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 B04: Transport Phenomena in Membranes for Separations IFocus
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Sponsoring Units: DPOLY Chair: Lilin He, Oak Ridge National Lab Room: Room 127 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B04.00001: Exceptionally Fast Ion Diffusion in Porous Carbon Fibers Derived from Block Copolymers Invited Speaker: Guoliang Liu Confined ionic liquids in hydrophilic porous media have disrupted lattices and can be divided into two layers: An immobile ion layer adheres to the pore surfaces, and an inner layer exhibits faster mobility than the bulk. In this work, we report a study of ionic liquids confined in block copolymer-based porous carbon fibers (PCFs) synthesized from polyacrylonitrile-block-polymethyl methacrylate (PAN-b-PMMA). The PCFs contain a network of unimodal mesopores of 13.6 nm in diameter and contain more hydrophilic surface functional groups than previously studied porous carbon. Elastic neutron scattering shows no freezing point for 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) confined in PCFs down to 20 K. Quasi-elastic neutron scattering (QENS) is used to measure the diffusion of [BMIM]BF4 confined in PCFs, which, surprisingly, is 7-fold faster than in the bulk. The unprecedentedly high ion diffusion remarks that PCFs hold exceptional potential for use in electrochemical catalysis, energy conversion, and storage. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B04.00002: Polymer dynamics and the performance of amine containing polymers for separating carbon dioxide from the ambient atmosphere Christopher L Soles, Avery E Baumann, John R Hoffman, Christopher M Stafford, Takeshi Yamada, Kanae Ito, Craig M Brown Polymer membranes and sorbents are an important component of direct air capture strategies for removing carbon dioxide (CO2) from the ambient atmosphere. Branched polyethylimeimine (PEI) is one of the most popular aminopolymer sorbents being used for CO2 capture applications. However, fundamental knowledge about the CO2 adsorption/desorption mechanisms as a function of temperature, humidity, and amine population in PEI are critically needed to develop improved CO2 sorbents. While many studies to date have focused on CO2 sequestration performance of PEI or derivatized composites, very few have examined polymer-sorbate interplay and resulting effects of sorption on dynamics. In this presentation, we demonstrate that quasielastic neutron scattering (QENS) is useful to probe dynamics before and after exposure to water and/or CO2. We found that each dosing condition, as well as the nature of the amine groups, separately influences diffusive behavior. The results from QENS experiments are coupled with findings from other physiochemical characterization methods to provide a holistic view of molecular sorption in PEI. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B04.00003: Effect of Film Thickness and Temperature on the CO2 Sorption in Poly(ethyleneimine) Christopher M Stafford, John R Hoffman, Avery E Baumann Poly(ethyleneimine) (PEI) is an attractive material for CO2 soprtion due to its high amine content (1 nitrogen for every 2 carbons). Hyperbranched PEI, specifically, is appealing due to its low glass transition temperature (Tg), which facilitates diffusion of CO2 through the polymer. However, due to its low Tg hyperbranched PEI is typically imbibed into porous silicates to form a solid sorbent material. This coating process, while practical, leads to poorly defined PEI film thickness and local variations in PEI concentrations within the porous support. In an effort to understand fundamental aspects of CO2 uptake and release, we proposed to study planar PEI thin films, which allows us to explore the effect of film thickness on CO2 sorption. In this presentation, I will discuss our measurements of adsorption/desorption at a function of temperature, humidity, and CO2 concentration for different PEI film thicknesses using tandem quartz crystal microbalance (QCM) and polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS). Coupling these techniques allows for quantification of mass uptake via QCM and spectral identification of reaction products via FTIR. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B04.00004: Monovalent Ion Selectivity of Cellulose Acetate Membranes Paul R Irving, Kevin K Reimund, Everett S Zofchak, Nico Marioni, Harnoor S Sachar, Zidan Zhang, Benny D Freeman, Venkatraghavan Ganesan Increasing demand for lithium requires improved methods for extraction from brine. Magnesium contamination is associated with low yield in traditional production processes. Polymer membranes offer a potential alternative for selectively enriching lithium. Using dense cellulose acetate membranes, our experiments indicate a remarkably high lithium/magnesium permeability selectivity on the order of 500:1. The reported selectivities of asymmetric reverse osmosis, nanofiltration, and selective electrodialysis membranes are typically less than 50. Further, our experiments demonstrate that the high selectivity of cellulose acetate is attributed primarily to differences in salt diffusivity rather than solubility. We produce atomistic molecular dynamics simulations that support the observed diffusion selectivity. Higher charge of magnesium relative to lithium is found to result in an increase in dielectric drag, higher ion pairing, and more water clustering around the cation. These observations are used to explain the observed experimental trends. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B04.00005: Aperiodic Percolated Nanostructures in Hydrated Fluorine-free Terpolymers for Proton Exchange Membranes Max Win, Karen I Winey, Amalie L Frischknecht Fluorine-free polymers with mechanical and transport properties rivaling or exceeding that of perfluorosulfonic acid polymers are sought for hydrogen fuel cells. This work expands upon a recent study that investigated the proton transport properties of a precise polyethylene with phenylsulfonic acid branches on every fifth carbon. Novel terpolymers with a range of ion-exchange capacties (IEC) could be synthesized by copolymerization and varying the degree of sulfonation on pendant phenyl groups. We applied atomistic molecular dynamics simulations to explore this vast compositional space of terpolymers consisting of segments of five-carbon polyethylene, five-carbon polyethylene with a phenylsulfonic branch, and five-carbon polyethylene with a phenyl branch. Under hydration, many of the terpolymers exhibit strong nanophase separation into polymer and water domains due to the flexible carbon backbone. The diffusion coefficient of the hydronium ion decreases with IEC as the percolated water channels become more tortuous. Fractal dimensional analysis of the nanostructured material correlates well with the normalized water diffusion coefficient. Finally, bounds for hydrogen-conducting compositions for this terpolymer are established via the investigation of mean-squared displacements.
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Monday, March 6, 2023 12:54PM - 1:06PM |
B04.00006: Monovalent Cation Selectivity in Ion Exchange Membranes Near the Percolation Threshold Marshall C Tekell, Sanat K Kumar, Yuxuan Huang, Jingchao Qin, Ngai Yin Yip Structure-property relationships in ion-exchange membranes (IEMs) have been developed to understand the trade-off between membrane conductivity and selectivity toward the counter-ion (e.g. Na+ in cation IEMs). Engineering membranes with high-selectivity toward counter-ions of the same valence, however, remains an open challenge in the field. In this work, we leverage differences in the hydrated radii and hydration free energies of monovalent cations (Li+, Na+, K+) to engineer cation exchange membranes with tunable selectivity. We control the sulfonation level (SL) of polystyrene-r-sulfonated polystyrene (PS-r-SPS) copolymers and neutralize these random copolymers with Li+, Na+, and K+ cations. Using a combination of wide-angle x-ray scattering (WAXS), ion-exchange capacity (IEC), swelling degree (SD), and conductivity measurements, we find a critical ion cluster percolation threshold below which membranes are unable to exchange ions with the external electrolyte. In turn, this percolation threshold determines the minimum required water volume fraction in the hydrated membrane. Mixed-salt permeation experiments conducted for membranes just above the required show favorable transport to K+ relative to Li+. We attribute the favorability for transport at this lower limit of membrane hydration to the difference in hydration free energy between the two ions. Thus, we demonstrate that a fundamental, intrinsic property of CEMs (i.e. hydration) can be manipulated to achieve novel separations and that membrane topology (i.e. percolation threshold) limits the exploitation of the difference in hydration free energy. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B04.00007: Ionic drug transport in charged biosponge polymers to reduce chemotherapy toxicities Hee Jeung Oh Cancer is becoming the leading cause of death in most developed nations. Despite efforts to develop targeted and personalized cancer therapeutics, dosing of the cancer chemotherapeutics is limited by toxic side effects. Typically, more than 50-90% of the injected drug is not trapped in the target organ and bypasses the tumor to general circulation, causing toxicities in distant locations. Currently we do not have any routes to remove these untrapped toxic chemotherapy drugs other than relying on the body’s natural metabolism. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B04.00008: Ln(III) Selectivity in Biomimetic Ligand-appended Channels Tyler J Duncan, Harekrushna Behera, Laxmicharan Samineni, Manish Kumar, Venkatraghavan Ganesan Modern lanthanide separations through solvent-solvent processes are a major source of waste and come at large thermodynamic cost while sporting relatively low selectivities. With exponential demand for lanthanide resources in energy efficient lighting, permanent magnets, and electronics, the virtually identical set of 14 f-block elements is a necessary front in energy efficient membrane separations. While dawning applications for biological water channels in forward water and resource recovery processes fall short due to thermal instabilities, the synthetic pillar[n]ene template provides a wide parameter space for design based on chemistry, ligand length, bilayer composition, and sequence to mimic the biologically optimized conductivities and selectivities found in AQP (O(109) H2O/channel/s, 109 H2O:Na+) and KcsA (107 ions/channel/s, 104 K+:Na+). In this work, we offer a mechanistic insight into lanthanide-lanthanide separations in angstrom scale, transmembrane channels through molecular dynamics simulations and potential mean force calculations. The resulting conductivity measurements, energetic profiles, and coordination structures provide insight into pillar[n]ene monovalent/divalent rejection, trivalent selectivity, and water conductivity. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B04.00009: Gas Diffusion Mechanism in Two-Dimensional Lamellar Membranes Musen Chen, Maxim Trubianov, Pengxiang Zhang, Qian Wang, Zelong Li, Kostya S Novoselov, Daria V Andreeva Two-dimensional (2D) materials, e.g., graphene oxide (GO), covalent organic frameworks (COF), based lamellar membranes have shown outstanding gas separation properties, surpassing upper bound for polymeric membranes especially in hydrogen separation. However, it is challenging to directly and accurately measure gas diffusion coefficients in such ultra-thin laminated membranes. As a result, the gas diffusion mechanism therein remains unclear due to lack of diffusivity and discussion of thickness dependent gas separation properties reported in the literature. In this work, the authors developed a time lag method to determine the individual diffusivities of mixed gases in 2D lamellar membranes by on-line mass spectrometry. Pure gas and equimolar (H2/CO2) mixture tests were conducted on GO membranes. The dependence of diffusivity on membrane thickness, temperature, pressure and GO flake size was studied. The temperature and thickness dependence of diffusivities showed good agreement with thickness dependent diffusion activation energy calculated based on molecular sieving model. A two-pathway model (inter-sheet and inner-sheet) was used to explain the obtained results. This study provides an insightful roadmap for the design of other new 2D lamellar membranes. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B04.00010: Effect of Surface Modification on Polymer Diffusion in Convex Lens-induced Confinement (CLiC) Brittany K Roopnarine, Kevin Maxwell, Svetlana Morozova In water purification processes, typical membrane foulants are flexible polymers such as dextran. Understanding how dextran diffuses in confinement can help reduce fouling of membranes and lead to better separation processes overall. Here, we have determined the diffusion, D, of dextran (500,000 g/mol) in Convex Lens-induced Confinement (CLiC) using differential dynamic microscopy (DDM). In this geometry, the confinement ranges continuously from 0.085-21.7 μm. The lens and coverslip was chemically modified with perfluorodecyltrichlorosilane (FDTS) via molecular vapor deposition (MVD). The solution was then stabilized with a non-ionic surfactant, Triton X-100, which segregates at the interface between the water phase and glass to promote wetting. The dextran diffusion was measured near these stabilized surfaces and compared to the diffusion on unmodified surfaces. The dextran diffusion remained consistent for both the modified and unmodified surfaces, however in strong confinement, while hydrophobic interactions slowed the dextran diffusion near a glass surface, no effect was observed near a hydrophic surface stabilized by a non-ionic surfactant. These findings indicate the influence surface chemistry has on the diffusion of flexible polymers in confinement and can lead to a better understanding of separation processes. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B04.00011: Fundamentals of Ion Transport in Ion Containing Membranes Rahul Sujanani, Oscar Nordness, Seamus D Jones, Benny Freeman, Rachel A Segalman Ion transport in polymer electrolytes is of significant interest in various applications (e.g., water purification, electrochemical cells, and batteries). However, these communities have evolved independently, leading to a lack of design rules applicable under broad process conditions. To connect the various, disparate communities interested in polymer electrolytes, this presentation focuses on measurements and modeling of ion transport in ion containing polymers. Ion pairing is shown to greatly enhance salt sorption in hydrated ion exchange polymers due to reduced Donnan exclusion. Although ion pairing is discussed extensively in dry polymers, this phenomenon is rarely considered in hydrated polymers. Thus, predictions made using established theories for hydrated polymers deviate from the data by over an order of magnitude. Remarkably, by reformulating these models to account for ion pairing, predictions of salt sorption are significantly improved, and, in some cases, good quantitative agreement is observed between theory and experiment using no adjustable parameters. Finally, the applicability of various models for ionic conductivity in polymer electrolytes is determined as a function of water activity, demonstrating the importance of hydration on the physics of ion transport. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B04.00012: Gas Transport Properties of Polymer-Grafted Nanoparticles with Dense Polymer Brushes Natalia A Cislo, Robert J Tannenbaum, Eric Ruzicka, Brian C Benicewicz, Sanat K Kumar Polymer-grafted nanoparticle (GNP) membranes have become increasingly relevant materials for efficient size-based separation of gas mixtures in industrial processes. Membranes composed of these grafted particles have demonstrated higher gas permeability and more tunable selectivities relative to the neat polymer systems. Previous experimental and computational work led to the development of a two-layer model, representing the grafted polymer around the nanoparticle as distinct dry and interpenetration layers. However, the role in gas transport that each layer has in this model is not well understood. In our work, we study the effect of increased graft density in the dry zone on poly(methyl acrylate)-grafted-silica nanoparticles via permeation and scattering techniques. Silica surface interactions, dry zone stretching, and interpenetrated chains all contribute to a greater understanding of the transport mechanism in these systems. We find that bimodal dense brushes impact the motion of disparate penetrant sizes to varying degrees, i.e. significantly depressing light gas transport while having a minimal effect on larger penetrants. |
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