Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F18: Polymer Transport PhenomenaFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Doug Tree, Brigham Young University Room: McCormick Place W-184D |
Tuesday, March 15, 2022 8:00AM - 8:36AM |
F18.00001: DPOLY Invited Talk
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Tuesday, March 15, 2022 8:36AM - 8:48AM |
F18.00002: Water transport through hydrogel membranes at low relative humidities Han-Jae J Cho, Yiwei Gao, Ryan A Phung, Bianca Navarro, Genaro Marcial-Lorza, Stone Wachs Atmospheric water harvesting is an emerging research area focusing on ways to tap into the water vapor around us as a new water resource. Capturing that water vapor is thermodynamically challenging in low humidity environments. We envision a way to capture and transport that water through a thin polymeric membrane. We hypothesize that the performance of such membranes is dictated by a combination of hydrogel microstructure, hygroscopic functionalities, crosslinking, and the gradient in chemical potential. Through systematic experiments of measuring water fluxes while varying these parameters, we elucidate how transport properties such as diffusivity and permeability can be affected, especially in the context of low humidities. The results of this work will pave the way for more informed design of atmospheric water harvesting and related applications such as dehumidification. |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F18.00003: The impact of ion-ion correlated motion on salt transport in solvated ion exchange membranes Nico Marioni, Zidan Zhang, Harnoor S Sachar, Everett S Zofchak, Sanket R Kadulkar, Benny D Freeman, Venkatraghavan Ganesan Ion exchange membranes are widely used in water purification and energy generation applications to selectively and efficiently regulate salt transport, yet the influence of non-ideal ion-ion correlated motion on salt transport in these systems is often neglected and remains poorly understood. In this work, we study the impact of ion-ion correlations on salt transport in hydrated polystyrene sulfonate membranes and aqueous salt solutions via atomistic molecular dynamics simulations. Our results suggest that in both systems, cation-anion motion is positively correlated and increases significantly with doped salt concentration due to increased ion pairing. Similarly, the motion of distinct anions is found to be positively correlated and increase with salt concentration in the membrane system, but is negligible in the aqueous salt solution systems. Further, the anion diffusivities are lower than the cation diffusivities in the membrane, opposite to the trend in aqueous solution. We attribute these observations to the imbalance between the concentration of free (mobile) cations and anions in the membrane system. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F18.00004: Azo Dye Functionalization of Polycarbonate Membranes for Water Purification Sean P McBride, Ashton Caruthers, Michele Fortner, Carrie Cockerham With only 0.3% of fresh water being accessible on the surface of the Earth, having access to fresh water is a problem of global significance. Molecular dyes are used heavily in the World's growing textile industry, which contributes to roughly one-fifth of the industrial water pollution. In aqueous solutions, azo dye compounds dissociate into positive sodium ions and a negatively charged dye molecule. The research presented illustrates that polycarbonate filtration membranes with 100 nanometer diameter holes functionalized with azo dye molecules can successfully remove the negatively charged azo dye components from water. Rejection measurements are made using Ultra Violet Visible light Spectroscopy on the pre and post filtered solution. The rejection and flowrate response of filters using 3 different azo dyes separately will be presented. Using an azo dye with an intrinsic charge of -6 to functionalize a polycarbonate filter has been shown to increase rejection for the same dye by ~70% at a concentration of 50 µM. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F18.00005: Single Molecule Microscopy Informs the Design of Membrane Absorbers Ricardo Monge Neria, Spencer Schmidt, Chae Young Yoon, Maura Sepesy, Christine E Duval, Lydia Kisley Membranes are used in industrial and pharmaceutical separations due to their practical geometry and increased surface area which provide better performance compared to traditional resin-based materials. Porous membranes coated with covalently bound polymers are used to bind analytes and separate mixtures based on specific forces. However, mass transport in these systems is typically modeled and studied empirically at the ensemble level, which convolves the contributions of transport through the porous support, through the polymer, and heterogeneous adsorption at the interface. Ensemble results complicate analysis and obscure heterogeneity, hindering the design of polymers for high-precision separations of similar-sized and -charged species, such as lanthanides and actinides. In this work, we apply super-resolution fluorescence microscopy to study transport behavior at polymer-modified membrane interfaces at the single-molecule level. We develop a platform for imaging micron-thin polymer films using two different grafting methods. We utilize UV-initiated polymerization and Activators Generated by Electron Transfer – Atom Transfer Radical Polymerization (AGET-ATRP) to obtain different surface grafting densities and geometries to compare design and performance. Nanoscale imaging is achieved through Total Internal Reflection (TIRF) microscopy, and we track the diffusion of anionic dye as a model analyte. We observe heterogenous diffusion on UV-grafted polymer and membrane surfaces, comparably more homogenous behavior on AGET-ATRP grafted polymer, as well as rare, long-lasting adsorption events at the interface. We hope these studies inform the design of membrane absorbers for separations, as well as promote the use of single-molecule methods to aid in the study of bulk phenomena. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F18.00006: Understanding selective transport of same-charge ions in polymeric membranes Meng Shen, Eric Palacios, Lingchen Kong, Xitong Liu Selective transport of ions is desirable in many applications, such as water cleaning, rare-earth extraction, and battery technology. Polymeric membranes have been used to separate ions from water, and between ions of different charges, without introducing harmful chemicals to the environment. However, it remains challenging for membranes to separate ions of the same charge, such as chloride and nitrate. A physical understanding of the mechanisms of the selectivity of same-charge ions by polymeric membranes is needed for developing or inventing membranes with improved ion selectivity. Here we use molecular dynamics to investigate the transport of same-charge ions in polymeric membranes, and we elucidate the effects of ion hydration, membrane polarity and ion concentration on the partition and diffusion of same-charge ions in the membrane. The research provides insights for the dynamic research efforts to achieve precise same-charge-ion selectivity in polymeric membranes. |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F18.00007: A sub-2nm two-dimensional polymer membrane with dense functionalized nanopores for high power density osmotic power generation Baorui Cheng, Yu Zhong, Yuqing Qiu, Jiwoong Park, Suriyanarayanan Vaikuntanathan Osmotic power, electricity generated from salinity gradient, can potentially provide terawatt-hours of electricity annually around the globe. A semipermeable membrane with both high permselectivity and ionic conductance is at the basis of osmotic power generation. Here, we synthesized an ultrathin nanoporous membrane made from a two-dimensional polymer (2DP), which delivered a record high osmotic power generation density (~2000W/m2) exceeding the theoretical limit of traditional charge-based porous membranes. Our 2DP membrane was designed at the molecular level and synthesized using a novel interfacial method. The resulting membrane is less than 2nm thick and has dense sub-2nm pores decorated with phenolic hydroxyl groups. Molecular dynamics simulations suggested that the hydrogen bonding between phenolic hydroxyl groups and charged ions is responsible for the high permselectivity of the ultrathin nanoporous membrane. This work successfully utilized short-range interaction for osmotic power generation for the first time, introducing a new approach to designing high-performance osmotic power generation membranes. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F18.00008: The Effect of Miscibility Lengthscale on Ion Transport Behavior in Polymer-Mixture Electrolytes Chuting Deng, Daniel Sharon, Michael A Webb, Peter Bennington, Paul Nealey, Shrayesh Patel, Juan De Pablo |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F18.00009: Ion Solvation and Transport in Tetraglyme-based Electrolytes Chao Fang, David M Halat, Rui Wang The molecular understanding of cation transport is central to the rational design of electrolyte systems for Li-ion batteries. The transference number, t+0, is a key transport parameter that reflects the fraction of electric current contributed by the working cation relative to a reference velocity, which is usually taken to be that of the solvent. We present the molecular dynamics (MD) simulation study of a model liquid electrolyte consisting of tetraglyme and bis(trifluoromethanesulfonyl)imide (LiTFSI). Under the Onsager transport frameworks, the measured t+0 decreases with increasing amount of salt for concentration below 2 mol/kg. This behavior of t+0 is in quantitative agreement with that measured by electrophoretic NMR (eNMR). At these low salt concentrations, the cations are constantly solvated by solvent with either one or two tetraglyme molecules, where the two-chain motif dominates. At a particular electrolyte concentration, 1.8 mol/kg, t+0 approaches zero as most of the solvent molecules are in the two-chain motif, corresponding to identical values of average field-induced velocities of cations and solvents in eNMR. At concentrations above 4 mol/kg, where some cations are not solvated by solvent, we observe negative values of t+0. The clustering between ions is shown to affect the behavior of t+0 at these high salt concentrations. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F18.00010: Linking boron-polyol complexation mechanisms to selective transport in ligand-functionalized polyether membranes Matthew R Landsman, Frederick Rivers, Benjamin Pedretti, Benny Freeman, Desmond Lawler, Nathaniel A Lynd, Lynn Katz, Gregory Su Conventional water purification membranes exhibit poor rejection of small, neutral solutes such as boric acid, the primary species of boron at circumneutral pH. The development of membranes that effectively remove boron could expand our portfolio of energy-efficient water reuse technologies. Incorporation of chelating ligands in membranes to selectively sorb boric acid is a promising approach for boron removal. We demonstrate a polyether membrane platform functionalized with N-methyl-D-glucamine (NMDG), a polyol known to interact selectively with boron. The NMDG-functionalized membranes exhibit dual mode sorption and diffusion behavior due to specific interactions between boron and membrane sites. High sorption capacity of the NMDG membranes for boric acid is attributed to the buffering capacity of the amino group in NMDG, which promotes borate-NMDG complexation at neutral solution pH. Theory-guided X-ray absorption spectroscopy at the boron K-edge reveals molecular-level distinctions between specific boron-NMDG complexes (i.e., monochelate, bischelate) and informs macroscopic transport models. This research establishes fundamental structure/property rules for boron selectivity that could lead to new material designs for water purification membranes. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F18.00011: Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes Zidan Zhang, Amir Nasrabadi, Dipak Aryal, Venkatraghavan Ganesan Recent experimental results have demonstrated that polymeric ionic liquids doped with Li salts exhibit enhanced ionic mobilities and lithium ion transference numbers with increasing salt concentrations. In this study, we used atomistic molecular dynamics simulations on a model system of lithium salt-doped 1-butyl-3-methyl-imidazolium bistriflimide ionic liquids and poly(1butyl-3-methyl-imidazolium bistriflimide) electrolytes to identify the molecular mechanisms underlying such findings. Our results mirror qualitatively the experimental results on the influence of salt doping on the ion mobilities. Further, a surprisingly stronger dependence (coupling) between the lithium ion mobilities and polymer segmental dynamics is observed relative to the coupling between the anion diffusivities and polymer dynamics. We present results for ion coordination and hopping characteristics to rationalize such behaviors and identify the mechanistic origins of the properties of this emerging class of polymer electrolytes. |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F18.00012: Continuous Liquid-Liquid Extraction and In-situ Membrane Separation of Miscible Liquid Mixtures David L Speer Separation operations account for about one quarter of all in-plant energy consumption in the United States. Conventional liquid-liquid extractions require either thermal or chemical treatment, both of which have a large environmental impact and carbon footprint. Consequently, there is a great need to develop sustainable, clean methods of separating miscible liquid mixtures. The best opportunities to achieve this lie in replacing high-energy separation operations (e.g., distillation) with low-energy alternatives such as liquid-liquid extraction (LLE). One of the primary design challenges in LLE is to maximize the interfacial area between two immiscible (e.g., polar and non-polar) liquids for efficient mass transfer. Emulsifying the feed and the extractant, especially with a surfactant, offers a large interfacial area, but subsequent separation of emulsions can be energy-intensive and expensive. Thus, emulsions are typically avoided in conventional extraction operations. Herein, we discuss a novel, easily scalable, platform separation methodology termed CLEANS (Continuous Liquid-liquid Extraction And iN-situ membrane Separation). CLEANS integrates emulsion-enhanced extraction with continuous, gravity-driven, membrane-based separation of emulsions into a single unit operation which can significantly enhance extraction (by > 250% in certain cases), even for systems where the best extractants for miscible liquid mixtures are known. Utilizing the CLEANS methodology, we demonstrate continuous separation of a wide range of miscible liquid mixtures, including soluble organic molecules from oils, alcohols from esters, and even azeotropes. |
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