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 P63: Confinement, Dynamics, and Ion Interactions in Ion-Containing Polymers IIFocus Live
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Sponsoring Units: DPOLY DSOFT Chair: Moon Park, Pohang Univ of Sci & Tech; Chang Yun, Pohang Univ of Sci & Tech |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P63.00001: Impact of Frictional Interactions on Conductivity, Diffusion, and Transference Number in Ether- and Perfluoroether-Based Electrolytes Lorena Grundy, Deep Shah, Nitash Balsara Little is known about the underpinnings of ion transport in fluorinated polymer electrolytes. We use NMR and full electrochemical characterization in tetraglyme mixed with LiTFSI (H4) and in a fluorinated tetraglyme analog mixed with LiFSI (F4). Conductivity is significantly lower in F4 than in H4, and F4 exhibits negative transference numbers, while those of H4 are positive at most salt concentrations. By analyzing Stefan-Maxwell diffusion coefficients, we conclude that at low salt concentrations, the difference in transference numbers is due to differences in anion-polymer interactions. We also develop several Nernst-Einstein-like equations relating ionic conductivity to Stefan-Maxwell, instead of self, diffusion coefficients. In F4, we find that conductivity is well-described by a new regime in which the only Stefan-Maxwell diffusion coefficient influencing conductivity is the cation-anion diffusion coefficient. This implies that in F4, ionic conductivity is controlled completely by cation-anion frictional interactions |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P63.00002: Collective diffusion of nanoparticles and polyelectrolytes in confinement Svetlana Morozova, Emmanuel Hitimana, Brittany Roopnarine Transport through heterogeneous confined geometries is encountered in many processes and applications such as filtration, drug delivery, and enhanced oil recovery. To understand these complex phenomena, we have investigated dynamics of negatively-charged polystyrene particles and fluorescently labeled sodium polyacrylate in convex lens-induced confinement (CLiC). The confinement slit height was controlled from 0.085 µm to 3.6 mm by sandwiching the solutions between a glass coverslip and a convex lens using a homemade sample holder. Using differential dynamic microscopy and particle tracking, cooperative diffusive dynamics and interactions were determined. It was found that particle diffusion was more hindered as a function of increased confinement free energy, and electrostatic interactions were considerably reduced. Moreover, in high salt solutions, confinement-induced phase separation and adsorption were observed for both particles and polymers. These findings could lead to better understanding of separations and interactions in confining devices. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P63.00003: Effect of Molecular Weight on Self-Diffusion Dynamics and Viscoelasticity of Polymerized Ionic Liquids Qiujie Zhao, Christopher Evans A systematic series of polymerized ionic liquids (PILs) with various molecular weights (MW) was synthesized both with and without fluorescent labels. Size exclusion chromatography was applied to the unlabeled samples for absolute MW determination, and used to calibrate the labeled polymers. Fluorescence recovery after photobleaching (FRAP) was applied to investigate the self-diffusion of dry PILs. The self-diffusion coefficient (D) was extracted by analyzing the post-bleached fluorescence images. The diffusion coefficient monotonically increased with number of repeating units (N) but no entanglement regime was observed in the studied range. This was further confirmed by rheology where viscosity (η0) scale as ~ N 1, as unentangled polymer melts. Oscillatory measurements showed no clear entanglement or ion aggregation plateau at intermediate frequencies but the terminal region extended to lower frequencies as N increased. The lack of ion aggregation was supported by X-ray scattering data where no ion aggregation correlation peak was observed. This study provides a fundamental insight into the effect of molecular weight on dynamic properties of ionic polymer melts. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P63.00004: Mechanism of Ion Transport in Imidazolium Polymerized Ionic Liquids (PILs) Bearing a Polythiophene Backbone and in Dual Ionic Conductors of Polyfluorene Block Copolymers Doped with LiTFSI. ACHILLEAS PIPERTZIS, George Papamokos, Markus Muhlinghaus, Oskar Sachnik, Markus Mezger, Ullrich Scherf, George Floudas Understanding the mechanism of ion transport in polyelectrolytes based on Polymerized Ionic Liquids (PILs) is of great importance for increasing the RT conductivity. Herein, imidazolium PILs bearing a polythiophene backbone with four different N-alkyl side-chain lengths and seven different counteranions were synthesized and investigated with respect to the ion conduction. Cation-anion complexation strongly influences the backbone dynamics and the associated dc-conductivity. Ionic conductivity measurements as a function of pressure revealed that ion motion is facilitated by local anion jumps with a length scale on the order of the charge alternation distance. A simple “stick and jump” model can account for the increased backbone mobility and the concomitant enhanced ion conductivity for anions with intermediate size ([TFSI]-). |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P63.00005: Cation Transport in Ionic Layers of Sulfonated Crystalline Telechelic Polyethylenes Benjamin Paren, Manuel Haeussler, Stefan Mecking, Karen Winey We present a set of sulfonated telechelic polyethylene ionomers that demonstrate ion transport of metal cations within layered ionic aggregates in a crystalline polymer matrix. These precise ionomers consist of 48 backbone carbons with sulfonated end groups that are fully neutralized by a counterion, C48(SO3X)2 (X=Li+ or Na+). The morphology is characterized using X-ray scattering and ion conductivity is characterized using electrical impedance spectroscopy. These telechelic polyethylenes exhibit well defined ionic layers and a variety of crystalline backbone morphologies below Tm. The polyethylene backbone packs in a hexagonal crystal at high temperatures in both the Li+ and Na+-containing systems, with an Arrhenius activation energy (Ea) for ion transport of 120 and 53 kJ/mol, respectively, indicating decoupled ion transport through the layers. The Ea in the hexagonal regime is significantly lower than Ea in the room temperature backbone morphologies of these polymers, orthorhombic in C48(SO3Na)2, and disordered crystals in C48(SO3Li)2. The low Ea of 53 kJ/mol in the hexagonal regime of C48(SO3Na)2 is a promising sign for the ability of ionic layers to facilitate ion transport in crystalline polymers, for potential application as solid polymer electrolytes. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P63.00006: Understanding the role of dynamic bonds on conductivity in dense polymer networks Christopher Evans, Brian Jing, Chengtian Shen, Qiujie Zhao We have investigated a series of ethylene oxide networks containing a range of permanent and dynamic crosslinks to understand the role of bond exchange on conductivity. All systems are studied with added LiTFSI salt, and in the case of permanent networks a suppression in conduction is observed as the mesh size decreases. Next, electrolytes with dynamic boronic ester bonds (which exchange in a topology conserving manner) were synthesized which show a massive drop in modulus and stress relaxation times with salt addition, attributed to boron-anion interactions. Analogous networks were also prepared with a slower exchanging dynamic bond (vinylogous urethane) which show a similar drop in stress relaxation times, but essentially unchanged modulus with salt addition. In all cases, an optimal conductivity is observed with added salt before aggregation occurs. This work shows the distinct responses which can be achieved in dynamic network electrolytes, and how modulus can be decoupled from viscosity in ionic materials. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P63.00007: Utilizing ionic liquid networks to explore fundamental principles in soft electro-adhesion Elayne Thomas, Hyeong Kim, Matthew Kent McBride, Ryan Hayward, Alfred Crosby Ion-conducting polymers show potential for designing new classes of soft robotics and interfaces. Understanding soft material interfaces is particularly important in electro-adhesion, a mechanism that enables controllable and switchable adhesion via an electric field. Although previous contributions have provided insight into how applied voltage and interfacial attraction forces affect electro-adhesive performance, a general framework that unites the far-field materials properties, applied voltage, and geometric constraints has not been developed. We utilize two cross-linked ionic liquid networks, coined “ionoelastomers”, that exhibit modular and switchable electro-adhesion through an applied bias via the formation of an interfacial ionic double layer (IDL). We present a predictive model for electro-adhesion that captures the force capacity as a function of voltage, elastic modulus, interfacial dimensions, and sample thickness. Our results carry significant implications to guide electro-adhesive materials and device design to use ion-conducting networks for low power consumption and energy dissipation. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P63.00008: Ionic Conductivity Enhancement Through Directed Crystallization Polymer Electrolytes Changhao Liu, Xiaomin Tang, Yangyang Wang, Jong Keum, Xi Chen Polymer electrolyte (PE) is promising for solid-state lithium metal batteries due to its flexibility, chemical stability, and processibility1. However, common poly(ethylene oxide) (PEO) based PE suffers from low room temperature conductivity due to its crystallinity. The randomly oriented PEO crystals in unaligned samples increase the tortuosity of the conduction pathway and hinder ion transport efficiency2. Our goal here is to improve the conductivity of PE through directed crystallization. PEO/lithium triflate salt is used as a model system. To achieve aligned crystallization, the polymer electrolyte film is hot drawn at 90 °C followed by crystallization at a lower temperature with the strain maintained. Wide-angle X-ray scattering experiments indicate that the (120) and (032) planes of PEO crystals are oriented and the degree of orientation increases with the stretching ratio. As a result, the through-plane conductivity increases by nearly a factor of 5. The effect of crystallization temperatures and different lithium salt on conductivity will also be discussed. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P63.00009: Ion Dynamics in Ionic Liquids Polymerized in situ within Silica Nanopores Thomas P Kinsey, Joshua Sangoro Polymerized ionic liquids are a promising class of versatile solid-state electrolytes for applications ranging from electrochemical energy storage to flexible smart materials that remain limited by their relatively low ionic conductivities compared to conventional electrolytes. In this talk, we will show that the in-situ polymerization of the vinyl cationic monomer, 1-ethyl-3-vinylimidazolium with the bis(trifluoromethanesulfonyl)imide counter anion, under nanoconfinement within 7.5 (± 1.0) nm diameter nanopores results in a nearly 1000-fold enhancement in the ionic conductivity compared to the material polymerized in bulk. Using insights from broadband dielectric and Raman spectroscopic techniques, we attribute these results to the role of confinement on molecular conformations, ion coordination, and, subsequently, the ionic conductivity in the polymerized ionic liquid. These results contribute to the understanding of the dynamics of nanoconfined molecules and show that in-situ polymerization under nanoscale geometric confinement is a promising path towards enhancing ion conductivity in polymer electrolytes. |
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P63.00010: Effect of Pore Topology on Ionic Conductivity in Hybrid Electrolytes Vazrik Keshishian, Cameran Beg, John Kieffer To simultaneously achieve high ionic conductivity and mechanical stiffness, we pursue a hybrid organic-inorganic nanocomposite materials design for developing solid-state electrolytes (SSE). We first create a continuous silica network via sol-gel synthesis to provide a mechanically rigid backbone. During subsequent fluid exchange, the polymer is grafted onto the backbone through reactive groups and anchored into structure to establish the ion conducting phase. This approach allows to decouple the mechanical from the ionic transport properties and augment both simultaneously. The network of the gel-cast material is further conditioned by influencing structural evolution during drying. Changing sample aspect ratio introduces various degrees of anisotropy and spatial gradients in the network topology, as revealed by nano-mechanical characterization using Brillouin light scattering, as well as ion mobility. The strong correlation between the adiabatic elastic modulus and the activation energy of ion hopping has led to developing an improved transition state theory model for this process, which we use to develop materials design strategies for harnessing this structural conditioning and create better performing SSE. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P63.00011: Gyroid Morphologies in Single-ion Conducting Multiblock Copolymers: A Phase Diagram and Efficient Ion Transport Jinseok Park, Anne Staiger, Stefan Mecking, Karen Winey We investigated the nanoscale morphologies and ionic conductivities of polyethylene-based multiblock copolymers as single-ion conducting polymers. These polymers contain short polar blocks with a single sodium sulfonate group separated by polyethylene blocks of fixed length (PESxNa, x = 10, 12, 18, 23, 48). At room temperature, these polymers exhibit layered ionic aggregates with semicrystalline polyethylene backbones. For PES12Na, PES18Na, and PES23Na, the layered morphologies transition into gyroid morphologies upon melting of the polyethylene blocks, and further transition into hexagonal morphologies at higher temperatures. In contrast, PES10Na and PES48Na exhibit layered to hexagonal transitions at the melting temperature, without an intermediate gyroid morphology. The phase diagram of these PESxNa polymers is well-matched with the conventional diblock copolymers and identifies the presence of gyroid morphologies at the volume fraction of polar blocks 0.27 - 0.41. Ionic conductivities reveal the faster ion transport through bicontinuous gyroid than hexagonal morphologies, and its relationship to the interaggregate spacings. This new phase diagram develops design strategies for single-ion conducting polymers with a bicontinuous ionic aggregate and efficient ion transport. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P63.00012: Role of chain architecture and composition on dynamics and ionic solvation in polyether-based electrolytes Peter Bennington, CHUTING DENG, Daniel Sharon, Michael Webb, Juan De Pablo, Paul F Nealey, Shrayesh Patel Ion conducting polymers based on ethylene oxide (EO) repeat units are widely studied for use as electrolytes in lithium ion batteries. A molecular level understanding of the relationship between polymer chain architecture and ion conduction, however, remains unclear. We have compared the conductivity, ionic interactions, and polymer dynamics of a series of graft polyethers using a combination of impedance spectroscopy, vibrational spectroscopy, and atomistic scale molecular dynamics (MD). We find that side-chain length dictates large differences in the measured conductivity, despite modest differences in the calorimetric glass transition temperature (Tg) of the various materials. A temperature dependence in the conductivity of graft polyethers compared to linear PEO is explained by heterogeneous EO unit dynamics in the graft systems, arising from a comparatively immobile backbone. Importantly, these differences in polymer segmental mobility were not captured by experimentally observed Tg and were only apparent through the use of fine-grained MD simulations. |
Wednesday, March 17, 2021 5:24PM - 6:00PM Live |
P63.00013: Hydroxide conducting block copolymers Invited Speaker: Yossef Elabd Hydroxide ion conducting block copolymers have the potential to possess the multiple orthogonal properties required for anion exchange membranes to enable long-lasting alkaline fuel cell performance, and therefore can accelerate the advancement of the alkaline fuel cell, a low-cost alternative to the well-adopted commercial proton exchange membrane fuel cell. In this work, an overview of hydroxide ion transport (a property that is proportional to fuel cell performance) in block copolymers will be presented and the subsequent impact of block copolymer morphology on ion transport (conductivity), where the careful design of block copolymer chemistry and chain architecture can accelerate hydroxide ion transport and subsequently alkaline fuel cell performance. |
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