Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D05: Charged and Ion-Containing Polymers II |
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Sponsoring Units: DPOLY Chair: Thomas Gartner, Georgia Institute of Technology Room: Room 128 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D05.00001: Ion Correlations and Partial Ionicities in Lamellar Phases of Block Copolymeric Ionic Liquids Zidan Zhang, Jacob Sass, Jakub Krajniak, Venkatraghavan Ganesan Recently, significant interest has arisen on the impact of dynamical ion correlations on the conductivity and transport properties of polymeric electrolyte materials. It has been hypothesized that confining ion motion to narrow channels may reduce such ion correlations and enhance the resulting ionic conductivity. Motivated by such considerations, in this study we used a multiscale simulation framework to study the dynamical ion correlations in microphase separated lamella phase of block copolymeric ionic liquids and compare with the corresponding results for homopolymeric systems. We probed the influence of ion correlations through the partial ionicity, D, which quantifies the ratio of true conductivity to the ideal, Nernst-Einstein conductivity for the anion related contributions. Consistent with our original hypothesis, our results demonstrate that the partial ionicity relating to the mobile anions is much larger in the lamella phases of block copolymers compared to that in homopolymers. Analysis of the distinct conductivity contributions demonstrates that such results arise as a result of an intricate compensation among the non-ideal dynamical correlations relating to anions in lamella phases. Together, our results suggest that self-assembled phases of block copolymers may provide an avenue to tune the dynamical ion correlations in polymer electrolyte systems. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D05.00002: Dielectric Constant of a Polymerized Ionic Liquid with Rigid Side Chains Cameron Shock, Mark J Stevens, Amalie L Frischknecht, Issei Nakamura Recent experiments suggest that polymerizing ionic liquids can result in unconventional increases in the dielectric constant, yet the mechanism for this remains unclear. We probe these results with molecular dynamics simulations in LAMMPS using the Stockmayer fluid model, in which the polymers are treated as chains of charged (or neutral) dipolar spheres. We have implemented a novel method to restrict the dipole motion by treating the dipolar, ionic sidechains as rigid bodies attached to a semi-flexible backbone. We determine the effects of this constraint on the dielectric constant, dipole order and dipole correlations, and how these quantities differ from the case of freely-rotating dipoles and from experiment. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D05.00003: Poly(siloxane) Derived Ionosilicone Elastomers Reveal Role of Backbone Dynamics in Ionic Double Layer Formation Owen Lee, Matthew K McBride, Ryan C Hayward Poly(siloxane) ionic liquids (PSILs) are a group of single-ion conducting polymers in which a weakly coordinating ion is covalently bonded to a siloxane backbone. The highly flexible siloxane backbone affords these polymers low glass transition temperatures and high room temperature, solvent-free ion conduction, making them a promising option for ion-mediated devices. Here, highly conductive, crosslinked cationic and anionic PSILs consisting of bulky ionic liquid moieties covalently linked to a poly(mercaptopropylmethylsiloxane) backbone were prepared. The backbone of these crosslinked PSILs can be tuned by copolymerization with acrylate monomers to create PSIL-acrylate hybrid networks with intermediate properties. When two oppositely charged PSIL-acrylate hybrid networks are brought into contact, an ionic double layer (IDL) consisting of fixed cations and anions is formed and the heterojunction exhibits diode-like, nonlinear conductance. The more mobile networks (i.e., more PSIL content) were able to rectify current at higher frequencies in response to a constant DC overpotential. Interestingly, the capacitive nature of the IDL under reverse biases was diminished with increasing temperature, elucidating the importance of interfacial polymer dynamics on heterojunction performance. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D05.00004: Influence of Poly(methyl methacrylate) Inclusion on Ion Dynamics and Conduction Mechanism of Imidazolium Ionic Liquids Ruhao Li, Pinar Akcora Our previous studies on poly(methyl methacrylate) (PMMA)-grafted nanoparticles in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (HMIM-TFSI) showed that polymer-ionic liquid interactions influence the solvation and dynamics of ionic liquid. In this study, we analyzed the dielectric relaxation, activation energy and frequency-dependence of ionic conductivity of PMMA containing imidazolium ionic liquids. We found that interactions between PMMA and TFSI- anions disturb the cage structure and accelerate the HMIM+ cation motion, thus increase the apparent ionicity of HMIM-TFSI. Imidazolium ionic liquids with the addition of PMMA-grafted and poly(1-vinylimidazolium bis(trifluoromethylsulfonyl)imide) (PVIm-TFSI)-grafted nanoparticles will be also discussed to reveal the role of percolating structures on the ionicity. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D05.00005: Ion Transport in Polymer Electrolytes: Effect of Glass Transition Temperature Alexandros Tsamopoulos, Zhen-Gang Wang Polymer Electrolytes (PEs) are promising alternative materials to conventional organic electrolyte systems since they are nonflammable and suppress lithium dendrite growth. However, PEs possess much lower ionic conductivity undermining their ability to be used in lithium-ion batteries. It has been suggested that polymer segmental relaxation is one of the main mechanisms of Li+ transport. Given a polymer chemistry, this mechanism is correlated to the glass transition temperature (Tg). However, a systematic understanding of the dependence of Tg on system properties is still lacking. To this end, we conduct coarse-grained molecular dynamics simulations of salt-doped polymers. In our work, we focus on the combined effects of temperature and salt concentration on ionic conductivity and how glass transition affects ion transport, within the same polymer. Our results hint towards a temperature-salt concentration superposition of the ionic conductivity. We will present possible implications of this finding and its relation to the glass transition temperature. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D05.00006: Ion transport in single anion conducting polymer networks Chen Chen, Christopher M Evans, Paul V Braun Network polymer electrolytes offer promising to provide both mechanical strength and ionic conductivity, but few fundamental studies have been performed on such structures. Here, single anion conducting networks were synthesized via radical copolymerization of an anionic methacrylate, PEG methacrylatem and a dimethacrylate crosslinker as study system. The effects of cation chemistry, crosslink density and comonomer side chain length will be discussed. Dielectric spectroscopy was performed to study segmental relaxation, ionic conductivity, and their relation. Calorimetric Tgs remained nearly constant over the crosslink density range of 1% to 40%, while dielectric Tg, defined at the dielectric relaxation time equal to 10-4 s, increased with crosslink density up to 20 K over this range. Angell plot (conductivity vs. Tg/T) shows that calorimetric Tgs do not explain the effect of crosslink density while conductivity collapsed on a dynamic Tg normalized plot. Walden plots (relaxation time vs. conductivity) suggested conductivity was strongly coupled with segmental movement. Other analysis based on dielectric spectroscopy were also performed. Static dielectric constant and the number density of simultaneously conducting ions were also showed to be affected by crosslink density. Our work may provide a guide in design polymer electrolytes for ion-transport applications, including polymer electrolytes for electrochemical energy storage. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D05.00007: Swelling and Nonlinear Deformation of Polyelectrolyte Gels in Salt Solutions Zilu Wang, Michael S Jacobs, Yuan Tian, Andrey V Dobrynin Polyelectrolyte gels (PG) made by crosslinking ion-containing polymers demonstrate unique swelling capabilities with their volumes increasing up to 100 times in salt-free solutions. The swelling of polyelectrolyte gels in salt free solution is promoted by the osmotic pressure of free counterions localized within the gel volume due to the Donnan equilibrium. The presence of salt ions results in an exponential screening of the electrostatic interactions and a significant reduction of the osmotic effect of counterions, suppressing PG swelling ability. To quantify this effect as well as strand nonlinear deformation in PGs, we performed coarse-grained molecular dynamics simulations of the swelling and biaxial deformation of a polyelectrolyte gel film immersed in a salt solution. The simulations were performed at a constant pressure in the normal to deformation plane direction which allowed to maintain the constant salt concentration outside the gel film. The gel mechanical properties were studied as a function of the fraction of ionizable groups on the polymer backbone, degree of polymerization between crosslinks, and salt concentrations in both linear and nonlinear deformation regimes. Our simulations have confirmed that the gel swelling ratio increases with decreasing solutions salt concentration and increasing fraction of ionizable groups on the polymer backbone. Furthermore, the gel deformation in contact with a salt reservoir results in partitioning coefficient of small ions to converge to unity. The results of computer simulations are analyzed in the framework of the Flory-Rehner theory of gel swelling modified to account for nonlinear network deformations. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D05.00008: Entropic Penalty Governs Solvation Site Formation and Ion Transport Mechanisms in Mixed Polarity Copolymer Electrolytes Chuting Deng, Peter Bennington, Regina J Sánchez, Shrayesh Patel, Paul F Nealey, Juan J De Pablo Recent solid polymer electrolyte (SPE) designs for Li+ conduction considers a synergistic polarity and mobility contrast to achieve improved conductivity. To assess such idea, we employ molecular dynamic (MD) simulations to compare Li+ solvation and transport behaviors in poly (oligoethylene methacrylate) (POEM) versus in its copolymers with poly(glycerol carbonate methacrylate) (PGCMA). Unexpectedly, Li+ is not solvated by the highly polar PGCMA, but by ether oxygens (EO) instead due to a lower entropic penalty. The presence of PGCMA promotes single-chain solvation and thereby suppresses inter-chain Li+ hopping. The conductivity difference between PGCMA-r-POEM and the less-mixed PGCMA-b-POEM is explained in terms of hybrid solvation site formation at varied degrees of local composition fluctuation. This work elaborates on how thermodynamic driving forces govern solvation site formation and Li+ transport in mixed SPEs containing microscopic interfaces. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D05.00009: Understanding the High Cation Transference in Poly(pentyl malonate) Electrolyte Chao Fang, Rui Wang The development of new battery electrolyte rests on the molecular level understanding of ion transport. The recently synthesised poly(pentyl malonate) (PPM) electrolyte exhibits promising cation transference, limiting current and electrochemical stability over the benchmark poly(ethylene) oxide (PEO) electrolyte. We elucidate the molecular origin of the faster Li+ dynamics in PPM by using molecular dynamics simulations. The current fraction of Li+ and ionic conductivity obtained from the Onsager approach quantitatively agree with experimental measurements at all salt concentrations. While the ionic conductivity is comparable with the state of the art PEO-based electrolyte, the current fraction is more than 3 fold of that in PEO. In contrast to the tight chelation of Li+ by single PEO chain, the simulation reveals the coordination of Li+ involves more than one PPM chains. The distinct multi-chain coordination in PPM is also reflected by the different molecular origin of the scattering peak that arises with increasing salt concentration. Dynamically, this multi-chain coordination in PPM promotes the frequent jumping of Li+, which overcomes the moderately infrequent interchain hopping in PEO electrolytes. A larger cation-cation correlation than anion-anion correlation can be realized in PPM electrolyte, hence enabling the high current fraction. |
Monday, March 6, 2023 4:48PM - 5:00PM Author not Attending |
D05.00010: Characterization of SEO/LiTFSI Electrolytes by Electrochemistry and X-ray Scattering at High Salt Concentrations Lily A Gido Polymer electrolytes have been studied extensively as a non-flammable alternative to commonly used liquid electrolyte in rechargeable lithium metal anode batteries. Polystyrene-block-poly(ethylene oxide) (SEO)/Lithinum bis(trifluoromethanesulfonyl)imide (LiTFSI) is a well studied and ideal choice making use of the polystyrene block to provide structural rigidity while the poly(ethylene oxide) block functions well as a charge carrier. Presented is a full electrochemical characterization of this system in the concentration range of r = 0.01 to r = 0.50. Notably, the system experiences a steep drop in the maximum applicable current before potential diverges, or limiting current, between the concentrations of r = 0.20 and r = 0.25. The limiting current then plateaus between concentrations of r = 0.25 and r = 0.50. Here we aim to explain this behavior using small angle x-ray scattering (SAXS) to probe morphology changes and wide angle x-ray scattering (WAXS) to study crystallization behavior surrounding this drop in limiting current. |
Monday, March 6, 2023 5:00PM - 5:12PM Author not Attending |
D05.00011: Changes in the order-to-disorder transition in salt-doped, polar block copolymer Colin Gillespie, Robert A Riggleman Multiblock polymers, absent other intermolecular forces, typically aggregate into ordered structures with well-known behavior. This separation is characterized by the Flory-Huggins χ parameter, which generally encapsulates all enthalpic effects into a single parameter. While this model preforms well for materials dominated by relatively simple van der Waals forces, it loses fidelity when more complex intermolecular forces come into play. Introducing ions into a multiblock polymer with high dielectric mismatch is predicted to produce a regime dominated by solvation effects. In this work, we use coarse-grained polymer models to study the order-to-disorder transition (ODT) in a series of block copolymers with a dielectric mismatch between the blocks in the presence of charges. Two distinct charge architecture are compared, one with the anion free and the other with the anion integrated in the backbone. We find that this simple change in the anion placement has a significant effect on the ODT, and the changes depend on the relative salt concentration and the dielectric mismatch between the two blocks. We will discuss the resulting trends in the ODT in the context of recent experiments and theoretical predictions. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D05.00012: Complex Spherical Phases in a Zwitterion-tethered Diblock Copolymer Melt Bradley J Grim, Frederick L Beyer, Matthew D Green A recent surge of work has taken place over recent years concerning complex spherical morphologies in block polymers, including Frank-Kasper phases. The stability of such phases has been shown to rely heavily on conformational asymmetry which captures differences in statistical segment lengths between the constituent blocks. While differing polymer chemistries offer a small range of statistical segment lengths, conformational asymmetry can be enhanced via architectural and polymer dispersity modifications. Using these ideas, the number of neutral (non-ionic) block polymers exhibiting complex spherical phases is growing quickly while continuing to remain exceptionally rare for ion-containing block polymers. This may be due in part to the strong impact electrostatic interactions have on the phase behavior of block polymers. Since continuous morphologies such as Frank-Kasper phases are highly desirable in the design of ion-containing block polymers, it is important that we understand the relationships between conformational asymmetry, electrostatics, and the overall self-assembly of such systems. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D05.00013: Conformational Study of Polyelectrolytes under solvophilic and solvophobic conditions Anish Gulati, Carlos G Lopez The scaling theory for polyelectrolyte solutions1 predicts the conformation of polyelectrolytes under different conditions. A partially collapsed necklace conformation of polyelectrolytes under solvophobic conditions has been experimentally reported2, in agreement with earlier theoretical and simulation work. Though similar conformations have been predicted under some solvophilic environments at low dielectric constants (ε), experimental studies on the influence of solvent permittivity on polyelectrolyte conformation have not been performed. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D05.00014: Understanding Molecular Packing within Ionomer Domains of Materials Characterized by Small Angle Scattering Jason Madinya, Arthi Jayaraman Ionomers are a class of charged polymers that typically contain less than 15 mol% iononized or acidic pendant groups bonded to a low dielectric polymer backbone. [1] Materials containing ionomers are used in many applications including adhesives, coatings, and membranes. Perfluorosulfonic acid (PFSA) (e.g., Nafion) is one such example used in proton-exchange membranes due to its high proton conductivity and mechanical stability in the hydrated state. There is considerable interest in understanding the molecular packing and morphology in these PFSA materials and linking structure to the ion-conducting and mechanical properties. Structural characterization of PFSA materials typically involve small angle and wide-angle scattering with small angle X-ray scattering profiles of hydrated PFSA exhibiting a characteristic “ionomer peak”. Analytical model fits or computational approaches like CREASE [2] are needed to link the ionomer peak in SAXS profiles to hydrophilic ionomer domain sizes and shapes. To elucidate the molecular packing within the domains that give rise to the ionomer peak, we are conducting dissipative particle dynamics (DPD) simulations; this talk will present these simulation results. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D05.00015: Molecular Dynamics Simulation of Nanocomposite-Polyelectrolyte Hydrogels Shoumik Saha, Dilip Gersappe Nanocomposite-polyelectrolyte hydrogels are gels formed from a mixture of charged polymer chains and nanofillers. They have enhanced properties, can absorb large amounts of water, and potentially serve as a sustainable alternative to concrete for soil strengthening purposes. Despite the large number of studies on polyelectrolytes and their interactions with charged particles, little is known about the mechanism of network formation in a charged hydrogel system. Thus, we use molecular dynamics (MD) simulations to investigate the effect of charge distribution on the gelation of our system and related properties including viscosity; network formation; cluster geometry; and polymer adsorption onto filler particles. We used a coarse-grained approach where nanofillers were modeled as rigid disk-like platelets while polyelectrolytes were modeled as linear charged chains. System also included uncharged solvent particles and free-floating univalent counterions to ensure electroneutrality. Crosslinks were simulated by using pure Coulombic forces, as well as in a combination with physical forces. Our results show that the assembly of nanofillers is an important determinant of the physical properties of the gel mediated by the types of interactions between chains and nanofillers. |
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