Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K18: Transport Phenomena in Polymers and Polymer Membranes IIFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Daniel Hallinan, FAMU-FSU Room: McCormick Place W-184D |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K18.00001: DPOLY Invited Talk
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Tuesday, March 15, 2022 3:36PM - 3:48PM |
K18.00002: Design-driven trends in transport properties of artificial water channels Ritwick Kali, Scott T Milner Peptide-appended pillar arenes (PAP) are a family of tubular molecules that allow rapid and selective transport of water. These artificial water channels embedded in self-assembled polymer bilayers can serve as desalination membranes, with potential for reverse osmosis because of their rigid pore dimension and favorable surface chemistry. In this work, we use atomistic molecular dynamics simulations to study the water mobility and ion rejection characteristics of a range of PAP channels with varying tube diameter, embedded in self-assembled polybutadiene-polyethylene oxide membranes. From our prior work, we know that PAP channels reject ions through hydration shell stripping. An ion must partially dehydrate to be able to pass through the narrow pore; this incurs a significant free energy penalty, so the pore is able to reject ions. As the pore diameter increases, the water mobility goes up, while the ion rejection drops. By our simulations, we determine the limiting size of the PAP channel that offers enhanced water transport while still rejecting ions. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K18.00003: Tuning Ether Motifs in Polymers Membranes for Carbon Capture Yasemin Basdogan, Zhen-Gang Wang Polymer membranes suffer from design challenges due to the negative correlation between two principal features of separation performance (permeability and selectivity). In this project, we study the effect of increasing ether oxygen content in the polymer membrane. We investigated five different polymer materials that range in O:C ratio, including polyethylene (PE, O:C=0), polytetramethylene oxide (PTMO, O:C=0.25), polyethylene oxide (PEO, O:C=0.5), poly(1,3-dioxolane) acrylate (PDXLA, O:C=0.67), and polyoxymethylene (POM, O:C=1). Molecular dynamics simulations showed POM has higher CO2/N2 and CO2/O2 selectivity compared to the commonly used PEO. Additionally, we studied the effect of adding N2 phobic functional groups to the ends of POM polymer membrane. Adding functional groups to the chain ends of the polymer significantly slows down the gas diffusion thus makes these polymer membranes not optimal candidates for neither CO2/N2 nor CO2/O2 separation. We have also studied the effect of temperature on the gas diffusion in POM polymer membrane. We have showed that the gas diffusion increases with increasing temperature; however, the diffusion selectivity decreases for both CO2/N2 and CO2/O2 separation. Our future efforts will focus on studying gas diffusion in polymer mixtures. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K18.00004: Modeling microstructure formation in block copolymer membranes using dynamical self-consistent field theory Douglas Grzetic, Anthony J Cooper, Alexander T Bridge, Kris T Delaney, Glenn H Fredrickson, Benny D Freeman Block copolymers have attracted recent interest as candidate materials for ultrafiltration membranes, due to their ability to self-assemble an isoporous selective layer at the membrane surface. However, the dependence of surface layer and substructure morphologies on the many processing variables for block copolymer membranes is not well understood. Here, we use dynamical self-consistent field theory to simulate the microstructure evolution of block copolymer membranes during the phase inversion process. In particular, we find that the block selectivities of the solvent and nonsolvent dramatically affect the resulting microstructure. We discuss the implications of the observed trends on the choices of solvent and nonsolvent in the processing context. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K18.00005: Origins of cation-cation selectivity in crown ether-functionalized polymer membranes Everett S Zofchak, Zidan Zhang, Nico Marioni, Tyler J Duncan, Harnoor S Sachar, Benny D Freeman, Venkatraghavan Ganesan Selective separation of monovalent cations from complex mixtures is an industrially relevant procedure necessary for the recovery of many commodity materials, such as lithium from salt brines. Unfortunately, most conventional membranes lack selectivity between monovalent ions, rendering their use in such applications infeasible. One approach to overcoming selectivity limitations is to incorporate ligands into membranes which specifically interact with target cations in an aqueous environment. In this work, we assess how incorporating crown ethers, which form host-guest complexes with monovalent cations, into poly(norbornene) networks impacts the selective partitioning and diffusion of alkali cations. For the case of a 12-Crown-4-functionalized membrane, atomistic molecular dynamics simulations reveal a strong coupling between cation hydration and their sorption and diffusion in the membrane. More specifically, we observe that alkali cation complexation tends to increase with decreasing cation hydration free energy. This complexation is observed to generally enhance salt partitioning, but decrease salt diffusivity. To rationalize these observations, we develop an approximate model which is able to qualitatively explain the trends observed in simulations. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K18.00006: Molecular Simulations of Water Vapor Adsorption in Hygroscopic Polymer-Solvent Mixtures James H Zhang, Shaoting Lin, Xuanhe Zhao Advanced polymer-based desiccants have the ability to adsorb water vapor for dehumidification and atmospheric water harvesting applications. Molecular simulations are conducted to study water vapor adsorption in pure polyacrylamide and polyacrylamide-glycerol mixtures. Molecular dynamics and Monte Carlo simulations are used to elucidate the coupling behavior between vapor adsorption and polymer chain structures at 298 K. The polymer chain conformations, radial distribution functions, and pore size distributions in the polymer are analyzed to understand the effects of glycerol and water on plasticizing the polyacrylamide. The effects of adsorption induced swelling is seen to have a large effect on the adsorption isotherms of polymer systems, especially in the higher relative humidity range. The addition of glycerol leads to the polyacrylamide to have a more swollen initial state before adsorption and enhance vapor adsorption due to its high hygroscopy. |
Tuesday, March 15, 2022 4:36PM - 4:48PM |
K18.00007: Preferential Transport of Divalent Ions through PEDOT:PSS Membranes and Coatings Njideka Nnorom, Tanya K Rogers, Amit Jain, Abdullah Alazmi, Welman C Elias, Michael S Wong, Rafael Verduzco There is a need for polymeric membranes and processes with selectivity towards specific salts or counterions. This would lower the cost for recovery of valuable ions such as lithium or copper and enable more cost-effective approaches to the removal of scalants and toxic ionic contaminants such as nitrates and phosphates. Here, we demonstrate that the commercial conductive and sulfonated polymer PEDOT:PSS can be used to significantly enhance the selectivity for removal of divalent counterions in a membrane capacitive deionization (MCDI) process. PEDOT:PSS represents a useful model material because the sulfonate functionalities provide preferential permeability to divalent ions and the crosslink density and water content of swollen membranes can be systematically tuned. We characterize the physical and transport properties of PEDOT:PSS and incorporate it as an ion-selective layer in an MCDI system. We show that preferential transport of Ca2+ over Na+ can be attributed to a higher membrane diffusivity of Ca2+ in the membrane. The use of the PEDOT:PSS ion exchange membrane increases ion selectivities from 2:1 to 10.5:1 under optimized conditions. This work demonstrates a new and readily available polymeric material for selective extraction of divalent ions. |
Tuesday, March 15, 2022 4:48PM - 5:00PM |
K18.00008: Modeling the Self-assembly of Block Copolymers Upon Solvent Evaporation in Thin Films with Dynamical Self-consistent Field Theory Anthony J Cooper, Douglas Grzetic, Alexander T Bridge, Kris T Delaney, Glenn H Fredrickson, Benny Freeman The evaporation of solvent from a block copolymer solution is a method widely used to self-assemble block copolymers in thin films. Due to a vast parameter space and the nonequilibrium nature of the evaporation process, reliably generating well-ordered structures remains a great challenge. We use Dynamical Self-consistent Field Theory (DSCFT) to model the evaporation of a diblock copolymer solution by controlling the rate of solvent diffusion out of the film. The effect of tuning parameters such as solvent volatility, solvent selectivity towards one of the blocks, and block copolymer composition on the self-assembly is investigated. |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K18.00009: Simulating chemical transport in functionalized polymer-particle composites Adam R Hinkle, Matthew A Browe, Mark J Varady Improved chemical resistance of polymer-based coatings remains a significant challenge for many defense applications and technologies. In particular, composites with high concentrations of large, micron-size particles present a complex microstructural landscape of competing processes which influence the transport of penetrant molecules. In this talk we report on molecular dynamics calculations designed to model particle surfaces that have been modified by the addition of functional groups. The effects of the functionalized surfaces on the surrounding polymer binder and the diffusive transport of penetrant molecules is examined for different chemistries. We directly calculate penetrant diffusion coefficients and polymer-penetrant properties within an identifiable interfacial region in the composite, and quantitatively compare with simulations of transport in the bulk systems. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K18.00010: Microscopic theory for the activated dynamics of molecules in polymer melts and crosslink networks Baicheng Mei, Kenneth S Schweizer We construct a microscopic force level theory for the activated dynamics of dilute molecules of variable shape in dense polymer melts and crosslinked networks. Based on the elastically cooperative nonlinear Langevin equation theory of structural relaxation, the polymer matrix glass transition temperature (dynamic fragility) increases with (is largely independent of) crosslink density, trends which strongly impact penetrant motion. At fixed temperature with increasing crosslink density, the penetrant mean hopping time (or inverse diffusion constant) grows exponentially, and the degree of molecule and polymer alpha time decoupling varies in a nonmonotonic manner. These trends are robust to changing molecular shape and size, albeit with important quantitative differences. Predictions of the theory for the diffusion of an elongated aromatic penetrant in tightly crosslinked networks as a function of degree of crosslinking and temperature are in good agreement with recent experiments and simulations. Overall, the theoretical results as a function of penetrant size and shape, temperature, and degree of crosslinking provide insights concerning how to optimize the absolute and relative (selectivity) diffusion rates relevant to polymer-based membrane separations. |
Tuesday, March 15, 2022 5:24PM - 5:36PM |
K18.00011: Impact of ionic correlations on the selective transport of salts through polymer membranes Harnoor S Sachar, Nico Marioni, Everett S Zofchak, Zidan Zhang, Sanket R Kadulkar, Tyler J Duncan, Venkatraghavan Ganesan Polymer membranes can be utilized for ionic separation through the incorporation of host-guest interactions. This is achieved via selective binding of the polymeric functional groups with a particular ionic species in a mixture, thereby altering the relative solubility and diffusivity of the ions within the membrane. We employ molecular dynamics simulations to probe the effect of membrane chemistry and feed composition on the diffusivity selectivity of salts in a binary mixture. Furthermore, the diffusivity selectivity for binary mixed salt systems is compared to that obtained from corresponding single salt systems. We utilize the Onsager framework to quantify the impact of ionic correlations on salt transport within the membrane. We show that ionic correlations can lead to significant deviations of salt diffusion from ideality. Our parametric study helps identify the conditions under which ionic correlations become dominant and therefore cannot be neglected during experimental estimation of salt diffusivity. The results from this work will aid in design of polymer membranes with high ion-specific selectivity. |
Tuesday, March 15, 2022 5:36PM - 5:48PM Withdrawn |
K18.00012: Gas Diffusion in Polymer-Grafted Nanoparticle Melts Arash Nikoubashman, Elias M Zirdehi, Jiarul Midya, Michael Rubinstein, Sanat K Kumar Polymer-grafted nanoparticles (PGNPs) are interesting candidates for gas separation applications owing mainly to the heterogeneous dynamic environment they provide for different gas components. To engineer the selectivity of these materials, it is crucial to understand the distribution and dynamics of the permeating gases. To this end, we use coarse-grained molecular dynamics simulations, systematically varying the size of the gas particles as well as the grafting density and chain length of the PGNPs. We track the motion of the individual gas particles, finding spatially heterogeneous dynamics, associated with the strong coupling between gases and the grafted polymers. In addition, we discuss possible scenarios of optimizing selectivity by manipulating the heterogeneous transport environment upon the addition of homopolymers of different lengths. |
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