Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K55: Advancing Polymer Physics by Integrating Simulation and Theory III: Self-Assembly and Charged PolymersFocus
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Sponsoring Units: DPOLY DCOMP Chair: Charles Sing, University of Illinois at Urbana–Champaign Room: LACC 515A |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K55.00001: Abstract Withdrawn Invited Speaker:
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Wednesday, March 7, 2018 8:36AM - 8:48AM |
K55.00002: Effect of Ion Content on Adhesion of Ionomers from Molecular Dynamics Simulations Janani Sampath, Patrick Murtha, Lisa Hall Ionomers are polymers that contain a small amount of charged groups attached to a non-polar backbone, used in packaging and other applications. We consider a dense melt of ionomers and their counterions without solvent, in which aggregation of ions significantly impacts material properties. We use a coarse-grained model that includes uncharged backbone monomers, charged pendants and counterions, and sticker groups that represent unneutralized acid groups (similar to uncharged monomers but placed pendant to the backbone and with additional cohesive interactions with themselves and ionic groups). To understand interfacial behavior of ionic aggregates, we simulate a freestanding ionomer film thick enough to reach approximately bulk behavior in the center of the film. We find that aggregates are depleted near the interface, in agreement with prior experimental results. Density profiles indicate a pronounced layering of ionic aggregates close to the interface. To study adhesion, we analyze ionic aggregate and polymer backbone behavior after two surfaces are brought together; effects of pendant group mole fraction and neutralization level will be discussed. |
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K55.00003: Correlation and Association Effects of Ions in Block Copolymers from Fluids Density Functional Theory Jonathan Brown, Lisa Hall Ion containing block copolymers have potential application as solid-state, nonflammable battery electrolytes and in other charge transport applications, such as electroactive actuators. In these systems, ion clustering and preferential solvation into the microphase with the higher dielectric constant strongly affect on the polymer phase behavior; even a small amount of salt can significantly increase the effective segregation strength between the blocks. Additionally, Lithium ions can strongly complex with the ether Oxygens (EO) in polymers such as polyethylene oxide. To model these effects, we implement a coarse-grained model using fluids density functional theory. Ion correlations are introduced using the direct correlation function of a reference fluid of unbonded monomers and salt, obtained by solving the Ornstein-Zernike equation with the hypernetted-chain closure, and Li-EO complexation is modeled using an extension of the inhomogeneous statistical associating fluid theory (iSAFT). By turning these individual effects on and off, we show how each contributes to the phase behavior of these polymer systems. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K55.00004: Kinetics of conformational changes in polyelectrolyte systems Arindam Kundagrami, Swati Sen, Soumik Mitra Interest in the kinetics of conformational changes in polyelectrolyte systems, unlike their equilibrium phase behavior, has been sporadic, but has received recent attention given their relevance to biological problems like protein-folding or biomedical processes like drug-delivery. Our group has been working on studying the time-dependent, inhomogeneous profiles of physical variables, such as mass and charge densities and osmotic stress, related to such kinetic processes. We will present our understanding that we have developed on this topic over the past two years, especially for two systems - polyelectrolyte gels, and single, isolated, polyelectrolyte chains. Our study considers important issues like charge-regularization and role of elasticity and electrostatics to modulate the spatially varying osmotic forces, which drive these conformational changes. The major results we have obtained include estimation of effective bulk modulus of charged gels, time-dependency of the size of a gel or a single chain as a function of its charge content, temperature, density of cross-links, and chemical affinity of the polymer and the solvent. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K55.00005: Integrating PRISM theory and molecular dynamics simulations for studying assembly in solutions of block copolymers with varying sequences and composition Ivan Lyubimov, Daniel Beltran-Villegas, Arthi Jayaraman In this talk, we will present our recent work using Polymer Reference Interaction Site Model (PRISM) theory and molecular dynamics (MD) simulations to study amphiphilic block copolymers (BCPs) in solution. In both methods, we use a generic coarse-grained model to represent amphiphilic AB BCPs in implicit solvent with the solvophobicity of the B block captured using effective B-B attractions modeled using Lennard Jones potential. We study the assembly in solutions of amphiphilic BCPs as a function of increasing solvophobicity for varying BCP sequences (diblock and triblock) and composition (solvophobic-rich or solvophilic-rich). The comparison of inter-molecular pair correlations, g(r), and structure factors, S(k), shows excellent agreement between PRISM predictions and MD simulations at low solvophobicities. Even though PRISM theory fails to converge to a numerical solution at higher solvophobicities where we see assembled structures in MD simulations, the low solvophobicity results from PRISM predict most of the thermodynamic signatures of the solutions at higher solvophobicities. This shows that PRISM theory could be used to sweep a wide range of design parameters much faster than MD simulations, and predict structure and thermodynamics during assembly in copolymers solutions. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K55.00006: Comparison of Field-Theoretic Approaches in Predicting Polymer Nanocomposite Phase Behavior Amalie Frischknecht, Jason Koski, Robert Ferrier, Jr., Nadia Krook, Huikuan Chao, Russell Composto, Robert Riggleman The considerable parameter space associated with polymer nanocomposites (PNCs) requires efficient theoretical and simulation methods to understand their assembly and guide experiments. We directly compare field-based approaches for modeling PNCs, one equilibrium and one nonequilibrium method. We find that common approximations used in typical equilibrium field-based simulations of PNCs, such as the mean-field approximation or an evenly distributed graft site distribution, have a prominent impact on the large scale phase behavior of polymer nanocomposites in experimentally relevant regimes. The nonequilibrium method trivially circumvents these approximations while also providing analysis of nonequilibrium phenomena. The nonequilibrium method is compared to experiments consisting of polystyrene grafted gold nanorods in a poly(methyl methacrylate) matrix to ensure the model gives results that qualitatively agree with the experiments. Using this insight, we further implement these methods to study a more complex system, examining the brush structure and assembly of mixed brush nanoparticles in solution. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K55.00007: Extended Hybrid Particle-Field Approach for Simulating Polymeric Systems Dong Meng, Jing Zong We present a mesoscale simulation scheme developed based on the hybrid particle-field concept. It is acknowledged that particle- and field-based approaches enjoy distinct however complementary advantages. The former offers fully resolved microscopic details but suffers limited time/length scales when applied to systems of high densities and long-range interactions. The opposite can be generally said about field-based approach. In the proposed hybrid scheme, by decomposing interactions into subcomponents, suitable strategies can be prescribed to combines strengths of both approaches. Specifically, components producing fields of less fluctuations (e.g. pressure-like fields) are treated using a field-theoretic approach, and the ones producing strong correlations and fluctuations are retained in explicit particle forms. Evolution of fields can be simplified by adopting the saddle point values that are consistent with the instantaneous particle configuration, while conventional particle-based methods are used to sample particle coordinates. Fields and particles can be evolved at different rate, resulting a temporary decoupling that can be exploited for parallelized implementations. Several cases of applications will be discussed to illustrate the method’s performance and accuracy. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K55.00008: Simulations of Self-Assembly in Globular Protein-Polymer Conjugates Helen Yao, Bradley Olsen Globular protein-polymer conjugates, a type of block copolymer where one block is a fully-folded globular protein and the other is a synthetic polymer, have been demonstrated to self-assemble into a wide variety of biofunctional nanostructures analogous to those formed by traditional block copolymers. However, the phase behavior of bioconjugates differs dramatically from their better-studied counterparts. Herein, we develop a simple molecular model of the bioconjugates based on a hard sphere colloid (the protein) conjugated to a soft sphere colloid (the polymer). We examine the self-assembly of these dumbbell molecules and investigate the phase behavior of the protein-polymer conjugates using three-dimensional molecular dynamics simulations. This model shows lyotropic self-assembly with increasing concentration, and several different phases can be observed that are analogous to those seen in experiments. Modifying the size of the soft sphere mimics changes in polymer molar mass, while changes in the interaction potentials between different blocks enable exploration of the relative role of polymer-polymer, protein-protein, and protein-polymer interactions in driving self-assembly. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K55.00009: Determination of Globally Stable Block Copolymer Phases Using Particle Swarm Optimization Carol Tsai, Kris Delaney, Glenn Fredrickson The unguided search for the stable phase of a block copolymer of a given composition and architecture is a problem of global optimization with important ramifications from a materials discovery perspective. In this talk, we discuss the development of a reciprocal-space Particle Swarm Optimization (PSO)-SCFT method in which we manipulate the Fourier components of SCFT fields near the principal shell. Effectively, the PSO facilitates the search through a space of reciprocal-space SCFT seeds which yield a variety of morphologies. We present results for applying PSO-SCFT to conformationally symmetric and asymmetric diblock copolymers, and discuss the successes and challenges of the method. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K55.00010: Systematic and Simulation-Free Coarse Graining of Diblock Copolymer Melts YAN WANG, Qiang WANG Since full atomistic simulations of many-chain systems used in experiments are currently not feasible due to their formidable computational requirements, developing coarse-grained (CG) models (potentials) to greatly speed-up molecular simulations of real polymeric systems has attracted great interest. We recently proposed a systematic and simulation-free strategy for coarse graining multi-component polymeric systems [Q. Wang, Polymer 117, 315 (2017)], where we use the well-developed Polymer Reference Interaction Site Model (PRISM) theory, instead of the commonly used many-chain molecular simulations, for both the original and CG systems. Here we apply our strategy to the structure-based coarse graining of diblock copolymer melts, and examine in detail how the CG potentials vary with the coarse-graining level. We show analytically that our structure-based coarse-graining strategy does not change the order-disorder transition of symmetric diblock copolymer melts at the mean-field level. We also show, with highly accurate numerical results, that the CG system cannot reproduce the thermodynamic properties (i.e., the interchain internal energy per chain and virial pressure) of the original system at any coarse-graining level. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K55.00011: Permeability Maximization of Polymer Networks Won Kyu Kim, Matej Kanduč, Rafael Roa, Joachim Dzubiella Permeability measures the ability of a material, such as a polymer network (hydrogel), to transport molecular solvents and solutes and defines an important control parameter in soft functional material applications, e.g., filtration, drug release, and transport of reactants in responsive nanoreactors [1-4]. We calculate permeabilities by means of coarse-grained simulations and theory of a model polymer network. We find that the permeability can be maximized by optimal polymer volume fractions and inter-particle interactions between the polymer and the penetrating solutes. This nontrivial phenomenon is triggered by a competition between solute partitioning [1-3] and diffusion [2]. Throughout a wide range of parameter space of solvent quality, solute coupling, and gel volume fraction, a rich topology of the partitioning is found. The solutes' diffusivity is highly correlated to gel structures, resulting in a drastically nonmonotonous permeability. Possible applications to hydrogel based devices such as responsive nanoreactors for catalysis [2,4] are discussed. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K55.00012: Modeling core-shell particle morphology of engineered polyolefin-acrylic particles for impact modification Jian Yang, Valeriy Ginzburg, Liang Chen, Andy Li, Carlos Cruz, Matthew Carter, Robert Moglia Novel polyolefin-acrylic (POA) core-shell particles derived from polyolefin elastomers are being developed as impact modifiers for engineering plastics. However, good compatibility of POA particles in polymer matrices is critical to achieve desirable impact performance. We computed solubility parameters for the core, shell and matrix materials as a function of their chemical composition and input those values to Self Consistent Field Theory (SCFT) to investigate the role of shell composition and grafting on the particle surface morphology and compatibility of POA particles in the target matrix polymer. A comparison with microscopic images of POA particle core-shell morphology is also presented. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K55.00013: Phase transition path and formation of stable and metastable structures in self-assembled rod-coil block copolymers Ping Tang, Tongjie Sun, Faqiang Liu, Feng Qiu, Yuliang Yang By applying the string method with the self-consistent field theory to the polymeric system with chain rigidity, we aim to develop effective methods to investigate order-order phase transition kinetics, including the minimum energy pathways, the emergence of various metastable states and their dependence on these pathways. By designing different initialization procedures of the "string", we focus on studying the epitaxial relationship between distinct phases, the nucleation details including the shape, size of the critical nucleus and nucleation barrier, and the stability of the metastable states. Furthermore, we develop effective numerical algorithms to deal with chain rigidity. In this way, we expect to realize the design and regulation of the kinetic pathways to complex spherical packing phases, multiply continuous networks and complex mesophases combined with liquid crystal orientation effect. The developed theoretical method is expected to understand the phase transition pathways and kinetics regarding complex self-assembled networks and liquid crystalline phases, thus providing guidance for the design and fabrication of high performace and functional materials. |
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