides good control by varying the catalyst ratio (Cu$^{\mathrm{(II)}}$:Cu$^{\mathrm{(I)}})$. The sample surface has been characterized before and after degrafting by means of X-ray photoelectron spectroscopy, ellipsometry, and time-of-flight secondary ion mass spectrometry. The degrafted polymer has been characterized using highly sensitive size exclusion chromatography, which provided information about the complete molecular weight distribution. The grafting density of PMMA chains is calculated as 0.517 chains/nm$^{2}$. The study of the dependence of the grafting density on the ATRP inhibitor/catalyst ratio evidences to an effect of early termination of the growing chains when a lower control on the polymerization step is exercised. Control of the degrafting process is provided by tuning time, temperature, concentration of the TBAF, which - in conjunction with spatial control - allows for the creation of polymer brush patterns and surface gradients. [Preview Abstract] |
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P1.00256: Tribological properties of adsorbed PEO nanolayers on planar solids Wenduo Zeng, Naisheng Jiang, Jake Lindberg, Maya K. Endoh, Tadanori Koga We report tribological properties of irreversibly adsorbed poly(ethylene-oxide) (PEO) nanolayers onto planar Si substrates. The adsorbed nanolayers ($\sim$ 3 nm in thickness) were derived from spin-cast polymer thin films ($\sim$ 50 nm in thickness) via thermal annealing and subsequent solvent leaching with water. We characterized the formation process of the adsorbed nanolayers and the detailed surface/film structures by using x-ray reflectivity, grazing incidence x-ray diffraction, and atomic force microscopy. In addition, the contact angle and adhesive property of the adsorbed layers were characterized. We will discuss the structure-property relationship of the adsorbed nanolayers. [Preview Abstract] |
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P1.00257: Effects of the Adsorbed Polymer Nanolayers on the Dewetting of Polystyrene Thin Films Justin Cheung, Jiaxun Wang, Naisheng Jiang, Maya Endoh, Tadanori Koga It was previously reported that irreversibly adsorbed polymer nanolayers can be produced on solid substrates by thermal annealing. This study sought to determine the impact of the adsorbed nanolayers on film stability of ultrathin polystyrene (PS) films. A series of bilayers composed of the bottom PS adsorbed nanolayers and PS overlayers with different molecular weights were prepared as model systems. The surface structures of the bilayer films annealed above the bulk glass transition temperature were analyzed by using optical and atomic force microscopes. We will discuss the unique roles of the adsorbed polymer chains in the stability of the liquid thin films. [Preview Abstract] |
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P1.00258: Coatings with Thermally Switchable Surface Energy Produced From Block Copolymer Films Raleigh Davis, Richard Register Polymer-based coatings are employed across a wide array of sectors. One application of such coatings is to impart a prescribed surface energy, $i.e.$ hydrophilic or hydrophobic character. The present work explores an approach to create surfaces with thermally switchable wetting behavior by employing coatings based on block copolymers which possess both hydrophilic and hydrophobic segments. The amphiphilic block copolymers were synthesized by coupling allyl-ended poly(ethylene oxide) (PEO) and hydride-ended poly(dimethylsiloxane) (PDMS) oligomers via a Pt catalyst. One PEO-PDMS diblock possessed an order-disorder-transition-temperature (T$_{ODT})$ of 64$^{\circ}$C as characterized by small angle x-ray scattering. Above the T$_{ODT}$ the polymer is a disordered melt, but below this temperature it self-assembles into alternating lamellae with a repeat spacing of 7.7 nm. When cooled through the T$_{ODT}$ in vacuum or dry air, the PDMS-enriched domains wet the film's surface, producing a hydrophobic surface with a contact angle (CA) $\approx $ 90$^{\circ}$ as measured from CA goniometry. However, when cooled under water or in humid air, a PEO-rich hydrophilic surface is produced, yielding CAs ranging from 20-40$^{\circ}$. The coatings can then be reversibly switched between the two states by reheating above the T$_{ODT}$, exposing to the appropriate environment, and re-cooling, ideally ``locking in'' the structure until the next processing cycle. The T$_{ODT}$, and thus the switching temperature, can be continuously tuned by blending with PEO-PDMS diblocks of different molecular weights. [Preview Abstract] |
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P1.00259: Potential Energy Calculations for Water Adsorption on Poly (methyl methacrylate) Mateusz J. Zuba, Patrick Howard, Brian Familo, Thorin Kane, Ross L. Netusil, Carolina C. Ilie The generosity of the NOYCE Research Grant enabled me to focus on the study of various polymers. The main goal was to study the molecular orbitals of poly (methyl methacrylate) (PMMA) and calculate the energy band gap. We also performed the potential energy calculations for our system: two polymer chains and water molecules. We obtained the activation energy from thermal desorption spectra of water on poly (methyl methacrylate) by employing Arrhenius analysis. [Preview Abstract] |
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P1.00260: Macroion Interaction at Polyelectrolyte Brush Interfaces Chen Qu The effect of macroions, including synthetic polyelectrolytes, DNA and proteins, on the structure and surface properties of charged polymer thin films remains inadequately understood partially due to the complexity involving the hydrophobic effect and the conformational change of polymeric macroions. In this work, we explore a group of inorganic nanocluster based macroions, hydrophilic polyoxometalates (POMs) of robust nanocluster structure and carrying high surface charges ($\sim$ 2-42 negative charges) to investigate their interaction with surface tethered poly-2-vinylpyridine (P2VP) brush-like thin films immersed in aqueous solution. We observe the collapse of swollen P2VP chains by adding POM macroions of increased concentration by AFM, QCM and contact goniometer measurements, in sharp contrast to the increased chain stretching by adding monovalent salts. A careful comparison is made between distinct POMs based on their charge, size and chemical nature. These findings serve as a good reference for theoretical model modification and design of new mesoporous composite membranes. [Preview Abstract] |
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P1.00261: Elastocapillarity: Adhesion and Wetting in Soft Polymeric Systems Zhen Cao, Mark Stevens, Andrey Dobrynin We study interactions of nanoparticles with adhesive elastic substrates by using molecular dynamics simulations and theoretical calculations. The deformation of nanoparticles and substrates are obtained as a function of the nanoparticle and substrate shear modulus, nanoparticle size, and strength of interactions. There are two different interaction regimes between nanoparticles and substrates. The classical JKR model can be applied to describe adhesion of strongly cross-linked large nanoparticles on rigid substrates when small nanoparticle deformations and substrate indentations take place. In this adhesion regime the deformation of nanoparticles and substrates is determined by balancing the elastic energy of deformation and the work of adhesion between a nanoparticle and a substrate. However, for the weekly cross-linked (soft) systems, the change of the surface energy of nanoparticle and substrate could play an important role in controlling nanoparticle-substrate interactions. In this so-called wetting regime the interaction between nanoparticle and substrate is determined by the surface tension of substrate or nanoparticle and the work of adhesion. We developed an analytical model describing crossover between adhesion and wetting regimes. In the framework of this model a crossover between different interaction regimes is controlled by a universal dimensionless parameter. [Preview Abstract] |
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P1.00262: ABSTRACT MOVED TO V1.00023 |
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P1.00263: Understanding ``grafting through'' polymerization reactions involving surface-bound monomers Preeta Datta, Jan Genzer ``Grafting through'' polymerization is based on a bulk radical polymerization reaction utilizing a self-assembled monolayer that contain polymerizable units. Free polymer chains formed in solution can incorporate the surface-bound monomers, and thereby, get covalently bonded to the surface. As more growing chains attach to the surface-bound monomers, an immobilized polymer layer is formed on the surface. We use a combination of computer simulation and experiments to comprehend this process. Specifically, we report on the effect of spatial density of the surface-monomers on the formation of the surface-bound polymers. We use a lattice-based bond fluctuation model with periodic boundary conditions to simulate such systems. For experimental validation, we create gradients of density of methacrylate units on flat Si wafers using silane chemistry. The proximity of the surface-bound polymerizable units promotes the ``grafting through'' process but prevents more free growing chains to ``graft to'' the polymerizable units. Our studies indicate that these two counter-active effects balance each other and do not affect the overall density of the surface-bound polymer layer, except in case of the highest theoretical packing density of surface-bound monomers. [Preview Abstract] |
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P1.00264: Effect of Interfaces on Self-diffusion and Glass Transition Temperature of Poly(isobutyl methacrylate) Thin Films Reika Katsumata, Austin Dulaney, Christopher Ellison In thin films, physical properties such as the glass transition temperature (Tg), modulus, and viscosity, are different compared to that in thick films due to higher interfacial area to volume ratio. However, the effects of film thickness and associated interfaces on self-diffusion are not well understood, partly because only a few techniques are available for such studies. In this study, we employed fluorescence recovery after patterned photobleaching to evaluate the self-diffusion coefficient (D) of fluorescently labeled poly(isobutyl methacrylate) (PiBMA, Mn $=$ 11 kg/mol, PDI $=$ 1.2). Films 16 - 300 nm in thickness were spin coated onto two substrates then D and Tg were examined: one set of films possessing attractive polymer/substrate interactions on silica substrates, and the other set possessing repulsive polymer/substrate interactions using poly(cyclohexylethylene) substrates. D was measured in the melt state (Tg $+$ 48 K) and the D of thick films were identical to the bulk value regardless of the substrate type. The D of a $\sim$ 19 nm thick film on a repulsive substrate was four times larger than its bulk value while Tg was increased by about 10-15 K. In contrast, attractive substrates typically do not affect D or Tg of PiBMA. [Preview Abstract] |
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P1.00265: Programming Surface Energy Driven Marangoni Convection in Polymer Thin Films to Generate Topographic Patterns Chae Bin Kim, Dustin Janes, Talha Arshad, Joshua Katzenstein, Nathan Prisco, Dana McGuffin, Roger Bonnecaze, Christopher Ellison The Marangoni effect describes how fluid flows in response to gradients in surface energy. We recently developed a method for photochemically preprograming spatial surface energy patterns in glassy polystyrene (PS) thin films. UV irradiation through a mask selectively dehydrogenates the PS, thus increasing surface energy in the UV exposed regions compared to the unexposed regions. After heating the film to the liquid state, transport of polymer occurs from regions of low surface energy to regions of high surface energy. This method can be harnessed to rapidly manufacture polymer films possessing prescribed three-dimensional topographies reflective of the original light exposure pattern. To quantify and verify this phenomenon, a theoretical model that gives a more thorough understanding of the physics of this process, its limits and ways to apply it efficiently for various target metrics will also be presented along with comparisons between theoretical predictions and experimental observations. Finally, while PS dehydrogenation can be used to produce a variety of topographical patterns, judicious selection of the photosensitizing compounds in an otherwise transparent polymer expands the use of this method to more readily available light sources. [Preview Abstract] |
(Author Not Attending)
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P1.00266: Work of adhesion and separation between soft elastomers Nanshu Lu The JKR (Johnson-Kendall-Roberts) method is widely used to measure the work of adhesion between soft materials. In this paper, the JKR theory is summarized and three dimensionless parameters are proposed to design a proper JKR experiment. The work of adhesion and the work of separation between two commonly used soft elastomers PDMS (Sylgard 184) and Ecoflex 0300 are obtained with the measured pull-in and pull-off forces using a dynamical mechanical analyzer (DMA). The effect of crosslinking density and solvent extraction are examined. It is found that the pull-in adhesion stays more or less constant for all contact pairs we measured. While the effect of crosslinking density is not significant for pristine PDMS, it is very obvious that the higher self-adhesion can be found in less crosslinked PDMS after solvent extraction. Such an effect is even more drastic for PDMS-to-Ecoflex adhesion. A unified adhesion mechanism is proposed to explain these complex adhesion behaviors. It is concluded that the chain-matrix interaction is the most effective adhesion mechanism compared to chain-chain or matrix-matrix interactions and the three interactions are exclusive to each other. [Preview Abstract] |
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P1.00267: BLOCK COPOLYMER THIN FILMS |
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P1.00268: The Effect of Hydrogen Bonding on the interfacial width of PS-b-PMMA Block Copolymer Microdomains Kyuseong Lee, Sunghyun Han, Sangshin Jang, Jicheol Park, Jongheon Kwak, Jin Kon Kim Sharp interface between two blocks in block copolymer nano pattern is one of the important issues because of strong demand in industrial applications to nano-patterning. We utilized hydrogen bonding between N-(4-aminomethyl-benzyl)-4-hydroxymethyl-bezamide (BA) and urea (U) at the interface of polystyrene-block-poly(methyl methacrylate) copolymer (PS-PMMA). For this purpose, we first synthesized PS by ATRP method, then the end group was converted to amino group. Next, it was reacted with BA, followed by reaction with 4-pentynoic acid, resulting in alkyne-terminated group (PS-U-BA-alkyne). Also, azide-terminated PMMA was prepared by anionic polymerization followed by end functionalization. Finally, by the azide-alkyne click reaction between PS-U-BA-alkyne and PMMA-azide, PS-U-BA-PMMA was synthesized. We investigated, via small angle X-ray scattering and transmission electron microscopy, phase behavior of PS-U-BA-PMMA. [Preview Abstract] |
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P1.00269: Long-Range Ordering of Block Copolymers on Well-Controlled Patterned Substrates Dong-Eun Lee, Nam-Kyun Kim, JiNa Park, DongHyun Lee In this study, we achieved long-range ordering of block copolymers (BCPs) by combining solvent-annealing process and well-controlled patterned substrates. Nano-lines of poly(tetrafluoro ethylene) (PTFE) were firstly fabricated in large area as a PTFE bar was rubbed on Si substrates at 340 $^{\circ}$C. The amplitude and pitch distance of PTFE nanolines were around 17 nm and 150 nm, respectively. Then, asymmetric polystyrene-\textit{block}-poly(2-vinylpyridine) copolymers (PS-$b$-P2VP) were subsequently spin-coated on the patterned substrates after a thin layer of poly(vinyl alcohol) (PVA) was prepared on the PTFE patterned substrates to enhance the wettability of BCP thin films. As BCP thin films were solvent-annealed in vapor of organic solvents, highly ordered BCP nanostructures oriented either parallel or perpendicular to the surface were generated in large area. In addition, the nanopatterns were successfully transferred to the underlying PVA layer or Si substrate by dry etching. Thus, the resulting nanopatterns were utilized as templates to synthesize inorganic nanofeatures. The ordering behavior of BCP thin films on the patterned substrates was characterized by using AFM, SEM and GI-SAXS. [Preview Abstract] |
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P1.00270: Macroscopic Alignment of Cylindrical Block Polymer Thin Film via Raster Solvent Vapor Annealing with Soft Shear Ming Luo, Douglas Scott, Thomas Epps One challenge associated with the utilization of block polymer thin films in nanotechnology is the difficulty of orienting and aligning the self-assembled nanostructure on macroscopic length scales, as block polymers typically self-assemble in an isotropic manner in the absence of surface forces and external fields. In this work, macroscopic alignment of block polymer cylinders was achieved through raster solvent vapor annealing with soft shear. Spatial control over nanoscale structures was accomplished through the application of a solvent vapor delivery nozzle, poly(dimethylsiloxane) shearing pad, and motorized stage. Complex patterns such as dashes, cross-shapes, and curved structures were demonstrated along with the possibility of scale-up for industry production. The simplicity of instrumentation and the versatility of patterns possess advantages over other directed self-assembly methods that are currently available. [Preview Abstract] |
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P1.00271: Tracking Solvent Uptake in Block Polymer Thin Films during Solvent Vapor Annealing Cameron Shelton, Ronald Jones, Joseph Dura, Thomas Epps A key goal in the block polymer (BP) thin films community is the design of a template-free, universal annealing method to control nanoscale self-assembly over large length scales. Solvent vapor annealing (SVA) offers a unique solution to this challenge with its ability to tune substrate surface, free surface, and polymer-polymer interactions by exposing films to appropriate solvents. However, there is little understanding of how the solvent behaves during the SVA process. In this work, we utilized the combination of deuterated solvents with small-angle neutron scattering (SANS) and neutron reflectometry to track solvent uptake in poly(styrene-b-isoprene-b-styrene) thin films. Two solvents were chosen for this analysis: d-hexane (isoprene selective) and d-benzene (styrene selective). Our work has shown that solvent choice and partial pressure have a significant impact on how solvent segregates within individual polymer domains and the film as a whole, directly impacting the restructuring of polymer domains. This work provides further understanding of the mechanism behind SVA, thereby making it easier to select appropriate conditions for desired self-assembly control. [Preview Abstract] |
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P1.00272: ABSTRACT WITHDRAWN |
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P1.00273: Optimization and Characterization of Self-assembled Triblock Polymer Membranes with Chemically-Tunable Pore Walls for Nanofiltration Applications Jessica Sargent, Ryan Mulvenna, Rafael Prato, Jacob Weidman, William Phillip, Bryan Boudouris The field of block polymer-based membranes for separation applications has grown considerably in the past several years. However, decreasing the domain sizes of these membranes to below 5 nm has proven to be a challenge in many instances. Here, we demonstrate that a triblock polymer, polyisoprene-$b$-polystyrene-$b$-poly(\textit{tert}-butyl methacrylate) (PI-PS-PtBMA), can be utilized to form nanoporous membranes capable of high flux and high selectivity based on both size and chemical composition. By controlling the synthesis, solution self-assembly, and non-solvent induced phase separation of these polymers, a scalable fabrication process can produce thin-film membranes that feature monodisperse pores approaching 1 nm in diameter, tunable pore-wall chemistry, good mechanical stability, and chlorine degradation resistance. The PtBMA functionality can further be converted to a number of side chain functionalities through simple coupling chemistry to produce membranes with specific chemical and structural characteristics tailored to meet the needs of various applications. In particular, these membranes provide a promising, inexpensive platform for chlorine degradation and fouling-resistant membranes for water purification that can be produced on an industrial scale. [Preview Abstract] |
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P1.00274: Thin Films of Bottlebrush Block Copolymers with Homopolymer Gajin Jeong, Benjamin R. Sveinbjornsson, Robert Howard Grubbs, Thomas P. Russell We have investigated the self assembled structures of bottlebrush block copolymers (BrBCPs) in thin films by blending deuterated homopolymer. By use of neutron reflectivity (NR), the assemblies with microdomain oriented parallel to the substrate, the distribution of the homopolymer in the bottlebrush block copolymer was obtained. Polynorbornene-backbone-based bottlebrush BCPs with polylactide (PLA) and polystyrene (PS) side chains of different molecular weights were investigated. Small angle x-ray scattering was used to complement the NR studies. [Preview Abstract] |
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P1.00275: Investigation of solvent annealing time dependence on morphology formation in polystyrene--\textit{block}--polylactide thin films Ryan Gnabasik, Gunnar Nelson, Andrew Baruth Solvent vapor annealing exposes a block polymer film to the vapors of one or more solvents, swelling the film. This process increases polymer mobility and can direct a self-assembly process by tuning the surface energy. Despite its efficacy to produce well-ordered, periodic nanostructures, no standardized production scheme exists. This is primarily due to a lack of understanding the intricate role multiple, incommensurate parameters play. By analogy to thermal annealing of elemental solids, the time a thin film spends in an equilibrium solvent concentration is one factor that will dictate the degree of ordering. To elucidate, optimized annealing conditions for perpendicular cylinder forming polystyrene-\textit{block}-polylactide exist at solvent concentrations just below the order-disorder transition, where the kinetic and thermal processes required for recrystallization and crystal growth are optimally fast (similar to thermal annealing). By use of a purpose-built, climate-controlled solvent annealing chamber, we map out the annealing time dependence for non-optimized solvent concentrations. Namely, at lower solvent concentrations, where mobility is limited, longer times are required for large lateral correlation lengths. \textit{In situ} spectral reflectance monitors solvent concentration, regulated \textit{via }a mass-flow controlled solvent inlet, offering precision control over annealing. Atomic force microscopy, in conjunction with O$_{\mathrm{2}}$ plasma etching, provides 3-dimensional imaging of the nanoscale morphology. This work was funded by NASA Nebraska Space Grant. [Preview Abstract] |
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P1.00276: Controlling Structure in Sulfonated Block Copolymer Membranes Phuc Truong, Gila Stein, Joe Strzalka In many ionic block copolymer systems, the strong incompatibility between ionic and non-ionic segments will trap non-equilibrium structures in the film, making it difficult to engineer the optimal domain sizes and transport pathways. The goal of this work is to establish a framework for controlling the solid-state structure of sulfonated pentablock copolymer membranes. They have ABCBA block sequence, where A is poly(t-butyl styrene), B is poly(hydrogenated isoprene), and C is poly(styrene sulfonate). To process into films, the polymer is dissolved in toluene/n-propanol solvent mixtures, where the solvent proportions and the polymer loading were both varied. Solution-state structure was measured with small angle X-ray scattering (SAXS). We detected micelles with radii that depend on the solvent composition and polymer loading. Film structure was measured with grazing-incidence SAXS, which shows (i) domain periodicity is constant throughout film thickness; (ii) domain periodicity depends on solvent composition and polymer loading, and approximately matches the micelle radii in solutions. The solid-state packing is consistent with a hard sphere structure factor. Results suggest that solid-state structure can be tuned by manipulating the solution-state self-assembly. [Preview Abstract] |
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P1.00277: Capillary forces induced wrinkling onto ultrathin single and bilayer polymer films Jooyoung Chang, Joseph Paulsen, Kamil Toga, Narayanan Menon, Thomas Russell We have studied wrinkling phenomena on ultrathin polymer sheets floated onto the aqueous media. As previously studied (\textit{Science}, 2007, 317(5838), 650--653, and \textit{Soft Matter}, 2013, 9, 8289--8296), the capillary forces of a water droplet placed on a floating sheet generate compressive hoop stresses, causing the sheet to wrinkle. In our current work, we investigate this phenomenon over a broader range of film thicknesses (7 nm to 950 nm) of Polystyrene (PS), Poly(methyl methacrylate) (PMMA), as well as with PS/PMMA bilayers. We report that the Young's modulus of PS (Mw: 97K) inferred from the wrinkle pattern is not significantly affected even if the thickness of PS is less than 10 nm. Furthermore, we also show that the type of the polymer (i.e. PS or PMMA) of the bottom layer of the bilayer system affects the length of the wrinkles. [Preview Abstract] |
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P1.00278: POLYMER COMPOSITES |
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P1.00279: Electrical Properties of PVDF Based Nanocomposites Jerry Contreras, Heinrich D. Foltz, Yuping Duan, Hasina F. HHuq, Steven C. Tidrow, Mircea Chipara Nanocomposites based on polyvinylidene fluoride (PVDF) have been obtained by melt mixing, loading the polymeric matrix with various weight fraction (between 0 {\%} to 40 {\%}) of different fillers (multiwalled carbon nanotubes, carbon nanofibers, and barium titanate). Pellets of nanocomposites have been obtained by hot pressing at about 175 $^{\mathrm{o}}$C. Copper contacts have been deposited on the as obtained pellets and the electrical features have been measured by using the two point technique. PVDF is a semicrystalline ferroelectric and piezoelectric polymer with a glass transition temperature of -35 $^{\mathrm{o}}$C and a melting temperature of about 175 $^{\mathrm{o}}$C. Electrical measurements have been performed in a wide range of frequencies starting from dc to ac (up to about 250 MHz). The dependence of the resistivity and dielectric constant on frequency and temperature (between -50 $^{\mathrm{o}}$C to 150 $^{\mathrm{o}}$C) was investigated in detail. Supplementary DSC, WAXS, and Raman data provided detailed information regarding the effect of fillers on phase transitions (glass, crystallization, and melting) and crystalline composition/structure of these nanocomposites. [Preview Abstract] |
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P1.00280: Additive-Driven Assembly of Block Copolymer and Nanoparticles: Influence of Nanoparticle Size and Loading Yue Gai, Ying Lin, James Watkins Additive-driven assembly of block copolymer (BCP)/nanoparticle (NP) composites in which functionalized NPs exhibiting strong hydrogen bond interactions with one domain of the BCP has been shown to strengthen phase segregation and yield well-ordered materials at high NP loadings. Here we report a systemic study of how phase behavior and NP distribution in BCP/ Au NP composites are influenced by the NP size, NP loading and block copolymer domain size. 2nm, 5nm, 9nm and 15nm diameter Au nanoparticles at loadings ranging from 10{\%} to 50{\%} weight percent, in polystyrene-block-poly (2-vinyl pyridine) block copolymers with domain spacing ranging from 14 nm to 75 nm were used in the investigation. We find that strong interactions enable the incorporation of larger diameter NPs with respect to domain size as compared to systems in which interactions between the NP and BCP are weak or enthalpically neutral. [Preview Abstract] |
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P1.00281: Mechanically Robust Polymer-Graphene Aerogels Heonjoo Ha, Kadhiravan Shanmuganathan, Christopher Ellison Graphene has been intensely studied for the past several years due to its many attractive properties. Graphene oxide (GO) aerogels are particularly interesting due to their light weight and excellent performance in various applications, such as environmental remediation, super-hydrophobic and super-oleophilic materials, energy storage, etc. However, GO aerogels are generally weak and delicate which complicates their handling and potentially limits their application outside the research lab. The focus of this work is to synthesize mechanically stable aerogels that are robust and easy to handle without substantially sacrificing their low density. To overcome this challenge, we found that by intermixing a small amount of readily available and thermally crosslinkable polymer can enhance the mechanical properties without disrupting other characteristic intrinsic properties of the aerogel itself. This method is a simple straight-forward procedure that does not include any tedious chemical reactions or harsh chemicals. Furthermore, we will demonstrate the performance of these materials as a super-absorbent and pressure sensor. [Preview Abstract] |
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P1.00282: Life-time of the bound layer in nanocomposites Dan Zhao, Jacques Jestin, Sanat K. Kumar It is now well accepted that an effectively irreversibly adsorbed monolayer of polymer forms when a polymer melt is intimately mixed with nanoparticles, in the limit where their enthalpic interactions are favorable. This bound layer has been postulated as being a central player in many of the highly favorable properties that result from polymer based nanocomposite materials. We investigated well-defined nanocomposites formed with different combinations of deuterated and hydrogenated polymers (P2VP and PMMA) and silica nanoparticles. SANS, in conjunction with contrast variation, then provides a direct means of probing the structure of the bound layer as a core-shell and its exchange kinetics with bulk (unbound) chains with annealing time and temperature. SAXS directly provides information on the particle-particle partial structure factor and particle dispersion. Thermodynamic equilibrium of the bound layer is reached around one day at 150 $^{\circ}$C while its exchange life time is $\sim$ one hour at 180 $^{\circ}$C. [Preview Abstract] |
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P1.00283: POLYMER NANOCOMPOSITES: ACTIVE PARTICLES AND DYNAMICS |
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P1.00284: Unusual dielectric loss properties of carbon nanotube - polyvinylidene fluoride composites in low frequency region (100 Hz \textless f \textless 1 MHz) Guang-Lin Zhao, Yi Zhen, Juan Arredondo Systematic investigations on the dielectric properties of multi-walled carbon nanotubes (MWCNTs)-polyvinylidene fluoride (PVDF) composites with a wide MWCNT concentration range (2-9wt{\%}) have been carried out. It was revealed that the dielectric constant are increased by the addition of an appropriate amount of MWCNTs at room temperature. However, when the concentration of MWCNTs in the composites reaches above 5wt{\%}, negative dielectric constants and large dielectric loss in the composites are observed in the low frequency range. The ferroelectric CNT-PVDF polymer composites containing more than 5 wt{\%} MWCNTs have a strong dielectric absorption, which has the potential for acoustic applications. [Preview Abstract] |
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P1.00285: Dispersion of bimodal polymer brushes functionalized anisotropic gold nanoparticles in polymer nanocomposites Lili Zhu, Gi Xue, Linda Reven Polymer nanocomposites (PNCs), which are composed of the nanofiller component and polymer matrix, have attracted growing interests due to their fascinating properties. Great efforts have been made to achieve high compatibility between the nanofillers and the polymer matrix. The dispersion of spherical gold nanoparticles (GNPs) in the matrix have been extensively studied, while there are few studies using anisotropic GNPs. The goal of this work is to produce homogeneous PNCs of anisotropic NPs in stimuli responsive polymer matrix. We compared the dispersion of gold nanoprisms (GNPRs) with single and bimodal poly(2-vinylpyridine) P2VP brushes. Bimodal brushes consisted of mixture of low and high molecular weight (Mw) polymers. GNPRs with P2VP were dispersed into polymer matrix and the Mw of the matrix was systematically varied to investigate the Mw effect. UV-Visible-Near Infrared spectroscopy was utilized to monitor the special plasmonic properties and architectures of GNPRs. The dispersion and morphology of PNCs were characterized by electron microscopy. This work will help to establish the correlations between the properties of anisotropic NPs (shape and protecting ligands) and the miscibility of corresponding PNCs. [Preview Abstract] |
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P1.00286: Time-resolved WAXD studies on the crystallization of isotactic polypropylene/graphene nanocomposites Shotaro Nishitsuji, Maya Endoh, Yichen Guo, Miriam Rafailovich, Tadanori Koga Graphene is one layer of carbon atoms, which has good electronic, thermal conductivity and mechanical properties. By adding graphene to isotactic polypropylene (iPP), the mechanical and electrical properties of the polymer are significantly improved. To further achieve high performance of iPP/graphene nanocomposites (``NCs''), it is important to investigate the relationship between the crystalline structure of iPP and the mechanical property of the iPP/graphene NCs. In this study, the effect of the graphene on the crystallization behavior of the polymer was investigated by using time-resolved wide angle X-ray diffraction (WAXD). The iPP/graphene NCs with different weight ratios of graphene were prepared by using a twin screw extruder. After temperature jump from 210 $^{\circ}$C (\textgreater Tm) to 170 $^{\circ}$C, the melt-crystallization process was observed by in situ WAXD. The results showed that the crystalline structure of all the samples was still $\alpha $-form that is the same as the neat PP, while the ratios of the diffraction peaks are quite different from those of the neat PP. We will discuss the detailed structure in this presentation. [Preview Abstract] |
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P1.00287: Rheology and Phase Transitions in Highly Filled Additive/Block Copolymer Composites Benjamin M. Yavitt, Rohit Kothari, H. Henning Winter, James J. Watkins We have recently demonstrated that strong, segment-specific interactions between multi-functional additives (organics, nanoparticles and nanotubes) and one segment of a block copolymer can yield highly filled, well-ordered composites. In this study we used rheology to determine phase transitions and materials properties in systems containing high volume fractions of nanoparticles that are not accessible in by other means. We utilized well-defined surface functionalized nanoparticle systems by which we can assess the role of the number, strength, and surface density of functional groups on the phase behavior and mechanical properties of the composites. From this study, we developed an understanding of the interactions and structure between nanoparticles and block copolymer, and the mechanisms by which these characteristics are affected by temperature. [Preview Abstract] |
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P1.00288: PEO-MWCNTs Nanocomposites: The Effect of the Nature of Solvent on the Morphology and Physical Properties of Nanocomposites Alfonso Salinas, Charles Cartwright, Kevin L. Newcombe, Mircea Chipara, Ibrahim Elamin, James Hinthorne, Dorina M. Chipara, Karen Lozano PEO nanocomposites have been obtained by dissolving the polymer within selected solvents (water, ethanol, toluene, and chloroform), addition of the nanofiller (Multiwalled Carbon Nanotubes: MWCNTs), dispersion of the as obtained mixture by stirring at 500 rotation per minute for 1 h followed by a sonication for 30 minutes using a high power sonicator (500 W), and solvent evaporation in an oven at 110 $^{\circ}$C, for 10 h. Nanocomposites containing 0 to 40 {\%} wt. MWCNTs have been obtained and investigated. Scanning Electron Microscopy was used to assess the dispersion of MWCNTs within the polymeric matrix. Wide Angle X-Ray Scattering, Raman, FTIR, and UV-VIS were used to characterize the crystalline structure and molecular/atomic motions in the as obtained samples. Differential Scanning Calorimetry was used to estimate the glass, crystallization, and melting temperatures. Thermal stability will be questioned by thermogravimetric analysis. The effect of the nature of the solvent on the dispersion of nanotubes and on the physical properties of the as obtained nanocomposites will be analyzed in detail. [Preview Abstract] |
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P1.00289: Photo-actuating waveguiding fibers based on light responsive hydrogels Ying Zhou, Adam Hauser, Nathan Rasmussen, Mark Kuzyk, Ryan Hayward The combination of light-absorbing nanoparticles with thermally sensitive hydrogels has been widely explored as a strategy for photo-thermal actuation. Here, we employ a system of photo-crosslinkable copolymers containing pendent benzophenone units to prepare planar waveguiding polymethylmethacrylate(PMMA) fibers patterned with poly(N-isopropyl acrylamide) (PNIPAM) copolymer hydrogels containing Au nanoparticles. These structures show both thermally- and photo-actuated bending behavior due to swelling stresses developed in the PNIPAM gel layer. Further, we establish that light can be successfully guided into micro-patterned fibers, yielding a route to remotely controlled micro-actuators. [Preview Abstract] |
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P1.00290: Polymer Grafted Nanoparticle-based Oil Dispersants Daehak Kim, Ramanan Krishnamoorti Particle-based oil dispersants mainly composed of inorganic nanoparticles such as silica nanoparticles are considered as environmentally friendly oil dispersants due to their biocompatibility and relatively low toxicity. The oil-water interfacial tension is reduced when nanoparticles segregate to the oil-water interface and this segregation is improved by grafting interfacially active polymer brushes. In this study, surfactant-like amphiphilic block copolymers were grafted from silica nanoparticles using an atom transfer radical polymerization (ATRP) method in order to increase their interfacial activity. We have studied the interfacial activity of such hybrid nanoparticles using pendant drop interfacial tension measurements, and their structure using small angle X-ray scattering. Amphiphilic copolymer grafted nanoparticles significantly reduced oil-water interfacial tension compared to the interfacial tension reduction induced by homopolymer grafted nanoparticles or the corresponding free ungrafted copolymer. Moreover, hard and stable oil-water emulsions were formed by applying the block copolymer grafted nanoparticles due to the formation of interparticle network structures, which were observed by cryo-scanning electron microscopy (SEM) and small angle neutron scattering (SANS) [Preview Abstract] |
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P1.00291: PNIPAM grafting on the surface of zirconium phosphate Hai Li, Xuezhen Wang, Zhengdong Cheng We are reporting for the first time the grafting of the thermoresponsive polymer PNIPAM (poly n-isoproprylacrylamide) on the surface of inorganic nanoplates zirconium phosphate. Particularly, the grafting on inorganic nanoplates using gamma rays has never scarcely been reported and yet proved to be successful in our synthesis. We proved that by gamma ray irradiation, the peroxide groups has been produced on the ZrP particles since that peroxide groups, on the surface of the hexagonal nanoplates, which upon heating initiated the free radical polymerization and subsequent attachment of PNIPAM. The presence of covalent band between ZrP and PNIPAM were observed and characterized by TGA, FTIR and solid state NMR respectively. The attachment of a thermoresponsive polymer to ZrP nanocrystals brings thus remarkable possibilities for their employment in the fields of medicine, oil industry, as well as physics. [Preview Abstract] |
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P1.00292: Toward Designer Nanoparticle Assemblies: Supramolecular Nanocomposites on Patterned Surfaces Katherine Evans, Joseph Kao, Ting Xu Nanoparticles have unique properties due to the quantum confinement effect. Controlled assemblies of nanoparticles of different sizes and chemical composition are predicted to have new optoelectronic properties. Supramolecules are ideal structural framework to guide nanoparticle assemblies in thin films without modifying the particle ligand chemistry. We recently showed that optically patterned trench patterns can effectively guide the assembly of supramolecular nanocomposites over micrometer to form aligned nanoparticle lines. I will report our recent investigation on more complex patterns to evaluate how the curvature of the pattern affects the nanoparticle assembly. Preliminary studies show potential for controlling and tailoring nanoparticle assemblies, and in turn, the optical properties of such assemblies. [Preview Abstract] |
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P1.00293: Fluorescence in nanocomposites based on polyethylene oxides and block copolymers of polyethylene oxide-polypropylene oxide loaded with rare earth doped fluorides Brian Yust, Francisco Pedraza, Dhiraj Sardar, Aaron Saenz, Mircea Chipara Rare earth doped fluoride nanoparticles with a size of about 25 nm have been synthesized by a solvothermal process. Polymer-based nanocomposites, containing various weight fraction of nanofillers, have been obtained by dissolving the polymeric matrix (polyethylene oxide) within a solvent (deionized water), adding the nanoparticles, sonicating the mixture, and finally removing the solvent. The complete removal of the solvent has been confirmed by Thermogravimetric Analysis. Additional information about the thermal features have been obtained by Differential Scanning Calorimetry, Wide Angle X-Ray Scattering, FTIR, UV-Visible, and Raman. The effect of the loading with nanoparticles on the glass, crystallization, and melting transition temperatures of the polymeric matrix are reported. Fluorescence of rare earth doped nanoparticles dispersed within the polymeric matrix has been tested by laser spectroscopy. The dependence of fluorescence intensity on the concentration of nanofillers and on temperature in the range 300 to 400 K is analyzed. [Preview Abstract] |
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P1.00294: Anisotropic Polymer Conformations in Aligned SWCNT/PS Nanocomposites Wei-Shao Tung, Russell Composto, Nigel Clarke, Karen Winey In our previous study of isotropic SWCNT/polystyrene (PS) nanocomposites, we found that the polymer radius of gyration (Rg) increases and the SWCNT mesh size decreases with increasing SWCNT concentration. Here, we investigate the effect of aligning SWCNTs on Rg and the SWNCT mesh. SWCNT alignment was accomplished by melt fiber spinning or extrusion, and small angle neutron scattering was used to probe the structure. As expected, SWCNT alignment produces anisotropic meshes. Below 2 wt{\%} SWCNT, no significant change in Rg is observed and Rg parallel and perpendicular to the direction of SWCNT alignment are comparable. More interestingly, at higher wt{\%} SWCNT the polymer conformations are anisotropic with a larger Rg perpendicular to the SWCNT than along the SWCNT. For example, with 6 wt{\%} SWCNT, the Rg perpendicular to the SWCNT is $\sim$ 15{\%} larger than parallel to the SWNCT. This anisotropy in the polymer conformation becomes more prominent at higher SWCNT concentrations, perhaps because at higher SWCNT concentrations the distribution of mesh shifts to smaller meshes (\textless 2Rg) so that a single polymer chain interacts with multiple SWCNTs. Implications of this finding will be discussed. [Preview Abstract] |
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P1.00295: THE PHYSICS OF CONFINED FLUIDS |
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P1.00296: Capillary instability of periodic polymer structures: Influence of viscosity, substrate confinement and local curvature Zheng Zhang, Yifu Ding We investigate the simultaneous capillary instability among periodic polymer lithographic structures suspended on an immiscible viscous medium. The first system we studied was straight polystyrene (PS) stripes arranged in parallel in PMMA medium. When annealed at a temperature above the glass transition temperature of both polymers, the stripes undulated and then ruptured via capillary instability. We found that the PS-to-PMMA viscosity ratio strongly affected the rupture kinetics, while it had little influence on the rupture wavelength. The rupture behavior of those stripes could be drastically altered due to initial spacing and substrate confinement. For closely-neighboring stripes that were confined on a rigid substrate, the capillary waves became correlated in-phase among neighbors. Under strong confinement, the capillary rupture was always correlated, irrespective of the viscosity ratio. In addition, we examined the influence of in-plane curvature on capillary instability in concentrically arranged PS rings. When the rings were relatively far apart, their rupture behaviors were independent from each other; when they were close to each other, the primary mode in the capillary breakup became strongly correlated from the center towards the peripheral. [Preview Abstract] |
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P1.00297: Static and Dynamic Capillary Forces in Pollen Adhesion and Detachment Carson Meredith, Donglee Shin, Haisheng Lin Nature provides remarkable examples of adhesive bioparticles including diatoms, pollens, and fungal spores, which are robust examples of nature's solutions to particle adhesion. These particle's interactions are often mediated by liquid films at micro- and nanometer length scales, and their study can lead to new physical insights into confined fluids. This talk will detail recent discoveries of the wet adhesive mechanisms of pollen, which provide useful insights into the role of capillary forces and confined fluids in nature. In particular, we describe how pollenkitt, a viscous fluid coating many pollen particles, forms nanoscale capillary bridges that mediate the adhesion and detachment of pollens from surfaces of insects and plants. We will present experimentally observed static and dynamic regimes of pollenkitt capillary forces. Models are utilized to understand the role of rheological properties of pollenkitt in creating these forces. Importantly, the forces generated by pollenkitt give pollen attachment and release from surfaces a sensitive dependence on humidity, rate, and surface morphology. This talk will explore how the physics of these forces contributes to pollenation in nature and how they might be harnessed to engineer new materials. [Preview Abstract] |
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P1.00298: EXTREME MECHANICS: CONTORTION OF RILAMENTS, RIBBONS AND BUNDLES |
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P1.00299: EXTREME MECHANICS OF ORIGAMI: FOLDING, MECHANISMS AND MECHANICS |
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P1.00300: Hysteretic self-folding of micro-scale polymer origami films Jun-Hee Na, Jesse Silverberg, Arthur Evans, Christian Santangelo, Thomas Hull, Itai Cohen, Ryan Hayward Origami-inspired self-folding materials have attracted interest for the design of actuators and remotely deployable devices. While well-established geometric rules have been used to create rigidly self-foldable origami structures, the behavior of non-rigidly foldable crease patterns remains incompletely understood. In particular, understanding the relationship between crease geometry and the resulting elastic energy barrier remains a central challenge. Here, we describe a simple model system based on the well-known square twist folding pattern to explore how self-folding structures overcome such energy barriers, and the resulting hysteresis in the folding/unfolding behavior. We show that the magnitude of the hysteresis can be tuned by variations in the plane angle characterizing the crease pattern, as well as by selectively weakening the panel diagonals to reduce the energy cost of bending. These results provide insights into geometrically-controlled energy barriers in non-rigidly foldable origami and design rules for the construction of bistable self-folding systems. [Preview Abstract] |
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P1.00301: CONFORMATIONS AND DYNAMICS OF BIOPOLYMERS |
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P1.00302: Conformations and dynamics of a translocating semi-flexible chain through a Nano-pore facilitated by chaperones Ramesh Adhikari, Aniket Bhattacharya We have studied the translocation dynamics of a semi-flexible polymer through a nano-pore from $cis$ to $trans$ compartment containing binding particles (chaperones) which introduce a bias for the translocating chain. We have used a model semi-flexible polymer using excluded volume (Lennard-Jones), anharmonic spring (elasticity), and three-body bond bending (chain stiffness) potentials, and applied Langevin dynamics simulation to study various aspects of conformations and dynamics of the translocating chain. In particular, we have investigated the conditions for the most efficient translocation as a function of the chain stiffness, strength of the attractive interaction, and the density of the binding particles, reflected in the mean first passage time (MFPT) of translocating chain through the pore. We have observed that for certain binding strengths and concentrations of the chaperons, the translocation is faster than the ideal Brownian ratchet (BR) process [Simon {\em et al.}, Proc. Natl. Acad. Sci. U.S.A. {\bf 89}, 3770 (1992)]. [Preview Abstract] |
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P1.00303: Uncovering the effect of DNA topology on the mobility and conformational dynamics of crowded DNA molecules Stephanie Gorzcyza, Cole E. Chapman, Rae M. Robertson-Anderson Using single molecule fluorescence microscopy and particle-tracking, we examine the effects of crowding on the diffusion and conformation of large, double-stranded circular DNA molecules. To determine diffusion, we track the mean-squared-displacement of single fluorescent-labeled DNA molecules embedded in solutions of different crowding agents. Using image analysis techniques, we also characterize the conformational change (from random coil configuration) induced in DNA by crowding. Our previous studies with linear DNA crowded by dextran reveal crowding-induced mobility reduction of DNA, dependent on crowder size, and elongation of DNA random coils, dependent on DNA size. Here, we compare our previous results to those for circular DNA crowded by varying crowding agents including dextran, Ficoll and Polyethylene Glycol. We determine the dependence of circular DNA mobility and conformation on the level of crowding, molecular weight of the crowding agent, structure of the crowder, and DNA length (11-115 kilobasepairs). Thus, this research uncovers the underlying mechanisms responsible for observed DNA dynamics in crowded environments and biological cells. [Preview Abstract] |
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P1.00304: DYNAMICS OF GLASSY POLYMERS UNDER CONFINEMENT |
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P1.00305: Glass transition cooperativity from broad band heat capacity spectroscopy Yeong Zen Chua, Gunnar Schulz, Evgeni Shoifet, Heiko Huth, Reiner Zorn, Juern W.P. Schmelzer, Christoph Schick Molecular dynamics is often studied by broad band dielectric spectroscopy (BDS) because of the wide dynamic range available and the large number of processes resulting in electrical dipole fluctuation and with that in a dielectrically detectable relaxation process. Calorimetry on the other hand is an effective analytical tool to characterize phase and glass transitions by its signatures in heat capacity. In the linear response scheme, heat capacity is considered as entropy compliance. Consequently, only processes significantly contributing to entropy fluctuations appear in calorimetric curves. The glass relaxation is prominent example for such a process. Here we present complex heat capacity at the dynamic glass transition (segmental relaxation) of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in a dynamic range of 11 orders of magnitude, which is comparable to BDS [1]. As one of the results, we determine the temperature dependence of the characteristic length of the corresponding fluctuations. The characteristic length decreases from about 4 nm to about 0.7 nm in the temperature range from 370 K to 500 K. This proves an estimate for possible confinement effects on the segmental relaxation, which is different from vitrification as discussed by Cangialosi \textit{et al}. [2]. [1] Y. Z. Chua \textit{et al}., Col {\&} Poly Sci \textbf{292}, 2014. [2] D. Cangialosi, J of Phys: Cond Matt \textbf{26} (15), 2014. [Preview Abstract] |
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P1.00306: STABLE GLASSES, PROPERTIES AND ORIGINS |
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P1.00307: Thermal Stability of Vapor-Deposited Stable Glasses of an Organic Semiconductor Diane Walters, Ranko Richert, Mark Ediger Organic glasses prepared by physical vapor deposition can be highly stable and resistant to transformation upon heating. Unlike ordinary glasses, transformation to the supercooled liquid is initiated at a free surface or other interface and propagates through the material as a constant velocity front. In this work, we show that an organic semiconductor commonly used as an active layer in organic electronics, TPD, transforms via propagating fronts when heated above the glass transition temperature. We measure transformation front velocities using spectroscopic ellipsometry. Using high-throughput preparation and annealing techniques, we find that front velocity can vary by over an order of magnitude depending upon the substrate temperature during the deposition of the glass. Transformation front velocity is also influenced by the mobility of the supercooled liquid at the annealing temperatures and, consistent with this view, transformation fronts have the same activation energy for stable glasses prepared with a wide range of the substrate temperatures. These results may aid in designing organic electronic devices with improved lifetimes. [Preview Abstract] |
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P1.00308: Effect of absorbed water on the thermodynamic and kinetic properties of vapor-deposited organic glasses Marta Gonzalez-Silveira, Cristian Rodriguez-Tinoco, Joan Rafols-Ribe, Aitor F. Lopeandia, Javier Rodriguez-Viejo Most organic glasses absorb water when exposed to ambient conditions. As a consequence, the glass can experiment changes in its physicochemical properties, being the triggering of crystallization one of the most inconvenient drawbacks. The amount of absorbed water depends on the partial pressure but also on the stability of the glass. Previous studies have shown that ultrastable indomethacin glasses absorb less water than the conventional counterpart. We show here how water absorption modifies the kinetic properties of the glass while, unexpectedly, the thermodynamic stability remains unaltered. By means of ex-situ and in-situ calorimetry, we analyze the relationship between water absorption and kinetic properties for glasses that are vapor-deposited at different temperatures around 0,85 Tg. Moreover, glasses exposed to water vapor exhibit a double glass transition, a clear indication of the presence in the glass of regions with different kinetic stability. [Preview Abstract] |
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P1.00309: Surface Self-diffusion of Organic Glasses and Low Molecular Weight Polystyrene Wei Zhang, Caleb Brian, Lian Yu The study of surface self-diffusion of organic glasses and low molecular weight polystyrene help understand the formation of stable glasses by vapor deposition, the nature of surface mobility on polymer glasses and the fast surface crystal growth. Surface self-diffusion was measured via surface grating decay. Corrugated patterns were embossed on sample surfaces with master gratings at elevated temperatures. The smoothing of surface gratings was monitored with Atomic Force Microscopy or light diffraction.$^{\mathrm{\thinspace }}$It was identified by Mullins' model that viscous flow dominates grating decay at high temperatures, but surface diffusion is the leading mechanism upon cooling. Surface diffusion coefficients were measured for organic glasses and polystyrenes with different glass transition temperatures and intermolecular forces. Surface diffusion is at least 10$^{\mathrm{5}}$ times faster than bulk diffusion at T$_{\mathrm{g}}$, and unlike bulk diffusion, surface diffusion exhibits strong material dependence. The fast surface diffusion implies fast rearrangement of molecules on surface during vapor deposition and helps the formation of stable glasses. [Preview Abstract] |
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P1.00310: Infrared spectroscopic investigation of stable glasses of indomethacin Jing Jiang, Mark Ediger Glasses with high density and kinetic stability can be prepared by physical vapor deposition. By varying the substrate temperature, stable glasses can be produced with an anisotropic distribution of molecular orientations. We use infrared transmission spectroscopy to investigate the effect of substrate temperature on the structure of indomethacin stable glasses. At normal incidence, height of peaks which are assigned to asymmetric hydrogen-bonded acid C=O stretching vary systematically with the substrate temperature. This indicates either more hydrogen-bonded acid carbonyl groups in the most stable glass or a dependence of molecular orientation upon substrate temperature can be shown by IR. [Preview Abstract] |
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P1.00311: MANIPULATING GLASSES |
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P1.00312: Non-affine reorganizations in glassy polymers under applied strain in the plastic regime Didier Long, Luca Conca, Alain Dequidt, Jean-Yves Delannoy, Paul Sotta, Fran\c{c}ois Lequeux A model for the dynamics of non-polar polymers, based on percolation of slow subunits, has been proposed and developed over the past ten years. This model has been extended for describing plastic deformation of glassy polymers. It has been proposed that the applied stress results in an acceleration of the dynamics of the subunits. At deformation amplitudes of a few percent, we can observe plastic yield. The onset of plasticity is accompanied by an increase of the non-affine nature of the deformation at microscopic scales. Localization phenomena are observed in the plastic regime. We present here a detailed study of the complex reorganization which takes place on a scale of a few nanometers. We show that the correlation length of non-affine deformation increases at yield, but remains finite, with typical value 10-20 nm, corresponding to typical distance between shear bands. We compare in detail the microscopic mechanisms at play during shear deformation, uni-axial extension and compression. [Preview Abstract] |
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P1.00313: POLYMERIC GLASSES |
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P1.00314: Volume Recovery of Polymeric Glasses N. Sakib, S.L. Simon Following the seminal work of Kovacs, capillary dilatometry has been used for the last fifty years to study volume recovery of polymeric glass formers. Our capillary dilatometer, which previously used a Linear Variable Differential Transducer (LVDT) to measure the height of the Hg column in the capillary, has been modified following the work of Richert. The current study demonstrates the use of a capacitance bridge as the transducer. A metallic layer of silver sputtered on the exterior of the dilatometer serves as the outer electrode, mercury (the confining fluid) serves as the inner electrode, and the glass in between serves as the dielectric of the capacitor. The Andeen-Hagerling 2550A 1kHz ultraprecision capacitance bridge is used for the measurements. Volume recovery of various glass formers will be used to test the new design; new measurements are planned to test models of structural recovery. [Preview Abstract] |
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P1.00315: Cure Kinetics of the Hydroxyl-Epoxide Reaction in DGEBA Epoxy Hardened with Diethanolamine Lebelo Hailesilassie, Narjes Fredj, Caitlyn M. Clarkson, John D. McCoy, Mathew C. Celina, Jamie M. Kropka The curing of a diglycidyl ether of bisphenol-A Epoxy (Epon 828) with diethanolamine (DEA) involves a fast amine-epoxide reaction followed by a slower hydroxyl-epoxide reaction. At curing temperatures below 70$^{\circ}$C, the time scales of these two reactions are well separated. This permits the study of the hydroxyl addition as an ``isolated'' reaction. The reaction is strongly auto-catalyzed and is well fit to a modified form of the Kamal equation. Here we study the temperature dependence of the Kamal parameters with modulated differential scanning calorimetry and infrared spectroscopy. [Preview Abstract] |
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P1.00316: Liquid Substrate Effects on the Glass Transition Temperature of Nanoscopically Confined Polystyrene Spheres Dane Christie, Chuan Zhang, Rodney Priestley The effect of the liquid-polymer interface on the glass transition temperature (T$_{g})$ of polystyrene (PS) was investigated using differential scanning calorimetry. Polystyrene nanoparticles of different radii were suspended in either water, glycerol or an ionic liquid. Particles suspended in water (or cast into a film in air) exhibited a T$_{g}$-confinement effect consistent with that of freestanding films of PS. Particles suspended in an ionic liquid exhibited an invariance in T$_{g}$ with confinement while those suspended in glycerol exhibit a modest, depression in T$_{g}$ with confinement. Upon re-suspension in water, particles formerly suspended in glycerol showed a partial recovery of their T$_{g}$ in water. However, particles re-suspended in water from an ionic liquid showed no recovery of their T$_{g}$ in water. These results are explained in the context of chain mobility and interfacial energy, and provide insight and a probable resolution to contradictory observations in the literature. [Preview Abstract] |
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P1.00317: POSTDEADLINE ABSTRACTS |
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P1.00318: Chirality Induced Spin Selectivity for Memory Applications Rahamim Guliamov, Shinto Mathew, Kiran Vankayala, Hagay Moshe, Yitzhak Mastai, Ron Naaman Creation and manipulation of spin current is one of major aspects of memory devices. In conventional devices spin-polarized current is created by permanent magnetic layer. Further miniaturization of the memory is limited by super-paramagnetic behavior of layer. Hence, high density memory requires out-of-plane geometry with perpendicular magnetic anisotropy. Achieving this goal with inorganic magnetic layers is a challenge. We present a new approach in which the permanent magnetic layer has been replaced with inorganic chiral film producing spin polarized current due to Chirality Induced Spin Selectivity (CISS) effect. Chiral Al$_{2}$O$_{3}$ film grown by ALD on self-assembled monolayer of chiral molecules acts as a spin filter. Spin polarization is parallel/antiparallel to the electron velocity depending on chirality. Devices show asymmetric magneto-resistance and slopes with opposite sign for left/right handed chirality. Hence, CISS-effect based device shows, for first time, an asymmetric magneto-resistance, which has potential application in magnetic memory and magnetic field sensors. Reference: Shinto P. Mathew et al., \textit{Appl. Phys. Lett.} 105, 242408 (2014) [Preview Abstract] |
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P1.00319: Proving grain boundaries and transport study of graphene grown on liquid Cu Seong-Yong Cho, Min-Sik kim, Ki-Ju Kim, Min-Su Kim, Hyun-Mi Kim, Sang-Hoon Lee, Ki-Bum Kim We revealed grain boundaries of graphene grown on liquid Cu via hydrogen etching and Cu oxidation, and found out that small gap and voids exist between graphene islands on liquid Cu due to small supersaturation ratio which was required for self-assembly to occur. Modified two-step growth was applied in order to fill the gap between graphene islands and continuous graphene was synthesized on liquid Cu. The continuity of the film was verified through hydrogen etching and NaCl assisted oxidation. Electrical resistance of graphene grown on liquid Cu was lower than graphene grown on solid Cu if there is no crack damage which might be resulted from thermal stress related solidification of Cu and wet-transfer. Also, Hall mobility of graphene grown on liquid Cu shows two times higher value compared to that of graphene grown on solid Cu. In order to verify the aligned grain boundary of graphene on liquid Cu, direct patterning enabled electrode deposition on two neighboring graphene single crystal which aligns in the same orientation. Gran boundary resistance was negligible based on our electrical measurement results which has a great potential impact on graphene growth on liquid Cu. [Preview Abstract] |
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P1.00320: Enhancement of Electromagnetically Induced Transparency Cooling by an Optical Cavity Wei Wu, Jie Zhang, Shuo Zhang, Bao-Quan Ou, Ping-Xing Chen One of the most popular methods for cooling trapped ions to ground state is sideband cooling. However, carrier and blue sideband still exist, which are the obstacles for reaching lower phonon number. EIT cooling cancels the carrier transition and suppressed blue sideband transition to some extent, blue sideband transition still exists. To further suppress the blue sideband transition and improve EIT cooling, Introducing an optical cavity provides us a promising way to enhance the EIT cooling and reach lower phonon number for a trapped ion. A $\Lambda$-configuration ion with mass $M$ is trapped in a Paul trap, we consider the situation that the radial confinement is much stronger than that of the axial direction, only one dimensional movement along the axis should be concerned. If we set the dutuning properly, EIT effect occurs, canceling the carrier transition, while the heating effect from blue sideband transition can be suppressed by quantum interference between the laser and cavity. Analytical calculation shows that cooling limit of this new scheme is \begin{equation} \langle n\rangle_{st} =\frac{1}{\mathcal{C}}, \end{equation} Numerical simulation shows that the standard EIT cooling is enhanced with the help of the high finesse cavity. [Preview Abstract] |
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P1.00321: Properties of Amorphous Transparent Conducting Oxides from First Principles: In-O, In-Zn-O, In-Sn-O, and Zn-In-Sn-O Rabi Khanal, Julia Medvedeva Systematic investigations of amorphous In-based oxides, In-X-O with X$=$Zn and/or Sn, obtained via ab-initio molecular dynamics liquid-quench simulations, are performed to understand the role of composition in the structural, optical, transport, and mechanical properties of these oxides. First, the structural characteristics of the first, second, and third shells are compared between amorphous In-O, In-Zn-O, In-Sn-O, and Zn-In-Sn-O. The results reveal that the local Metal-Oxygen structure for both In and X cations -- and hence, optical band gap and electron effective mass governed by the metal-oxygen interactions -- remains nearly intact upon the transition to amorphous state. In all amorphous oxides considered, Indium is undercoordinated with little dependence on X, whereas the X cations reach their natural coordination. This finding suggests that the carrier generation is primarily governed by In atoms, in agreement with transport measurements in the amorphous oxides. In contrast to the first shell, the composition affects the Metal-Metal distances, coordination, and oxygen sharing. The interconnectivity and spatial distribution of InO6 and XOx polyhedra limits the charge transport via scattering and ultimately determines the formation of the amorphous oxides and their properties. [Preview Abstract] |
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P1.00322: Perovskite Structured Oxide Thin Film as Photocapacitor Joyprokash Chakrabartty, Riad Nachache, Federico Rosei Photocapacitor is a device that converts solar energy through photovoltaic effect, and stores the converted energy by maintaining the charge concentration difference across a membrane upon light irradiation. It eliminates additional storage devices, for example, extra battery towards device miniaturization by enabling generated charge storage facilities in the same system. Till to date published reports show those devices that used artificial layer within single structure to make storage facility. Here we show some preliminary results on Bi-Mn-O thin film systems that differ from others in such a way that it will employ self-assembled system to convert and to store solar energy. [Preview Abstract] |
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P1.00323: Development of Magnetization Detecting Electron Spin Resonance Method Satoshi Matsuzawa, Hiroyuki Nojiri Electron spin resonance: ESR is a spectroscopy by using electromagnetic wave absorption in Zeeman spitted multiplet of spins. The split energy is determined by the resonance field and the line width is governed by relaxation and anisotropies. The absorption intensity is proportional to the population difference between the initial and the final states. These populations also determine the total z-component of magnetization of the system. It means that ESR absorption can be measured by magnetization under electromagnetic wave irradiation. This type of ESR is called magnetization detecting ESR: MDESR. We have developed two types MDESR, namely, SQUID-ESR and XMCD-ESR. XMCD is the abbreviation of X-ray Magnetic circular dichroism and is the method to measure magnetization in element and orbital selective manner. SQUID-ESR is easy to conduct by attaching radiation source to a conventional MPMS-SQUID machine. The advantage of SQUID-ESR is the evaluation of absolute value of ESR intensity. While, XMCD-ESR is very sensitive and can detect the magnetization of a few atomic layers. Details of the experimental systems and the test results will be presented. [Preview Abstract] |
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P1.00324: Application of Scanning Probe Nanolithography to fabrication and study of large area graphene and Transition Metal Dichalcogenides heterostructures Rui Dong, Logan Moore, Irma Kuljansihvili Two-dimensional atomic crystals, such as graphene and layered transition metal dichalcogenides (TMDCs), have drawn significant attention because of the unique physical and chemical properties. Recently developed graphene/TMDCs stacking structures provide an attracting solution to design and fabricate unique electronic devices and nanostructures. In this study, we employ the ``direct write'' patterning technique, to fabricate Graphene/TMDCs heterostructures. TMDCs precursor is utilized as an ``ink'' to create the arrays of patterns employing multi-pen AFM cantilevers. The patterned structures of TMDCs precursor on graphene /silicon oxide/silicon in processed in CVD to produce Graphene/TMDCs heterostructures. Raman spectroscopy and AFM characterization demonstrates high quality of as-prepared Graphene/TMDCs nanostructures. Mask free approach significantly reduces contamination of the grahene surface during patterning and demonstrates a promising unconventional technology for fabricating high quality Graphene/TMDCs or other layered nanostructures in a convenient and economical manner with the nanoscale precision. [Preview Abstract] |
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P1.00325: Geometric and Electromagnetic Field Effects on the Excitonic Properties of Core-multishell Semiconductor Quantum Wires Jusciane Silva The effect of eccentricity distortions in the otherwise circular geometry of coremultishell quantum wires on their excitonic transitions is theoretically investigated. Within the effective mass approximation, the Schrödinger equation is numerically solved for electrons and holes in systems with single and double radial heterostructures, whereas the resulting exciton binding energy is calculated by means of a variational approach. Our results demonstrate that for a single shell heterostructure, in-plane electric fields applied in different directions produce qualitatively different energy spectra, which can be used to identify the eccentricity of the system. For a double heterostructure, the eccentricities of the inner and outer shells play an important role on the excitonic binding energy and on the oscillator strength. Our results also show that for a single shell heterostructure with a type-II confinement, i.e. with spatially separated electrons and holes, one of the carriers exhibits either a ring-like or a dot-like energy spectrum, depending on the radius of the system. In this case, a shell-to-core confinement transition for the electron can be induced also by an external magnetic field. [Preview Abstract] |
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P1.00326: Final state lifetime effects in spectroscopic studies of iridium oxide J. Matthias Kahk, David J. Payne Understanding the complex and varied electronic and magnetic properties of late 3rd row transition metal oxides is a topic of significant current interest. The technique of Resonant Inelastic X-ray Scattering (RIXS) is particularly valuable in this field as it provides element- and orbital-specific information about the occupied and unoccupied electronic states. A major advantage of RIXS over techniques such as nonresonant XAS and XES is the sharpening of spectral features due to the absence of a core hole in both the initial and the final states. In typical simulations of RIXS spectra, final state lifetime effects are thus neglected, but this also precludes the possibility to account for the finite lifetime of the excited electron-hole pair created in the RIXS process. Starting from the well-known Kramers-Heisenberg equation, we have developed a new formalism for RIXS simulations which does allow for the inclusion of final state lifetime effects. Results are shown for the O K-edge RIXS of IrO$_{2}$, and the new formalism leads to a vast improvement in the agreement between theory and experiment. A similar approach also yields excellent agreement between theory and experiment for the nonresonant XAS and XES of IrO$_{2}$, as well as the valence band region of the IrO$_{2}$ HAXPES spectrum. [Preview Abstract] |
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P1.00327: Giant Spin Hall Effect in Perpendicularly Magnetized Ta/CoFeB/MgO Structure and Temperature Dependence Qiang Hao, Gang Xiao The Giant Spin Hall Effect (GSHE) in non-magnetic metals with strong spin-orbit coupling (SOC) has been found in various solids like Pt, beta-Ta, and beta-W. The spin current from GSHE solids yields a spin-transfer torque (STT) inside an adjacent ferromagnetic layer with perpendicular magnetic anisotropy (PMA) to effect a magnetization switching. The combination of PMA with STT-induced switching has the advantage of low power consumption, high reliability and durability and data non-volatility over earlier generations of MRAM. Here we first studied the post-annealing effect on achieving PMA in Ta/CoFeB/MgO multilayers. We achieved so far the lowest critical current density of 2.3 MA/cm$^2$ for the STT-induced switching in the presence of 5mT magnetic field as compared to earlier PMA structures. Using a macrospin model, we are able to obtain the Spin Hall Angle of 0.11 in Ta and anisotropy field of 260mT at room temperature, and both values increase with reducing temperature. We also found a scaling law between Ta resistivity and Spin Hall angle in a quadratic relation. Our results are important for magnetic memory and spin-logic applications through optimizing the engineering of such multilayer structures with PMA. [Preview Abstract] |
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P1.00328: Transition to Metallic Phase of Fluid Hydrogen at High Pressure and High Temperature Mari Einaga, Sho Kawaguchi, Katsuya Shimizu, Kenji Ohta, Naohisa Hirao, Yasuo Ohishi We investigated the phase transition to the metallic fluid phase of hydrogen under high pressure and high temperature by the laser heated diamond-anvil cell (LHDAC) up to 100 GPa and 2500 K. Compressed hydrogen was heated by IR laser with a thin gold foil, acts as the laser absorber. The temperature of hydrogen was determined from the thermal radiation spectrum from the gold foil at each laser power. The measured temperature vs. laser power curves showed the maxima at pressures above 80 GPa. These results indicate that the absorptance changed around the gold foil, which may due to a phase transition in hydrogen at the pressure and temperature. We confirmed that no anomaly in the curves was observed without hydrogen. [Preview Abstract] |
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P1.00329: Spin Correlations in Quantum Wires Chen Sun, Valery Pokrovsky We consider theoretically spin correlations in an 1D quantum wire with Rashba-Dresselhaus spin-orbit interaction (RDI). The correlations of non-interacting electrons display electron-spin resonance at a frequency proportional to the RDI coupling. Interacting electrons on varying the direction of external magnetic field transit from the state of Luttinger liquid (LL) to the spin density wave (SDW) state. We show that the two-time total spin correlations of these states are significantly different. In the LL the projection of total spin to the direction of the RDI induced field is conserved and the corresponding correlator is equal to zero. The correlators of two components perpendicular to the RDI field display a sharp ESR driven by RDI induced intrinsic field. In contrast, in the SDW state the longitudinal projection of spin dominates, whereas the transverse components are suppressed. This prediction indicates a simple way for experimental diagnostic of the SDW in a quantum wire. [Preview Abstract] |
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P1.00330: Few-layer-thin Two-dimensional Metallic Niobium Disulfide Nanosheets: Preparation, Optical Characterization and Transport Properties Sihan Zhao, Takato Hotta, Takumi Sawazaki, Mitsuhiro Okada, Hisanori Shinohara, Ryo Kitaura The semiconducting two-dimensional (2D) transition-metal dichalcogenides (TMDs), such as MoS2, WS2 etc., have recently attracted tremendous research attention in the field of materials science. On the other hand, research work on 2D metallic TMDs, such as NbS2, NbSe2 etc., which show superconductivity and charge-density-wave (CDW) states in bulk, has been limited primarily due to the inaccessibility to ultrathin high quality samples. In this contribution, we report a direct chemical vapor deposition (CVD) growth of ultrathin 3R-NbS2 nanosheets down to 3 layers on the exfoliated hexagonal boron nitride (hBN) flakes. AFM data show that most of NbS2 samples grown are very thin with an average lateral size of ca. 2~3 µm. Detailed Raman spectroscopy studies on layer number-identified NbS2 samples reveal a systematic shift of out-of-plane vibration mode (A1g), which offers a reliable and rapid optical method for layer number identification. Two-terminal devices on thin-layered NbS2 were also fabricated and show a metallic transport behavior as predicted by DFT calculations. The metallic nature of thin-layered NbS2 has also been supported by absence of PL peaks regardless of number of layers. Exploration of 2D superconductivity and CDW states in this system is an on-going work. [Preview Abstract] |
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P1.00331: A New Carbon Phase Constructed by Long-Range Ordered Carbon Clusters form Compressing C$_{70}$ Solvates Wen Cui, Mingguang Yao, Shijie Liu, Fengxian Ma, Quanjun Li, Ran Liu, Bo Liu, Bo Zou, Tian Cui, Bingbing Liu A novel carbon material has been recently reported from compressing C$_{60}$ solvates (C$_{60}$/m-xylene) and the obtained high pressure phase--the ordered amorphous carbon cluster (OACC) structure, breaks our inherent understanding of the categorization of various phases and adds a new member to the list of structures [L. Wang et al, Science 337, 825 (2012)]. Our study reveals that m-xylene plays an important role in both the structure and property of the formed novel phase [MG. Yao et al, App Phys Lett 103, 071913 (2013)]. Here, another example of OACC is also presented from compressing C$_{70}$ / m-xylene in which amorphized and highly compressed C$_{70}$ units act as building blocks. The high pressure phase is exceptional incompressible, which can indent the (100) face of diamond. A new phase transition occurs in the compression process, which is very different from compressing C$_{60}$/m-xylene, indicating OACC structure can be tuned by changing the initial fullerene molecules. The deformation of fullerene molecules under pressure and the formation mechanism of the high pressure hard phase have also been revealed in this study. Our study extends the OACC structure to larger fullerenes and suggests a universal rule for the high pressure behaviors of lower symmetry systems of solvated fullerenes [W. Cui et al, Adv Mater 26, 7257(2014)]. [Preview Abstract] |
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P1.00332: Optical properties of highly-extended, ultrathin graphene nanoribbons in carbon nanotubes Hong En Lim, Yasumitsu Miyata, Miho Fujihara, Susumu Okada, Haruka Omachi, Ryo Kitaura, Hisanori Shinohara Growing graphene nanoribbons (GNRs) inside the carbon nanotubes (CNTs) [1, 2] is tempting, as it provides opportunities to tune the width and edge structure of the ribbons synthesized. To have a better insight into their intrinsic properties, it is therefore necessary to study the GNRs in such a confined state. Herein, we report the optical properties of the coronene-derived GNRs, confined in single-wall CNTs of 1.4-1.6 nm. The electronic structures of the outer CNTs were modified using diazonium chemistry [3], allowing clear absorption signals of the inner GNRs to be detected. The absorption bands around 1.5 and 3.4 eV can be related to the first and second transitions between the energy gaps of the valence and conduction bands, in qualitative agreement with the first principle calculations. Our study deepens the understanding on the ribbons fabricated, providing access towards the interesting physics of confined one-dimensional materials. References: [1] H. E. Lim et al. Nat. Commun. 2013, 4, 2548. [2] M. Fujihara et al. J. Phys. Chem. C 2012, 116, 15141-15145. [3] M. S. Strano et al. Science 2003, 301, 1519-1522. [Preview Abstract] |
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P1.00333: Growth and Optical Properties of High-Quality WS$_{2}$ Monolayers on Graphite Yasumitsu Miyata, Yu Kobayashi, Shogo Sasaki, Shohei Mori, Yutaka Maniwa, Kenji Watanabe, Takashi Taniguchi, Hiroki Hibino Atomic-layer transition metal dichalcogenides (TMDCs) have attracted appreciable interest due to their tunable bandgap, spin-valley physics, and potential device applications. However, the quality of TMDC samples available still poses serious problems, such as inhomogeneous lattice strain, charge doping, and structural defects. Here, we report on the growth of high-quality, monolayer WS$_{2}$ onto exfoliated graphite by high-temperature chemical vapor deposition (CVD). Monolayer WS$_{2}$ single crystals grown presents a uniform, single excitonic photoluminescence peak with a Lorentzian profile and a very small full-width at half maximum of 21 meV at room temperature and 8 meV at 79 K. Furthermore, in these samples, no additional peaks are observed for charged and/or bound excitons, even at low temperature. These optical responses are completely different from the results of previously reported TMDCs obtained by mechanical exfoliation and CVD. Our findings indicate that the combination of high-temperature CVD with cleaved graphite surface is an ideal condition for the growth of high-quality TMDCs, and such samples will be essential for revealing intrinsic physical properties and for future applications. [Preview Abstract] |
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P1.00334: Energy landscape scheme for an intuitive understanding of complex domain dynamics in ferroelectric thin films Jong-Gul Yoon, T.H. Kim, W.K. Park, S.M. Yang, S.Y. Jang, T. Min, J.-S. Chung, S.H. Baek, C.B. Eom, T.W. Noh Fundamental understanding of domain dynamics in ferroic materials has been a longstanding issue because of its relevance to many systems and to the design of nanoscale domain-wall devices. Despite many theoretical and experimental studies, a full understanding of domain dynamics yet remains elusive due to complex interactions between domain-walls and disorder. In this work, by observing domain-wall breathing motion in ferroelectric BiFeO$_{3}$ thin film using stroboscopic piezoresponse force microscopy, we demonstrate domain-shape-preserving deterministic domain-wall motion, confirming microscopic return point memory. We also map a spatial energy landscape that provides new insights into domain dynamics. The evolution of complex domain structure can be understood by the process of occupying the lowest available energy states of polarization in the energy landscape which is determined by defect-induced internal fields. [Preview Abstract] |
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P1.00335: Selective formation of zigzag-edges in graphene cracks Miho Fujihara, Ryosuke Inoue, Yutaka Maniwa, Hisanori Shinohara, Yasumitsu Miyata Graphene edges have attracted much attention due to their unique electrical and magnetic properties. To understand these properties, it is highly desired to prepare clean, smooth, and structure-controlled edges. However, structure selective preparation of zigzag or armchair edges has not been achieved yet. Here, we report the selective formation of graphene edges aligned in the zigzag orientation by cleavage with thermally-assisted tensile stress. Graphene grains were grown from methane on copper foil by using chemical vapor deposition. After cooling to room temperature, we occasionally observed zigzag-shaped cracks in graphene. Considering the grain edges which have the zigzag face, these cracks are found to propagate parallel to the zigzag edges. The origin of tension is probably due to the non-uniform lattice strain of graphene induced by thermal shrinking of Cu substrates as supported by Raman strain mapping. Furthermore, we demonstrate the carrier tuning around graphene edges by applying the electric field to the cracks. Our findings pave the way for the fabrication and applications of smooth, long zigzag edges of graphene and other two dimensional materials. [Preview Abstract] |
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P1.00336: Thrust generation of thickness-varying flexible fins Yuanda Li, Peter Yeh, Alexander Alexeev We use three dimensional computer simulations to probe the hydrodynamics and thrust generation of an oscillating flexible fin with varying thickness. The fin is modeled as an elastic rectangular plate that plunges at its leading edge and is submerged in a viscous fluid. Since we assume that the thickest part of the fin is very small compared to its length and width, the plate is modeled as infinitely thin. We introduce an appropriate mass gradient and stiffness gradient in the plate to simulate the effects of the thickness gradient. As the fin flaps, fluid is displaced backwards and a net thrust is generated. We characterize this thrust generation as a function of driving frequency and find optimal conditions for largest propulsion. These findings are useful for designing biomimetic underwater propulsion devices. [Preview Abstract] |
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P1.00337: Precise Analysis of Perfect Zero-Birefringence Polymer Yuki Okada, Osamu Urakawa, Tadashi Inoue Control of strain-induced birefringence of amorphous polymers is an important issue for their optical applications. It is widely accepted that strain-induced birefringence of amorphous polymers has two origins, segment orientation and glassy deformation. The intrinsic birefringence, $\Delta n_{0}$ and the photoelastic coefficient, $C_{\mathrm{d}}$, are indexes of the two origins, respectively. $\Delta n_{0}-C_{\mathrm{d}}$ map help us to predict strain-induced birefringence of copolymers. Perfect zero-birefringence polymers, PZP, means $\Delta n_{0} =$ 0 and $C_{\mathrm{d}} =$ 0. One of the method to obtain the PZP is random copolymerization of three kinds of monomers. In a three components system, the birefringence of copolymers can be characterized by a point inside of the triangle region formed by three points for homopolymers of the three monomers in $\Delta n_{0}-C_{\mathrm{d}}$ map. In this study, PZP of MMA (Methyl methacrylate), TFEMA (Trifluoroethyl methacrylate) and BzMA (Benzyl methacrylate) was synthesized and its birefringence behavior was analyzed. Following the reported composition, we synthesized PZP and conducted dynamic birefringence measurement. $\Delta n_{0}$ value of the synthesized PZP was unexpectedly large at high temperatures because $\Delta n_{0}$ of PMMA and PBzMA showed temperature dependence. More importantly, we found that zero birefringence of PZP is achieved only at a certain temperature. We will also discuss effect of sub relaxations in the talk. [Preview Abstract] |
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P1.00338: Chaos and Big-Bang singularity in Bianchi type-IX universe for the Einstein equation Yuya Takeuchi, Tomio Petrosky, Linda Reichl, Satoshi Tanaka Chaotic dynamics of a spatially homogenous and anisotropic case in the Bianchi type-IX universe model for the Einstein equation has been studied for the vacuum case. There is a hyperbolic fixed point and a separatrix only for the type-IX model with positive cosmological constant. A difficulty in numerical analysis due to the Big-Bang singularity is avoided by constructing an analytical solution near the singular point. Thanks to the local analytic solution and by combining it with global numerical solution, we are able to construct Poincaré’s surface of a section near the separatrix. A new type of chaotic motion characteristics to the Einstein equation will be discussed. [Preview Abstract] |
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P1.00339: NMR Spin-Lattice Relaxation Time T1 of Thin Films Obtained by Magnetic Resonance Force Microscopy Sungmin Kwon, Seung-bo Saun, Soonchil Lee, Soonho Won NMR spectrum and spin-lattice relaxation time(T1) of CaF2 thin film samples deposited on a silicon cantilever tip were obtained by magnetic resonance force microscopy(MRFM). Thickness of the thin films were 50nm and 150nm. In order to measure T1, a cyclic adiabatic inversion method was used with periodic phase inversion. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental conditions such as temperature and magnetic field. [Preview Abstract] |
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P1.00340: Computational and Physical Analysis of Catalytic Compounds Richard Wu, Jung Jae Sohn, Richard Kyung Nanoparticles exhibit unique physical and chemical properties depending on their geometrical properties. For this reason, synthesis of nanoparticles with controlled shape and size is important to use their unique properties. Catalyst supports are usually made of high-surface-area porous oxides or carbon nanomaterials. These support materials stabilize metal catalysts against sintering at high reaction temperatures. Many studies have demonstrated large enhancements of catalytic behavior due to the role of the oxide-metal interface. In this paper, the catalyzing ability of supported nano metal oxides, such as silicon oxide and titanium oxide compounds as catalysts have been analyzed using computational chemistry method. Computational programs such as Gamess and Chemcraft has been used in an effort to compute the efficiencies of catalytic compounds, and bonding energy changes during the optimization convergence. The result illustrates how the metal oxides~stabilize and the steps that it takes. The graph of the energy computation step(N) versus energy(kcal/mol) curve shows that the energy of the titania converges faster at the 7th iteration calculation, whereas the silica converges at the 9th iteration calculation. [Preview Abstract] |
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P1.00341: Superconductivity in Opal-based superconducting nanocomposites M.K. Lee, E.V Charnaya, L.J. Chang, Yu. A. Kumzerov, M.F. Lin In this study, we investigate superconducting nanocomposites (SCNCs) to elucidate superconductivity in nanostructured type I superconductor. In, Sn and Hg are loaded into opal matrices by high pressure up to 10kbar, in which introducing superconducting metals into templates preserves their own 3D nanostructures. The opal matrices is adopted because it is a well-developed nanoconfinement and widely used in the studies of photonic crystal due to its periodically-superlatticed nanoporous structure. The SCNCs are then measured by Quantum Design MPMS 3 under different external magnetic fields reveal the field dependences of Tc and irreversibility temperature (Tirr). Next, AC susceptibility measurements of SCNCs determine grain coupling, vortex dynamics and field dependence of activation barrier (Ua) as well as Tc. Additionally, the phase diagrams of these SCNCs are analyzed to study superconductivity for a system with similar nanogeometry. Exotic phase diagrams in the opal SCNC studies reveal an enhanced upper critical field (Hc2 (0)) and curvature crossover of upper critical field line. Additionally, according to the field dependence of Ua(H), curvature crossover of the upper critical field line can occur, owing to vortex phase transition. [Preview Abstract] |
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P1.00342: The physics of a cell doublet: a minimal system to study early embryo morphogenesis Herve Turlier, Jean-Leon Maitre, Takashi Hiiragi, Francois Nedelec In early embryos, the shape of cells is determined in part by the actomyosin cortex and in part by interactions with the surrounding environment. Cell-cell adhesion, in particular, is determinant for the overall embryo organization. This complex interplay between cell autonomous mechanical properties and cell-cell interactions can advantageously be analyzed in pairs of isolated cells. We study theoretically and experimentally shape changes in doublets of mouse embryo blastomeres. Simple scaling analysis and numerical simulations can predict the various configurations adopted by blastomere doublets over different stages of embryo development. Our study provides a simple and robust physical framework to understand and characterize quantitatively diverse morphogenetic events such as compaction, entosis and cell internalization. [Preview Abstract] |
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P1.00343: Calculation of modal contributions to thermal transport across Si/Ge and In$_{0.53}$Ga$_{0.47}$As/InP interfaces Kiarash Gordiz, Asegun Henry Reliable and quantitative calculation of the conductance of different phonons across an interface can have a significant impact on the applications where thermal interface resistance is limiting and can aid in the rational design of thermal interface materials. A new formalism for extracting the modal contributions to thermal interface conductance with full inclusion of temperature dependent anharmonicity and all of the atom level topography is presented. Application of the formalism to Si/Ge and In$_{0.53}$Ga$_{0.47}$As/InP interfaces reveals fundamental information on the nature of the vibrational modes involved in heat transfer and the interactions/correlations among them. Four distinct classes of vibrational modes are detected for the two interfaces. For Si/Ge interface, the density of states for these vibrational classes are completely mixed, while surprisingly for In$_{0.53}$Ga$_{0.47}$As/InP interface they are completely segregated. For Si/Ge interface, interfacial modes, located around 12THz, contribute near 20{\%} to the total conductance, while for In$_{0.53}$Ga$_{0.47}$As/InP interface, low frequency extended modes contribute more than 50{\%} to the total conductance, which is even larger than the maximum predicted contribution by phonon gas model. Temperature dependent anharmonicity analysis shows that increasing temperature decreases the contribution by extended modes and increases the contribution by partially extended modes. In both of the interfaces, Interfacial modes exhibit the maximum per mode contribution. [Preview Abstract] |
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P1.00344: Coherence lengths in attractively interacting Fermi gases with spin-orbit coupling Yu Yixiang, Jinwu Ye, Wuming Liu Extensive research has been lavished on the effects of spin-orbit couplings (SOCs) in attractively interacting Fermi systems in both neutral cold-atom systems and condensed-matter systems. Recently, it was suggested that a SOC drives a class of BCS to Bose-Einstein condensate (BEC) crossover that is different from the conventional one without a SOC. Here, we explore what are the most relevant physical quantities to describe such a BCS to BEC crossover and their experimental detections. We extend the concepts of the coherence length and ?Cooper-pair size? in the absence of SOC to Fermi systems with SOC. We investigate the dependence of chemical potential, coherence length, and Cooper-pair size on the SOC strength and the scattering length at three dimensions (3D) (the bound-state energy at 2D) for three attractively interacting Fermi gases with 3D Rashba, 3D Weyl, and 2D Rashba SOC, respectively. We show that only the coherence length can be used to characterize this BCS to BEC crossover. Furthermore, it is the only length which can be directly measured by radio-frequency dissociation spectra type of experiments. We stress crucial differences among the coherence length, Cooper-pair size, and the two-body bound-state size. Our results provide the fundamental and global picture of the BCS to BEC crossover and its experimental detections in various cold-atom and condensed-matter systems. [Preview Abstract] |
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P1.00345: Theory of Luminescent Emission in a Nanocrystal Doped by Co$^{2+}$ George Chappell, Que Huong Nguyen We theoretically study the effect on the electronic structures and optical properties of a Co-doped semiconductor nanocrystal (NC) of the interaction between the impurity atom and an electron existing inside the NC. The optical properties of impurity centers in NCs are very different from the bulk cases. Beside the strong hybridization of $s$-$p $electrons of the semiconductor host and $d $electrons of the impurity due to confinement and the modification of the crystal field near the surface of the NCs, the Coulomb and exchange interaction of the d-electrons of the impurity centers with the confined electrons (or holes) existing inside the NCs could change the photoluminescence properties. In the strong confinement approximation, the boundary conditions enhance the coupling, and the effect on photoluminescence could be large. The transition $^{4}$T$_{1}-^{2}$E of Co$^{2+}$ has been considered. The exchange interaction between the extra electron and the states of the impurity ion together with the confinement effect mix the wave functions, split the impurity energy levels, break the previous selection rules, and change the transition probabilities. Energy, wave functions, luminescence efficiency, and transition lifetime have been calculated. The results imply that the PL intensity increases and the lifetime is shortened inside the NC. [Preview Abstract] |
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P1.00346: Role of precursor crystal structure on electrochemical performance of carbide-derived carbon electrodes Benjamin Palazzo, Zach Norris, Greg Taylor, Lei Yu, Samuel Lofland, Jeffrey Hettinger Binary carbides with hexagonal and cubic crystal structures have been synthesized by reactive magnetron sputtering of vanadium and other transition metals in acetylene or methane gas mixed with argon. The binary carbides are converted to carbide-derived carbon (CDC) films using chlorine gas in a post-deposition process in an external vacuum reaction furnace. Residual chlorine has been removed using an annealing step in a hydrogen atmosphere. The CDC materials have been characterized by x-ray diffraction, x-ray fluorescence, and scanning electron microscopy. The performance of the CDC materials in electrochemical device applications has been measured with the hexagonal phase precursor demonstrating a significantly higher specific capacitance in comparison to that of the cubic phase. We report these results and pore-size distributions of these and similar materials. [Preview Abstract] |
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P1.00347: Stabilizing the false vacuum: Mott skyrmions M\'arton Kan\'asz-Nagy, Bal\'azs D\'ora, Eugene Demler, Gergely Zar\'and Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons have been observed in many areas of physics, their intriguing higher dimensional topological relatives, skyrmions remained mostly elusive. In particular, earlier attempts to create stable individual skyrmions in ultracold atomic experiments suffered from important instabilities: skyrmions have a tendency to shrink or expand, and to slip away from the atomic trap. In this work, we propose that loading a three-component nematic superfluid, such as $^{23}$Na, into a deep optical lattice and thereby creating an insulating core, one can create topologically stable individual skyrmions, and investigate their properties in detail. Furthermore, the spectrum of the excitations of the superfluid and their quantum numbers change dramatically in the presence of the skyrmion, and they reflect the presence of a trapped monopole, as imposed by the skyrmion's topology.\\[4pt] M. Kan\'asz-Nagy, B. D\'ora, E. A. Demler, G. Zar\'and, \textit{Sci. Rep.} \textbf{5,} 7962 (2015). [Preview Abstract] |
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P1.00348: In Silico Discovery of High Deliverable Capacity Metal-Organic Frameworks Yi Bao, Richard Martin, Cory Simon, Maciej Haranczyk, Berend Smit, Michael Deem Metal organic frameworks (MOFs) are actively being explored as potential adsorbed natural gas storage materials for small vehicles. Experimental exploration of potential materials is limited by the throughput of synthetic chemistry. We here describe a computational methodology to complement and guide these experimental efforts. The method uses known chemical transformations \emph{in silico} to identify MOFs with high methane deliverable capacity. The procedure explicitly considers synthesizability with geometric requirements on organic linkers. We efficiently search the composition and conformation space of organic linkers for nine MOF networks, finding 48 materials with higher predicted deliverable capacity (at 65 bar storage, 5.8 bar depletion, and 298 K) than MOF-5 in four of the nine networks. The best material has a predicted deliverable capacity 8\% higher than that of MOF-5. [Preview Abstract] |
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P1.00349: Many-body calculation for charge transport through triangular quantum dot molecules Chih-Chieh Chen, Yia-chung Chang, David M.T. Kuo We study the many-body effect of electron tunneling through the coupled quantum dots systems in the Coulomb blockade regime. Using the equation of motion method for the non-equilibrium Green's function, we calculate the charge current and conductance of junctions consisting of metallic electrodes and a few quantum dots. Many-particle correlation functions are explicitly solved numerically. Quantum phenomena like quantum interference, Coulomb blockade and spin blockade for the triangular quantum dot molecules are discussed. Our work suggests a new method for the modeling of the mesoscopic transport. [Preview Abstract] |
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P1.00350: Confinement of metal nanoparticles with various sizes in silica matrices Jeeun Lee, Shin-Hyun Kang, Sung-Min Choi Many studies have been focused on metal nanoparticles since they have interesting properties due to their high surface area to volume ratio. While bulk metals have constant properties regardless of their sizes, the noble properties of metal nanoparticles such as catalytic activity, magnetic, and electronic properties dramatically change depending on their sizes. Here, metal nanoparticles with various sizes are synthesized, functionalized, then confined in stable silica matrices and their physical and chemical properties are investigated. The structure of each system is characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). [Preview Abstract] |
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P1.00351: Fitness, environmental changes and the growth of modularity- a quasispecies theory for the evolutionary dynamics of modularity Liang Niestemski, Jeong-Man Park, Michael Deem Although the modularity of a biological system is demonstrated and recognized, the evolution of the modularity is not well understood. We here present a quasispecies theory for the evolutionary dynamics of modularity. Complemented with numerical models, this analytical theory shows the calculation of the steady-state fitness in a randomly changing environment, the relationship between rate of environmental changes and rate of growth of modularity, as well as a principle of least action for the evolved modularity at steady state. [Preview Abstract] |
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P1.00352: Pressure dependence of the nematic spin correlations in detwinned BaFe$_{1.97}$Ni$_{0.03}$As$_{2}$ Wenliang Zhang, Xingye Lu, Jitae Park, Pengcheng Dai In the paramagnetic tetragonal phase of BaFe$_{\mathrm{2-x}}$Ni$_{\mathrm{x}}$As$_{2}$, inelastic neutron scattering shows a spin excitation anisotropy emerges at a temperature well above the structure transition temperature ($T_{\mathrm{s}})$ [1], consistent with the onset of in-plane resistivity anisotropy [2]. However, how the applied uniaxial strain, which artificially breaks the four-fold symmetry, influences the observed anisotropy is still unclear. Here we studied the pressure dependence of the nematic spin correlations in detwinned BaFe$_{1.97}$Ni$_{0.03}$As$_{2}$. We find that the spin excitation anisotropy temperature ($T^{\ast})$ is largely enhanced when changing the pressure from a mediate level ($\sim$ 8MPa) to a high level ($\sim$ 15MPa) [3]. Our results suggest the $T^{\ast}$ may be not a characteristic temperature where the system transit to a nematic phase, but a temperature the nematic fluctuations can reach under a uniaxial stress.\\[4pt] [1] Xingye Lu et al., Science 345, 657-660 (2014)\\[0pt] [2] J. H. Chu et al., Science 329, 824-826 (2010)\\[0pt] [3] Wenliang Zhang et al., unpublished manuscript (2015). [Preview Abstract] |
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P1.00353: Evolution of sparsity and modularity in a model of living matter Mathieu Hemery, Olivier Rivoire How much of the sequence of a protein accounts for its current function and how much is the result of its past evolutionary history? Being the product of a long evolutionary process in an ever changing environment, the sequence of current natural proteins may retain the trace of prior selected functions. Or more simply, it may contain elements that are not -- or no more -- subject to selection. Using a simple physical model previously analysed to study the folding problem, we probe the influence of past evolutionary environments on protein sequences. Simulations of evolutionary dynamics generically lead to non-trivial correlations between temporal fluctuations and geometrical structure, illuminating the link between history, geometry and function. [Preview Abstract] |
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P1.00354: Supramolecular Polymer Nanocomposites -- Improvement of Mechanical Properties Jesse Hinricher, Colin Neikirk, Rodney Priestley Supramolecular polymers differ from traditional polymers in that their repeat units are connected by hydrogen bonds that can reversibly break and form under various stimuli. They can be more easily recycled than conventional materials, and their highly temperature dependent viscosities result in reduced energy consumption and processing costs. Furthermore, judicious selection of supramolecular polymer architecture and functionality allows the design of advanced materials including shape memory and self-healing materials. Supramolecular polymers have yet to see widespread use because they can't support much weight due to their inherent mechanical weakness. In order to address this issue, the mechanical strength of supramolecular polymer nanocomposites based on ureidopyrmidinone (UPy) telechelic poly(caprolactone) doped with surface activated silica nanoparticles was investigated by tensile testing and dynamic mechanical analysis. The effects of varying amounts and types of nanofiller surface functionality were investigated to glean insight into the contributions of filler-filler and filler-matrix interactions to mechanical reinforcement in supramolecular polymer nanocomposites. [Preview Abstract] |
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P1.00355: Slip and flow dynamics of polydisperse thin polystyrene films. Seyed Mostafa Sabzevari, Joshua D. McGraw, Karin Jacobs, Paula M. Wood-adams We investigate the slip of binary and ternary mixtures of nearly monodisperse polystyrene samples on Teflon-coated (AF2400) silicon wafers using dewetting experiments. Binary mixtures of long and short chains along with ternary mixtures with a fixed weight-average molecular weight Mw but different number-average molecular weight Mn were prepared. Thin films of ca. 200 nm were spin coated on mica from polymer solutions and transferred to Teflon substrates. Above the glass transition temperature Tg the films break up via nucleation and growth of holes. The hole growth rate and rim morphology are monitored as a function of Mn and annealing protocol of the films before transfer to Teflon substrates. Slip properties, accessed using hydrodynamic models, and flow dynamics are then examined and compared. We found that the rim morphology and slip of polystyrene blends on Teflon depends on the molecular weight distribution. Similarly, flow dynamics is affected by the presence of short chains in mixture. Moreover, we can provoke differences in slip by choosing appropriate annealing and film transfer protocols for PS films that have first been spin cast on mica surfaces. [Preview Abstract] |
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P1.00356: Particle-Laden Leidenfrost Droplets: Final-Stage Observations Zecong Fang, Jie Xu Little interest has been paid to the final stage of a Leidenfrost droplet until a recent study by Celestini et al [Phys. Rev. Lett. 109, 034501 (2012)] reporting an unexpected take-off phenomenon of micrometer sized pure liquid droplets ($R_{l} |
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P1.00357: Carbon Nanotubes Synthesis Through Gamma Radiation Pablo Tirado, Rafael Garcia, Jorge Montes, Rodrigo Melendrez, Marcelino Barboza, Oscar Contreras Carbon nanotubes show a great potential of applications since there discovery by Iijima in 1991$^{\mathrm{[1]}}$ due to their numerous physical-chemical properties such as their high weight to strength relationship, which make them ideal to use in high resistance compound materials, and in many other applications$^{\mathrm{[2]}}$ In this work, a novel method for the synthesis of carbon nanotubes is presented, starting from an ultra-thin sheet of graphite synthesized by the chemical vapor decomposition technique (CVD), using ultra high purity methane and hydrogen at 1200$^{\circ}$C in a horizontal quartz reactor. For the synthesis of carbon nanotubes, the graphite sheets were exposed to different doses of radiation, with the objective of breaking the graphite bonds and form carbon nanotubes; a Gammacell equipment model 220 Excel was used for the purpose, which counts with a radiation source of cobalt 60, and a current radiation rate of 0.9 Gy/seconds. The time of exposure to radiation was varied in each sample, according to the desired dose of radiation in each case, afterwards the samples were characterized using the Raman spectroscopy and TEM microscopy techniques with the objective of observing the kind of nanotubes formed, their morphology and their number of defects. Results will be shown during the poster session. [Preview Abstract] |
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P1.00358: Hydration Layer of Enzymes Partially Controls Conformational Dynamics Zahra Alavi For a typical (20 kD, 4 nm size) monomeric enzyme, more than 50{\%} of the residues are at the surface. The mechanics of these soft, heterogeneous nanoparticles was recently shown to be viscoelastic. Here we explore the contribution of the enzyme's surface to the mechanics of the molecule. Nano-rheology provides sub-?angstrom resolution measurements of the reversible deformation of the enzyme subject to an oscillatory mechanical stress. We perturb the surface of the enzyme by adding small amounts of DMSO, believed to affect ordering of the enzyme - water interface. We observe a dramatic though reversible change in the mechanics of the enzyme, which becomes more viscous. On the other hand, the catalytic speed is unaffected, while at higher DMSO concentrations (\textgreater 1 {\%}) it even increases. Our measurements show that small (\textless 1 {\%}) bulk concentrations of DMSO, which have negligible effect on the physico-chemical properties of bulk water, including the viscosity and dielectric constant, have nonetheless dramatic effect on the dynamics of the hydration layer of the enzyme, and ultimately on the enzyme's mechanics. DMSO accumulates in the hydration layer (``binds to the surface of the enzyme''). Apparently the order - inducing (``kosmotropic'') quality of DMSO leads to a hardening of the enzyme - water interface. [Preview Abstract] |
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P1.00359: Effect of monomer sequence distribution in poly(vinyl alcohol-\textit{co}-vinyl acetate) on the hydrogen bonding structure and physical properties Shun Tasaka, Osamu Urakawa, Tadashi Inoue It has been well known that hydrogen (H-) bonding interaction in polymer materials strongly affects their properties. For example, glass transition temperature ($T_{\mathrm{g}})$ and terminal relaxation time increase by introducing H-bonding sites. This is because the molecular motion is restricted due to the formation of inter- and intra-chain H-bonds. For H-bonding copolymers in which H-bonding monomer and non- bonding one are incorporated, the fraction dependence of their properties has been examined so far. However, the influence of sequence distribution on their properties has not been studied in detail. In this work, we investigated the H-bonding structure and physical properties of molten poly(vinyl alcohol-\textit{co}-vinyl acetate) with different monomer sequences to clarify the effect of the sequence distribution. We found that, with increasing the randomness in monomer sequences, the number of H-bonds between carbonyl group and hydroxyl (OH) group increased. Moreover, OH groups form linearly connected structure (OH-OH-OH) and its number also increases with the sequence randomness. $T_{\mathrm{g}}$ for the samples with higher sequence randomness are higher than those with lower randomness for high VOH copolymers. These results indicate that formation of larger number of H-bonds makes $T_{\mathrm{g}}$ higher. [Preview Abstract] |
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P1.00360: Quantum Behavior of an Autonomous Maxwell Demon Adrian Chapman, Akimasa Miyake A Maxwell Demon is an agent that can exploit knowledge of a system's microstate to perform useful work. The second law of thermodynamics is only recovered upon taking into account the work required to irreversibly update the demon's memory, bringing information theoretic concepts into a thermodynamic framework. Recently, there has been interest in modeling a classical Maxwell demon as an autonomous physical system to study this information-work tradeoff explicitly. Motivated by the idea that states with non-local entanglement structure can be used as a computational resource, we ask whether these states have thermodynamic resource quality as well by generalizing a particular classical autonomous Maxwell demon to the quantum regime. We treat the full quantum description using a matrix product operator formalism, which allows us to handle quantum and classical correlations in a unified framework. Applying this, together with techniques from statistical mechanics, we are able to approximate nonlocal quantities such as the erasure performed on the demon's memory register when correlations are present. Finally, we examine how the demon may use these correlations as a resource to outperform its classical counterpart. [Preview Abstract] |
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