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 S02: Molecular and Ion Transport in PolymersFocus Live
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Sponsoring Units: DPOLY DSOFT DBIO GSNP Chair: Vera bocharova, Oak Ridge National Lab |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S02.00001: Mechanisms of Diffusive Charge Transport in Redox-Active Polymer Solutions Liliana Bello, Charles E. Sing Redox-active polymers (RAPs) are a promising material for energy storage in flow batteries due their large size preventing detrimental redox material crossover and adjustable molecular chemistry and architecture for optimized performance. There has been a recent effort to understand the physics governing charge diffusion in RAPs. We use simulations and theory to show how a variety of molecular charge transport mechanisms affect diffusive motion in RAP solutions. Our coarse-grained model of RAP solutions employs Brownian dynamics for polymer motion and a kinetic Monte Carlo update step for the charge hopping dynamics. We perform these simulations for both an isolated and interacting case for single chains and multi-chain systems where we show how a various transport mechanisms interplay, including the intra-polymer transport of charge via self-exchange and polymer segmental motions, as well as hopping due to inter-polymer collisions and translational diffusion of the chains. We provide theoretical arguments to describe the diffusive motion of charge via these mechanisms, which match well with simulations. Our predictions suggest the existence of three charge transport regimes, which distinguish between inter- and intra-molecular processes and dilute and semi-dilute solutions. |
Thursday, March 18, 2021 11:42AM - 12:18PM Live |
S02.00002: Li+ Ion Migration in Polymer Electrolytes: How Coordination Effects Control Li+ Transport Mechanisms Invited Speaker: Monika Schönhoff Li salt-in-polymer systems were suggested as solid electrolytes for Li ion batteries with superior properties over common liquid electrolytes. While the classical poly(ethylene oxide) (PEO)-based electrolytes suffer from limited ionic conductivity and low lithium transference number, employing alternative polymer architectures, e.g. polyesters, is a promising approach. These differ in their Li coordination with consequences for salt dissociation and Li transference numbers. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S02.00003: Understanding the Effect of Permanent Crosslinks in Dense Polymer Networks on Probe Diffusion Grant S. Sheridan, Christopher Evans The effect of permanent crosslinks on organic probe diffusivity was investigated in networks spanning 1-50 mol% crosslink density to better understand how mesh induced confinement affects mass transport. Fluorescent dyes were placed in n-butyl acrylate networks and the translational diffusion coefficient was determined using Fluorescence Recovery After Photobleaching (FRAP) as function of the size ratio between the dye and average distance between crosslink junctions (d/l). In lightly crosslinked networks, an order of magnitude decrease in dye diffusivity is found that can be well described by a model where diffusion is slowed by segmental dynamics as the glass transition temperature increases. At larger d/l ratios, the diffusivity was observed to further decrease by an order of magnitude and was fit to a hopping model. In the densest networks, the dye diameter was larger than the distance between crosslink junction and dye diffusion, suggesting the network is hindering translation. Comparisons with scaling theories will also be discussed. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S02.00004: Dissociation of Lithium Salt in Block Copolymer Kyoungmin Kim, Leah Kuhn, Igor Alabugin, Daniel T Hallinan Transport properties of polymer electrolytes are the key information for battery design, especially with concentrated system, due to the complicated interactions between the components. Therefore, understanding the ion interaction between the elements would improve the comprehension of the complex transport behaviors of concentrated systems. In this study, the interaction between lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and polystyrene (PS) - poly(ethylene oxide) (PEO) diblock copolymer was investigated using Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) simulation. A systematic approach enabled the quantification of polymer swelling and validated the Beer-Lambert law by using the inert polymer block as a reference of the IR intensity. The spectral changes of the PEO and the anomeric effect identified via the simulation indicated PEO-Li+ coordination. This work showed how well-controlled spectroscopy experiments can be used for quantitative study of ion dissociation and interactions in concentrated and complicated electrolyte systems. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S02.00005: Role of Zwitterion Addition on Ion Conduction in Polymer Electrolytes Wenwen Mei, Joshua E Bostwick, Robert Hickey, Ralph Colby The room temperature conductivity for polymeric single-ion conductors is stifled by the limited number density of simultaneously moving ions and their mobility. The latter depends on glass transition temperature (Tg) while the former depends on dielectric constant. We find that addition of zwitterions to a model single-ion conducting polymer significantly increased the dielectric constant and slightly increased Tg. Consequently, ionic conductivity increased despite the increase of Tg. The presented work highlights the significance of dielectric constant for ion conduction in polymeric materials and suggests that if both high dielectric constant and low Tg can be simultaneously achieved, useful single-ion conducting polymers might be realized. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S02.00006: Ion Mobilities, Transference Numbers and Inverse Haven Ratios of Polymeric Ionic Liquids Zidan Zhang, Bill K Wheatle, Jakub Krajniak, Jordan R Keith, Venkatraghavan Ganesan We probe the ion mobilities, transference numbers and inverse Haven ratio of ionic liquids and polymerized ionic liquids as a function of their molecular weight using a combination of atomistic equilibrium and non-equilibrium molecular dynamics simulations. In contrast to expectations, we demonstrate that the inverse Haven ratio increases with increasing degree of polymerization (N) and then decreases at larger N. For a fixed center of mass reference frame, we demonstrate that such results arise as a consequence of the strong cation-cation correlated motions which exceed (in magnitude) the self-diffusivity of cations. Together, our findings challenge the premise underlying the pursuit of pure polymeric ionic liquids as high transference number, single-ion conducting electrolytes. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S02.00007: Probing ion diffusion in chemically amplified resists through experiments and atomistic simulations Christopher Bottoms, Tanguy Terlier, Gila E Stein, Manolis Doxastakis Quantitative reaction-diffusion models are critical to the design of high-resolution lithographic processes based on acid-catalyzed deprotection of glassy polymer resins. We present a concerted experimental and computational effort to examine diffusion of an inert catalyst analogue (a cation-anion pair) in the protected and deprotected states of a model terpolymer resin. Multi-microsecond molecular dynamics simulations provide insight into ion-ion association, polymer-ion interactions, and transport mechanisms at temperatures well-above the glass transition and reveal that ion diffusivity is slightly reduced with deprotection. Time-of-flight secondary ion mass spectrometry demonstrates that ion diffusivities are independent of extent-of-deprotection at temperatures below the glass transition. Models of reaction-diffusion based on these values capture long-time deprotection kinetics, but deviations persist at short times that are attributed to transient states generated by reaction. This study highlights the potential of atomistic modeling coupled with targeted experiments for interrogating the physical and chemical processes of patterning in next-generation lithographic materials. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S02.00008: Ion co-transport with alcohol in cation exchange membranes Jung Min Kim, Bryan Beckingham The co-transport of ionic species and alcohols in ion exchange membranes is of interest for applications such as photoelectrochemical CO2 reduction cells (PEC-CRC). In PEC-CRC, CO2 is reduced to valuable ions (e.g. formate and acetate) and alcohols (e.g. methanol and ethanol) and a lack of catalyst specificity leads to mixtures of these products. One of the major challenges in PEC-CRC is to design ion exchange membranes that minimize crossover of CO2 reduction products as upon crossover they readily oxidize back to CO2 diminishing device performance. Understanding the multicomponent transport behavior of these species in ion exchange membranes is thereby necessary to advance the design of new membranes for this and other applications. Here, we investigate the transport behavior of Nafion® 117 and PEGDA-AMPS cation exchange membranes to co-ion (formate or acetate) and alcohol (methanol and ethanol), where we observe an increase in both formate and acetate permeability in co-permeation with either methanol or ethanol. We attribute this behavior a shielding of electrostatic repulsion, in which the alcohol interferes with electrostatic repulsion between transporting co-ions and bound sulfonate anions. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S02.00009: Surface-Induced Ordering Depresses Through-Film Ionic Conductivity in Lamellar Block Copolymer Electrolytes Jonathan Coote, Thomas P Kinsey, Dayton P Street, S. Michael Kilbey, Joshua Sangoro, Gila E Stein Lamellar block copolymers based on polymeric ionic liquids (PILs) show promise as electrolytes in electrochemical devices but often display structural anisotropy that depresses the through-film ionic conductivity. This work hypothesizes that structural anisotropy is a consequence of surface-induced ordering, where preferential adsorption of one block at the electrode drives a short-range stacking of the lamellae. This point was examined with lamellar diblock copolymers of polystyrene (PS) and an acrylate-based PIL. The bulk PS−PIL structure was comprised of randomly oriented lamellar grains. However, in thin PS−PIL films (100−400 nm), the lamellae were stacked normal to the plane of the film and surface relief structures were formed when the as-prepared film thickness was incommensurate with the natural lamellar periodicity. Both of these attributes are well-known consequences of preferential wetting at surfaces. The ionic conductivity of thick PS−PIL films (50−100 μm) was approximately 20x higher in the in-plane direction than in the through-plane direction, consistent with a mixed structure comprised of randomly oriented lamellae throughout the interior of the film and highly oriented lamellae at the electrode surface. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S02.00010: Solvent Effects on the Transference Number of Dilute Polyelectrolyte Solutions Tyler Lytle, Arun Yethiraj
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Thursday, March 18, 2021 1:54PM - 2:30PM Live |
S02.00011: Understanding Gas Transport in Polymer-Grafted Nanoparticle Assemblies Invited Speaker: Sanat Kumar We measure and rationalize the unusual gas transport behavior of polymer-grafted nanoparticle (GNP) membranes, in particular focusing on their enhanced permeabilities relative to the corresponding pure polymer. For a given NP radius and grafting density in the dense brush regime we find that gas permeabilities display a maximum as a function of the graft chain molecular weight. Based on a newly proposed theory for the structure of a spherical brush, we postulate that the peak permeability for these brush constructs occurs when the densely grafted polymer brush has the highest, packing-induced extension free energy per chain. The brush thickness corresponding to this maximum extension free energy is predicted to be independent of chain chemistry and at an apparently universal value of the NP loading. Motivated by this conjecture, we measured carbon dioxide and methane permeability enhancements across a variety of NP core sizes, graft density and graft chain length, and find that they behave in a similar manner when considered as a function of NP core volume fraction, with a peak in the near vicinity of the predicted value when the chain extension free energy is maximized. Thus, the chain extension free energy appears to be the critical variable in determining the gas permeability for these hybrid materials. The emerging picture is that these curved polymer brushes, at high enough behave akin to a two layer transport medium – the region in the near vicinity of the NP surface is comprised of extended polymer chains which speed-up gas transport relative to the unperturbed melt. The chain extension free energy increases with increasing chain length, and apparently leads to an increasing gas permeability. For long enough grafts, there is an outer region of chain segments that that is akin to an unperturbed melt with slow gas transport. |
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