Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E08: Structure and Dynamics of Charged PolymersFocus Live
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Sponsoring Units: DPOLY DSOFT DCOMP DBIO Chair: Charles Collier, Oak Ridge National Lab; Bradley Lokitz, Oak Ridge National Lab |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E08.00001: Advanced Dielectric Polymeric Materials with Rational Design of Nano-Morphologies Xin Chen, Qiyan Zhang, Tian Zhang, Qiming Zhang Polymer dielectrics are widely used for energy storage in pulsed power systems and for improving the power efficiency such as in hybrid electric vehicles (HEVs) and power grid. Many efforts have been made in materials design and processing to enhance the performance of dielectric polymers for meeting the ever-increasing requirements of reducing the size of devices and systems and emerging applications. In general, dielectric constant, dielectric loss, and breakdown strength comprehensively determine the performance of dielectric capacitors. It is a challenge to acquire desired properties specific to multiple applications by precisely tailoring the polymer structures. In this talk, we will present several strategies to modify the nanostructures for developing polymer dielectrics with outstanding performance. 1) high dielectric response of polymer nanocomposites with tiny amount of nanofillers (< 1vol%) while also enhancing dielectric strength; 2) ultra-high breakdown strength of polymer blends by rational design of interactions between polymer chains. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E08.00002: The nanostructure and ion dynamics of novel hydrocarbon ionene AEMs via scattering and simulation Eric Schibli, Steven Holdcroft, Barbara J Frisken Perfluorinated sulfonic acid-based (PFSA) ionomers currently dominate the fuel cell industry. However, the hostility to catalyst material, difficult and expensive synthetic routes, and environmental concerns of PFSA materials present major challenges to wider adoption of fuel cell technology. Hydrocarbon-based membranes utilize simple, well-developed synthetic routes that allow for rapid material development. We have investigated a promising series of fully aromatic hydrocarbon ionene anion-exchange membranes (AEMs) utilizing a combination of X-ray scattering and molecular dynamics simulations to elucidate the morphology of these materials and have utilized molecular dynamics to investigate the role of cation and polymer architecture in ion transport dynamics. Backbone architecture appears to play a limited role in determining conductivity at constant hydration number. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E08.00003: Charging Dynamics and Structure of Ionic Liquids in Nanoporous Supercapacitors Konrad Breitsprecher, Christian Holm, Svyatoslav Kondrat Ionic liquid based nanoporous supercapacitors have recently attracted much attention as energy storage devices with remarkable cyclability and high power and energy densities. However, their use in high- frequency applications might be limited by a relatively slow charging process. We will first discuss the fluid structure within a slit-pore capacitor system [1] and report on the physics and optimization of charge/discharge cycles [2,3]. Step-voltage charging is slow because the coions become trapped in narrow pores of the supercapacitor electrodes. To avoid such trapping, a slow voltage-sweep charging is considered, which allows to accelerate the overall charging process substantially. We furthermore examine in detail the discharging process and will report on the effect of nonlinear charging functions. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E08.00004: Intra-chain electrostatic correlations govern charge regulation of weakly dissociating polyelectrolytes Mohsen Ghasemi, Ronald G Larson Theories for the charge regulation of weakly dissociating polymers that consider both acid-base equilibria and electrostatic interactions are poorly developed. Here, we develop a detailed model that combines an acid-base equilibrium with a random phase approximation (RPA) of electrostatic correlations for a solution containing weak polyacids. We find that charge regulation of a polyacid strongly depends on the polyacid structure: A rodlike polyacid yields the lowest electrostatic repulsions between deprotonated monomers in the chain and protons can easily dissociate from the chain, while in more compact structures, such as Gaussian coil, the polyacids do not easily give up their protons due to the higher electrostatic repulsions that would result. We find that titration of hydrophilic poly(acrylic acid) shows a response similar to our prediction for a rodlike polymer, while a Gaussian coil better models the behavior of hydrophobic poly(acrylamido-2-methyl-1-propanesulfonic acid). Our predictions highlight the significance of inclusion of chain structure in treating electrostatic correlations of polyacids, and suggest the need for self-adjustable polymer structures to obtain realistic a priori predictions. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E08.00005: Field Theory Description of Polyelectrolyte-Surfactant Coacervate Phase Behavior Jason Madinya, Charles Sing Interactions between polyelectrolytes and oppositely-charged surfactant-micelles can lead to a charge-driven liquid-liquid phase separation known as complex coacervation. These systems and their phase behavior have been studied for variety of applications including food products, personal hygiene products, and pharmaceuticals. In this work we present a field theoretic calculation(1) for modeling phase separation in charged polymer and surfactant solutions, where we treat micelle surface sites as permanent sites interacting with polymer density fields. Monte Carlo simulations of the surfactant micelle conformations determine the micelle surface site distributions, and we can subsequently evaluate the system free energy for phase diagram calculations. We treat the system as a three-component system comprised of polymer-micelle complexes, polymer-salt complexes, and solvent; the resulting ternary phase diagrams for the system can be compared to experimental results in the literature, and we can probe a number of molecular features including polymer distribution and bridging in the coacervate phase. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E08.00006: Effect of Added Salt on Disordered Poly(ethylene oxide)-Block-Poly(methyl methacrylate) Copolymer Electrolytes Neel Shah, Sajjad Dadashi-Silab, Michael Galluzzo, Saheli Chakraborty, Whitney Loo, Krzysztof Matyjaszewski, Nitash Balsara We studied the effect of salt addition on a diblock copolymer system with a negative Flory-Huggins interaction parameter, χ, indicative of attractive interactions between the two blocks. The system studied is PEO-b-PMMA with added LiTFSI salt. We studied two asymmetric PEO-PMMA block copolymers, PEO-PMMA(10-33) and PEO-PMMA(10-64), where the numbers refer to the molar masses of the blocks in kg mol-1. The SAXS profiles for PEO-PMMA(10-33) were featureless at all salt concentrations and in the neat state. In contrast, PEO-PMMA(10-64) exhibited SAXS peaks when the salt concentration was between 0.22 ≤ m ≤ 0.44, where m is molality given in mol Li/kg polymer. The thermodynamics of PEO-PMMA/LiTFSI mixtures are quantified by an effective χ parameter, χeff, obtained from fits of the SAXS data. The appearance of SAXS peaks only in the more asymmetric block copolymer is inconsistent with the SCFT of Cochran and Frederickson. However, the predictions of ionic SCFT developed by de la Cruz and coworkers predicts that in systems with negative χ, the ordered phases are only found in a narrow chimney, where the volume fraction of the ionic block is about 10%. Our experiments provide considerable support for ionic SCFT. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E08.00007: Conformation and aggregation of polyelectrolyte in poor solvents Chao Duan, Rui Wang Understanding the conformation of polyelectrolyte (PE) is not only a fundamental challenge in polymer science but also critical for understanding the folding and aggregation of proteins. Here, we develop a theory by systematically including the electrostatic interactions into the self-consistent field theory for polymers to study the single-chain conformation and multi-chain aggregation of PE in poor solvents. For the single-chain conformation, we find that a stable vesicle structure can exist at an intermediate salt concentration besides the traditional elongated pearl-necklace structure. The structure of the vesicle such as the volume of the interior hole and the thickness of the shell can be fine-tuned by controlling the external stimuli. For the multi-chain aggregation, we find a two-step nucleation to the bulk condensation transition. A metastable spherical cluster intermediate having some preferred size is formed through the first nucleation, but may elongate into rod-like cluster during the the second nucleation for releasing the electrostatic repulsion. This kinetic process may be a very general phenomenon which applies to aggregation of other charged systems such as protein or colloidal particle. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E08.00008: A computational approach to characterize gating in ion channels Carlo Guardiani, Flavio Costa, Alberto Giacomello Our contribution concerns gating, i.e. the |
Tuesday, March 16, 2021 9:36AM - 10:12AM Live |
E08.00009: Controlling the Properties of Ion Containing Polymers, Hydrogels and Membranes Invited Speaker: Monica Olvera De La Cruz Ionic materials are leading candidates for neuromorphic applications. Here we explore the physical properties, including structure, ion transport and reconfigurability of ion-containing polymers, gels and membranes in bulk and confinement for ionic devices utilization. We design, analyze, and characterize the functions of these responsive polymer composites in the presence of external fields. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E08.00010: Self Assembly of Block Copolymers in Ionic-liquid Cured Epoxy Deborah Liu, Daniel Krogstad In this work, the ability of ionic liquids to act as both a structure directing and curing agent in epoxy/block copolymer (BCP) blends is discussed. The material system consists of a bisphenol-A epoxy monomer, an ionic liquid hardener and an ABA triblock copolymer. These materials were analyzed via small angle x-ray scattering (SAXS) before and after thermal curing. Both the cured and uncured materials show a surprising variety of well-ordered and self-assembled phases which are not present in systems cured with traditional diamine curing agents. A ternary phase diagram was constructed to explore to effect of composition on observed phases. Phase changes as a function of temperature were observed via simultaneous thermal curing and in-situ SAXS. A number of order-order phase transitions were observed. The observed phases are sensitive to temperature even at temperatures well below the curing temperature of the epoxy, and thus are a function of both degree of epoxy crosslinking and free energy changes due to temperature. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E08.00011: Effect of Cluster Cohesion on Dynamics of Ionic Polymers in Solutions: MD Simulations Studies Chathurika Kosgallana, Gary Grest, Dvora Perahia Correlation of dynamics of ionizable macromolecules with the cohesion of ionic clusters is critical to understanding their properties; hence directly impacting their potential uses. Here we probe the immense effects that even a small number of ionic groups tethered to a polymer have on their dynamics, through atomistic molecular dynamics simulations. Clusters shape and size were tuned via addition of ethanol to toluene solutions of sulfonated polystyrene in the ionomer regime. The static and dynamic structure factors were measured and corelated with the characteristics of the ionic clusters. We find that the dynamics of the polymer that is constrained on the length scale of the ionic cluster in toluene is enhanced as tiny quantities of ethanol are added. While the size of the clusters is only slightly altered, the degree of association of the solvents with the ionic groups changes with addition of ethanol affecting their internal packing and ultimately their macroscopic dynamics. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E08.00012: A Coarse-grained Approach to Understanding the Behavior of Polyelectrolyte Solutions Supreet Kaur, Arun Yethiraj The behavior of polyelectrolyte solutions and coacervates is a topic of current interest. In the latter, oppositely charged polymers (and their counterions) are mixed in aqeous solution. We present a coarse-grained approach to modeling polyelectrolyte solutions, with a goal of studying large systems with adequate chemical detail, including explicit solvent. We focus on two polyions, namely polystyrene sulphonate (PSS) and polyvinylbutyltrimethyl ammonium (PVBTMA), in explicit solvent, with sodium and chloride counterions, respectively. In the development of a CG model, we find that the mapping scheme and partial charge distribution play a crucial role in the ability of the CG model to faithfully represent the atomistic model. The CG models are able to reproduce the conformational properties of single chains, as observed in atomistic simulations. Interestingly, the conformational properties of PVBTMA-Cl and PSS-Na are very similar, even though there are significant differences in the local correlations. We hope these models will aid in a molecular level understanding of complex coacervate behavior. |
Tuesday, March 16, 2021 10:48AM - 11:00AM On Demand |
E08.00013: Polyelectrolyte gels in salt solutions: a computational study Zilu Wang, Michael Shea Jacobs, Andrey Dobrynin Polyelectrolyte gels (PGs) demonstrate higher degrees of swelling and lower shear modulus than neutral polymer gels, which enables their applications as water-absorbents, cell cultivation scaffolds, artificial tissues and soft actuators. To understand the factors influencing the PG swelling, we performed coarse-grained molecular dynamics simulations of PGs in salt solutions. The equilibrium swelling ratio Q is shown to depend on the fraction of the charged monomers f and the salt concentration in the reservoir css, which together determine the salt concentration cs,g and the content of the osmotically active counterions inside PG. In particular, Q monotonically increases with the increasing fraction of charged monomers f on the polymer backbone and decreases with increasing the salt concentration. For studied PG systems, the equilibrium swelling is achieved in the non-linear network deformation regime. Therefore, to describe simulation results we use deformation dependent shear modulus G(Q). Specifically, analysis of simulation data shows that at equilibrium there is universal relationship between G(Q)/Q1/3 and cs,g/fcs,s ratio. |
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