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 S03: Dynamics of Polymers and Electrolytes in Bulk and in ConfinementFocus Live
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Sponsoring Units: DPOLY GERA Chair: Naresh Osti, Oak Ridge National Lab; Laura-Rox Stingaciu, Oak Ridge National Lab |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S03.00001: Neutron Scattering Derives Insights into Dynamics of Functional Materials Invited Speaker: BORIS DYATKIN This presentation will discuss the neutron-scattering-resolved dynamics of three distinct systems and correlate measured diffusion and mobility parameters with complementary materials characterization and computational modeling results. In unison, these findings provide comprehensive descriptions of these systems, which, to date, have not been fundamentally understood. First, this presentation will discuss the effect of oxygen- and nitrogen-containing functional groups on nanosized pores of carbide-derived carbon supercapacitors. Neutron scattering-derived results demonstrate the degree to which interactions at electrode-electrolyte interfaces influence pore filling densities and mobilities of ionic liquid electrolyte ions. The presentation will further expand the scope of the studied systems to demonstrate how degrees of confinement, including the pore dimensions, size of electrolytes, and planar non-porous interfaces shift the relative significance of these surface moieties on resulting energy and power densities. This presentation will discuss the effect of hydrated water on the ligand-ligand and ligand-solvent dynamics, as well as the propensity to delaminate, of a cobalt metal-organic framework. Finally, this presentation will discuss how temperature- and time-resolved curing dynamics of three distinct phthalonitrile resin monomers change during their molten state, gelation period, and cross-linked regimes. These approaches provide important insights into materials that demonstrate unique promise in a diverse engineering applications, and the presented model systems advance future studies that optimally integrate neutron scattering, computational modeling, materials characterization, and prototype testing. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S03.00002: Large Diffusion Coefficient of BMIM BF4 in Porous Carbon Fibers John Elliott, Naresh Osti, Madhusudan Tyagi, Eugene Mamontov, Lifeng Liu, Joel Serrano, Ke Cao, Guoliang Liu Confinement of ionic liquids in hydrophilic porous solid media has previously been shown to disrupt the lattice structures of the ionic liquids. An immobile ion layer adheres to the material surface, while the inner layer exhibits increased mobility. In this work, porous carbon fibers (PCF) synthesized from a polyacrylonitrile-block-polymethyl methacrylate (PAN-b-PMMA) block copolymer were used to study the dynamics of confined 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4). PCF contain mesoporous networks with unimodal pore size distributions. Elastic neutron scattering scans confirmed confinement in 13.6 nm diameter pores due to a lack of a freezing point between 20 K and 300 K. Quasi-elastic neutron scattering (QENS) was used to determine the diffusion coefficients of the bulk BMIM BF4 and the confined BMIM BF4. A seven-fold increase in diffusion coefficient was obtained for the confined BMIM BF4 compared to the bulk. The tunability of the PCF offers opportunities for further work exploring the limits of confinement in the unique mesoporous networks of PCF. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S03.00003: Effect of mild nanoscopic confinement on the dynamics of ionic liquids Olaf Holderer, Daria Noferini, Henrich Frielinghaus Ionic liquids, i.e. molten salts without an additional solvent, are discussed as innovative solvents and electrolytes in chemical processing and electrochemistry. A thorough microscopic understanding of the structure and ionic transport processes is essential for tailored applications. In this contribution, we study the influence of ‘‘mild’’ nanoscopic confinement on the structure and diffusion properties of an ionic liquid, 1-ethyl-3- methylimidazolium acetate, using neutron and x-ray scattering techniques. The structure is analyzed by X-ray diffraction, while neutron backscattering spectroscopy is used for the study of the diffusion processes in these systems. Interpreting the diffusion processes in terms of a jump-diffusion model allowed us to deduce the confinement effects on the jump length and residence time, both increased at elevated temperatures in confinement. The applied ‘‘mild’’ confinement, which leaves room for 10–25 times the domain spacing, allows us to observe in great detail how the onset of domain distortion decelerates the dynamics. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S03.00004: Impact of Pressure on the Dynamics of a Room Temperature Ionic Liquid Naresh Osti, Bianca Haberl, Niina H Jalarvo, Reinhard Boehler, Jamie Molaison, Richard Goyette Jr., Eugene Mamontov Room temperature Ionic liquids are considered promising electrolytes for electrical double layer capacitors because of their high thermal and chemical stability together with low volatility and large operational voltage window. Nano-scale structural heterogeneity of an ionic liquid arises from several interactions (chemical bonding and Columbic) among the constituent ions and impacts the microscopic dynamics. Use of extreme environmental conditions such as high pressure alters those interactions, which are linked to the functionality of ionic liquids. Here, we report the high pressure (up to 1.0 GPa) induced structure and dynamics change in a RTIL, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI), probed using x-ray and quasi-elastic neutron scattering techniques. The transition of the ionic liquid into the solid state at higher pressure and its return to the liquid state under decompression, associated with ions dimers formation, will be discussed. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S03.00005: Spatiotemporal Mapping of Mesoscopic Polymer Dynamics Zhiqiang Shen, Jihong Ma, Jan-Michael Carrillo, Wei-Ren Chen, Bobby G Sumpter, Yangyang Wang The study of liquid dynamics at mesoscopic scales is still strewn with difficulty due to limitations in theory and experiment. Historically, significant attention has been given to the analysis of space-time correlation functions and their frequency-Fourier-transforms at a few discrete wavenumbers. The massive computing power afforded by modern HPC clusters and the advent of wide-angle neutron spin-echo spectrometer, however, have unlocked a more intuitive and powerful approach to this problem. Using molecular dynamics simulations, here we demonstrate the benefits of spatiotemporally mapping intermediate scattering functions on a dense grid of correlation times and wavenumbers. We show that this approach is particularly useful for elucidating the mesoscopic dynamics in polymeric liquids. Compared to the traditional method, direct visualization of density space-time correlation functions on two-dimensional colormaps permits appraisals of complicated dynamical behavior at mesoscales in an "impressionistic" manner. The new perspective offered by the spatiotemporal mapping method should prove useful for the study of liquid dynamics in general. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S03.00006: d-Spacing Effect on the Electrochemical Performance of MXene in Room Temperature Ionic Liquid Electrolyte KUN LIANG, Ray Matsumoto, Wei Zhao, Naresh Osti, Madhusudan Tyagi, Eugene Mamontov, Ivan Popov, Alexei Sokolov, Bishnu Thapaliya, Simon Fleischmann, Kaitlyn Prenger, Veronica Augustyn, Sheng Dai, Peter Thomas Cummings, Michael Naguib MXenes exhibit excellent capacitance at high rates in aqueous electrolytes specially in H2SO4 aqueous electrolyte, but in a narrow potential window, which limits the energy density. Moreover, oxidation of Ti3C2 under high anodic potentials in aqueous electrolytes further limits its use to cathodes of asymmetric devices. Organic electrolyte and room temperature ionic liquids (RTIL) provide larger potential window, leading higher energy density. In this work, different intercalants were introduced in-between Ti3C2Tz, producing different interlayer spacing (d-spacing). RTIL were employed as electrolytes to investigate the d-spacing effects on electrochemical performance for three-electrode system. As a result, intercalated Ti3C2Tz, provides much broader operating window of 3.2 V, showing much higher specific capacitances of 257 F/g, energy and power densities of 256 Wh/kg and 46000 W/kg, respectively, and cycling stability than pristine Ti3C2Tz. In addition, the electrochemical performance, ions dynamics were investigated by ex situ X-ray diffraction (XRD), broadband dielectric spectroscopy (BDS) and quasi elastic neutron scattering (QENS) spectra. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S03.00007: Mechanism of Ion Transport in Solid Polymer Composite Electrolytes Yage Huang, Yunlong Guo Slow ion transport at ambient temperature impedes the practical use of solid polymer composite electrolytes (PCE). The underlying mechanism for the ionic conductivity are elucidated diversely, such as poor percolation network of fillers and sluggish segmental motions of the polymer. In this talk, we demonstrate that the polymer-ceramic particle interfacial polarization and segmental motion are directly coupled, both quantitively determine ion transport in PCE. Moreover, two different mechanisms enhance ionic conductivity in PCE, by either increasing concentration of ions participated transport or by increasing ion mobility. Accordingly, an ionic conductivity of 1.3 × 10-3 S/cm in PCE can be achieved at 30 °C. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S03.00008: Experimental determination of entropic barrier in topologically frustrated polyelectrolyte dynamics Kuo Chen, Murugappan Muthukumar The dynamics of a guest polyelectrolyte chain inside a polymer matrix has been extensively studied in the past decades and several mechanisms, such as the Ogston model, entropic barrier model, and reptation model, have been proposed to interpret the experimental data. Recent experiments reported in the literature point to a new dynamical regime of non-diffusive localization of the guest molecule due to simultaneously operative multiple entropic barriers. With fluorescence microscopy and single-molecule electrophoresis, we have directly observed this phenomenon and evaluated the magnitude of the effective entropic barrier. In our experiments, YOYO-1 labeled λ-DNA was chosen as the charged guest polymer and poly (acrylamide-co-sodium acrylate) polyelectrolyte hydrogel was used as the host matrix. Both the electric field strength dependence of electrophoresis velocity and the non-uniformity of movement indicated a critical electric field strength, Ecritical, needed to activate the motion of localized DNA chain. The entropic barrier deduced from Ecritical is of the order of tens of kBT (depending on the mesh size of the host matrix) and close to theoretically calculated values based on the topological frustrated polymer dynamics. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S03.00009: Understanding near surface polymer dynamics: neutron and virtual experiments Tetyana Kyrey, Marina Ganeva, Judith Witte, Stefan Wellert, Olaf Holderer Neutron spin-echo spectroscopy is a unique experimental method for an investigation of the polymer dynamics. The combination of neutron spin-echo spectroscopy with grazing incidence geometry (GINSES) opens the possibility to probe dynamics of the soft matter materials in the vicinity to the solid substrate in the time range up to 100 ns. However, the usage of the GINSES technique has some peculiarities and, due to the novelty of the method and complexity of the scattering geometry, difficulties in further data analysis appear. In the current work we discuss how virtual experiments within the distorted wave Born approximation (DWBA) with the BornAgain software can improve the GINSES data treatment and help to understand the polymer dynamics in the vicinity to the solid surface. Dynamics analysis using combination of neutron and virtual experiment are presented on example of polymer brushes with grafting densities in the concentrated and semidilute regime. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S03.00010: A comparative study of nanoconfinement effects on polymer chain dynamics Shuang Jin, Gregory B McKenna We report on a study of the effects of nanoconfinement on polymer chain dynamics within the framework developed by Muthukumar [Muthukumar, M. (1991). Journal of Non-Crystalline Solids, 131, 654-666.], who suggests that there is an entropically controlled dynamical regime between the Rouse and the reptation regimes that affects the power law dependence on molecular weight of the transport properties. We have reanalyzed and compared various data from the literature for both unentangled [Hor, J. L.et al. (2018). Macromolecules, 51(14), 5069-5078..] and entangled [Shin, K., et al., Nature materials. (2007), 6(12), 961-965.] [Lange, F., et al. (2015). ACS Macro letters, 4(5), 561-565.] polymers. We find that as the confinement of the unentangled polymers becomes extreme, the chain dynamics change from those of a Rouse-like regime to those of an entropic barrier regime. For entangled polymers, the chain dynamics change from those of a reptation-like regime to those of an entropic barrier regime as polymers become increasingly confined, consistent with the Muthukumar postulate. |
Thursday, March 18, 2021 1:54PM - 2:30PM Live |
S03.00011: Ionic relaxation in ‘Solvent-in-Salt’ electrolytes Invited Speaker: Ivan Popov Solvent-in-salt (SIS) systems are one of the promising materials for the next generation of energy storage applications. The ion dynamic is significantly different in these systems from that of ionic liquids and diluted salt solutions. In this study we analyze ion dynamics of two salts Li-TFSI and Li-FSI in highly concentrated aqueous and acetonitrile solutions. We present the comprehensive study of these systems using the PFG-NMR, FTIR, QENS and MD simulations, with major focus on Broadband dielectric spectroscopy (BDS) covering the range up to 50 GHz. The estimated from the BDS data the conductivity relaxation time defines the characteristic crossover time between individual jumps of charge carriers and normal diffusion regime resulting in dc-conductivity. Analysis revealed that normal charge diffusion sets in on the distance ~1-2 Å, comparable to the average distance between the ions. Based on the idea of momentum conservation the distinct ion correlations were estimated and analyzed, and the results suggest that dependence of anion-cation correlations on solvent content. Presented analysis demonstrate that FSI based system shows faster dynamics with shorter onset of normal diffusion regime than TFSI based system resulting in higher conductivity. |
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