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 D04: Transport Phenomena in Membranes for Separations II |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Vera Bocharova, Oak Ridge National Lab Room: Room 127 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D04.00001: Identifying Gas Transport Mechanisms in Polymer-Grafted Nanoparticle Membranes Robert J Tannenbaum, Eric Ruzicka, Pablo Dean, Natalia Cislo, Zachary P Smith, Brian C Benicewicz, Sanat K Kumar Carbon capture and other gas separation processes have become prescient tools in the fight against climate change. Polymer nanocomposites have increasingly replaced distillation columns due to their smaller physical footprint and cheaper operating costs. Polymer-grafted nanoparticles (GNPs) have been investigated in this context to overcome difficulties controlling nanoparticle dispersion. GNP membranes have demonstrated a marked enhancement in gas permeability relative to the neat polymer, with this enhancement greater for larger penetrant sizes. Activation energies of transport display unique trends in grafted polymer systems as a function of penetrant size. Measurements of penetrant sorption indicate larger penetrants preferably transport via lower density interstitial regions between adjacent particles. This work aims to unpack the relationship between transport energies and their associated mechanisms in GNP systems. Changes in preparation methods can affect the underlying structural formation of the disparate polymer chain regions within GNPs. Elucidating the role of the particle surface, dense brush region, and interstitial spaces are all key to an improved mechanistic understanding. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D04.00002: Alkali halide salt partitioning in PEGDA membranes under mixed salt conditions Everett S Zofchak, Aubrey E Quigley, Jordyn G Yoh, Adit M Trivedi, Venkatraghavan Ganesan, Benny Freeman Recent efforts in membrane science have focused on incorporating ion-specific interactions into polymeric materials to bias the partitioning or diffusivity of one ionic species over others. While many notable advances have been made in this area, most studies are limited to single salt partitioning and diffusivity experiments, which may or may not accurately reflect the behavior observed in the complex mixed salt environment that these separations are employed in. In this work, we study how the presence of multiple salts influences salt partitioning into poly(ethylene glycol) diacrylate (PEGDA), a model membrane material exhibiting ion-specific interactions. We observe that at a fixed external total salt concentration, increasing the mole fraction of a non-complexing salt (e.g., LiCl) leads to an increase in the partition coefficient of that salt, in accordance with single salt partitioning experiments. Conversely, increasing mole fraction of a complexing salt (e.g., KCl) leads to a decrease in the partition coefficient of that salt. We attribute the trends for the complexing salt to a saturation of ethylene oxide binding sites within the membrane with increasing mole fraction of the complexing salt. To rationalize these experimental observations, molecular dynamics simulations are employed to reveal changes in cation binding with changing mole fraction. Our results provide fundamental insights into how partitioning trends in mixed salt environments differ from single salt environments, with important implications for industrial applications of membranes to ion-specific separations. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D04.00003: Modeling Adsorption and Transport Properties of Gases in Amorphous Polymers Micah L Welsch, Brian B Laird Developing greener and more cost-effective polymer membranes for gas separation is of major interest within the industry of gas purification, in particular with regard to H2 separation. Present findings suggest that fluorinated membranes are a promising medium for H2 gas selective separations. In this work, molecular modeling was used to aid experimental efforts to optimize fluorinated polymer membranes for high H2 permeability selectivity. Permeability is comprised of the product of solubility and diffusivity, both of which are easily accessible computationally. To guide a detailed understanding of this behavior a molecular-level approach has been applied with both Monte Carlo and molecular dynamics simulation. Gibbs-Ensemble Monte Carlo was used to calculate gas solubility and allowed for the determination of preferred adsorption sites within the polymer systems. Molecular dynamics simulation was then used to calculate rates of gas self-diffusion with each polymer studied. The fluorinated polymers examined in this study also possess differing tacticities whose unique structures were examined in hopes that they may offer an additional degree of freedom for polymer optimization. Gaining an understanding of these processes on a molecular level will help guide the optimization of polymer structures and conditions needed to develop efficient separation membranes. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D04.00004: Molecular simulation of gas solution-diffusion in polyvinylamine/polyvinyl alcohol blend membranes Kohei Sato, Daisuke Fukumitsu, Yuta Yoshimoto, Ikuya Kinefuchi Polyvinylamine (PVAm)/polyvinyl alcohol (PVA) blend membranes have been drawing attention for their gas transport performance as carbon dioxide separating membranes. In PVAm/PVA blend membranes, carbon dioxide is selectively transported by taking advantage of its reactivity to amines. Carbon dioxide molecules diffuse through the membrane by binding and unbinding to the amines in side chains of PVAm molecules continuously, resulting in relatively high permeability and permselectivity against other types of gasses. In this study, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were conducted to analyze diffusivity and solubility of carbon dioxide and nitrogen molecules in assembled PVAm/PVA membrane models. We also constructed water-added membrane models to replicate humid environments. In the MD simulations, gas molecules inserted in the models with PVAm diffused less than those in models without PVAm. Additionally, insertion of water significantly enhanced the diffusion of both carbon dioxide and nitrogen molecules. In the GCMC simulations, insertion of PVAm chains leads to decrease in the number of inserted gas molecules. However, carbon dioxide maintained a solubility higher than that of nitrogen regardless of the proportion of PVA within the system. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D04.00005: Nanoscale structure and transport in simulated polyelectrolyte membranes Ritwick Kali, Scott T Milner Polyelectrolyte membranes swell to absorb water, which forms interconnected paths that facilitate ion and water transport. Such membranes can be used for a variety of applications including electrolysis, energy storage, and water filtration. A key question about these membranes is how the polymer architecture affects the properties of the aqueous pore space and transport within it, which can be explored through well-designed simulations. Here, we investigate polystyrene-polymethylbutylene block copolymer membranes, with the polystyrene block randomly sulfonated to an experimentally relevant level (25 mol percent). We vary the amount of water in the membrane, and find strong circumstantial evidence that the equilibrium water uptake is about 16 water per sulfonate, consistent with experiments. Surprisingly, even at a water content 8x smaller, the pore structure remains connected, with geometry that shrinks down to narrow ribbons. We measure both short and long-time diffusivity of counterions and water, and find that diffusivity increases with water content. The counterion distribution in the pore space is not uniform; counterions are mainly found near the polymer-water interface, which is decorated with sulfonate anions. This non-uniform distribution may have important consequences for ion rejection described by Donnan exclusion. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D04.00006: Chain End Functionalization of Polyoxymethylene Polymer Membrane for Better CO2 Separation Yasemin Basdogan, Zhen-Gang Wang (PEO)-based polymers have been leading membrane materials for CO2/N2 separation. The ether oxygen moiety is a unique functional group that exhibits affinity towards CO2 but not N2, which leads to high CO2 solubility and CO2/N2 solubility selectivity. In this study we systematically study the effect of increasing the ether-oxygen content on a polymer's performance for the separation of CO2 from N2 and O2 gas. We study pure gas solubility and diffusivity as well as solubility and diffusivity selectivity. We use the oxygen to carbon ratio as the indicator for the ether-oxygen content in the polymer membrane. We select five polymers that have oxygen to carbon ratio from 0 to 1. We use equation of state calculations to calculate the gas solubility, and molecular dynamics simulations to calculate gas diffusivity in the polymer melt. We show that we can significantly control the CO2/N2 solubility selectivity of a memebrane material by increasing the oxygen ether content in the polymer without affecting the CO2/N2 diffusivity selectivity. We note that the highest diffusivity selectivity for both CO2/N2 and CO2/O2 gas pairs were found in the POM membrane; thus we suggest POM polymer membrane as a promising polymer for the CO2 separation from N2 and O2 gas. To increase the CO2/N2 diffusivity selectivity, we further investigate the role of the chain ending with POM polymer membrane by altering it from hydrogen to an azo (CN=CN) and triazine (nitrogen containing heterocycle) functional groups. We conclude adding nitrogen containing 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 also convert the terminal groups of POM polymers to acrylate, acetyl, and ethoxy groups and compare their CO2 separation performance. The terminal hydroxyl groups forms hydrogen bonding and reduce the chain flexibility, leading to lower gas diffusivity and permeability. Converting the terminal hydroxyl groups to acrylate, acetyl, and ethoxy groups eliminates the effect of hydrogen bonding and increases the gas diffusivity as well as the diffusivity selectivity. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D04.00007: Modeling of polyphenol filtration by polyethersulfone ultrafiltration membrane : A classical molecular dynamics study Marie Certiat, Johanne Teychene, Christelle Guigui, Stéphanie Laborie, Franck Jolibois Polyphenols are abundant in plants and their antioxidant and anti-inflammatory properties have numerous therapeutic applications. Ultrafiltration membrane processes represent an ecological and economical alternative for the extraction of polyphenols from biomass juices. However, one of the main limitations is the fouling of the membranes, the mechanism of which remains unclear. Therefore, it is essential to determine and understand the interactions in the vicinity of the membrane to improve operating conditions. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D04.00008: Characterizing penetration of a contaminant into block copolymer coatings Krishnaroop Chaudhuri, Riddhiman Medhi, Zhenglin Zhang, ZHUOYUN CAI, Anthony Malanoski, Brandy White, Christopher K Ober, Jonathan Pham Polymer coatings are critical as protective barriers and it would be beneficial to understand how the polymer properties relate to small molecule penetration into coatings. Towards this goal, we investigate how a model dye molecule penetrates into block copolymer coatings. In a typical experiment, a drop of fluorescent Rhodamine B dye solution of known concentration is placed on a coating of micron-order thickness, while confocal microscopy is used to visualize the resultant fluorescence inside the coating over time. As a starting point, block copolymers are synthesized with polystyrene (PS) blocks and modifiable polydimethylsiloxane (PDMS) blocks. Using image analysis methods, we track the temporal and spatial fluorescence distribution in the coating. A model based on first principles is developed to determine the rate of penetration; we find that the rate of dye penetration into the coating is a function of the initial dye concentration and the PDMS content in the block copolymers. Ultimately, we expect that a better understanding of how small molecules penetrate into polymers will help guide the design of more effective coatings for a wide range of applications. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D04.00009: Molecular modeling of toxic industrial chemicals (TICs) in metal organic framework (MOF) filtration Adam R Hinkle, Matthew Browe, Ivan O Iordanov Toxic industrial chemicals (TICs) are hazardous substances regularly produced and transported in industrial and agricultural settings in abundance throughout the world. They are well known to be serious respiratory threats and are often poorly removed by current filtration media using activated carbon found in many types of personal protective equipment. Metal-organic frameworks (MOFs) hold great promise as a single material candidate for next-generation filtration media. In this talk we report on molecular dynamics calculations designed to model the dynamic behavior of TIC-MOF interactions. The effects of water, solution chemistry, pH, modulator inclusions, and their role in the behavior of high priority TICs, e.g., ammonia and sulfur dioxide, are examined using available reactive forcefields. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D04.00010: Impact of dynamical correlations on salt transport in solvated ion exchange membranes Nico Marioni, Akhila Rajesh, Zidan Zhang, Everett S Zofchak, Harnoor S Sachar, Sanket R Kadulkar, Benny D Freeman, Venkatraghavan Ganesan Ion exchange membranes are widely used in water purification and energy storage applications to selectively and efficiently regulate salt transport, yet the influence of dynamical ion-ion correlations and ion pairing/condensation on salt transport in charged polymer membranes remain poorly understood. In this study, we use the framework of Onsager transport coefficients within atomistic molecular dynamics simulations to study the impact of ion-ion correlated motion on salt transport in experimentally relevant hydrated polymer membranes. At sufficiently high salt concentrations, cation-anion dynamical correlations exert a significant influence on both salt diffusivities and conductivities. Anion-anion distinct correlations, arising from the imbalance between the concentration of free (mobile) cations and anions, and the retarding effect of the fixed charge groups on cations, proves to be an additional important feature for charged membranes. Our results demonstrate that dynamical correlations should become an important consideration in experimental measurements of salt diffusivities and conductivities for non-dilute salt solutions in polymer membranes. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D04.00011: Simplified Model for Penetrant Hopping through Polymer Grafted Nanoparticles Willliam C Marshall, Robert J Tannenbaum, Sinan Keten, Sanat K Kumar Polymer grafted nanoparticles (GNPs) have enhanced gas transport properties compared to those of neat polymer matrices, which are often used in industrial separations. Activation energy of penetrant transport in GNPs exhibits a uniquely segmented trend compared to the single unifying trend found in neat polymer melts. These two distinct trends in the GNP systems alludes to possible differences in the transport mechanism of variously sized penetrants. The proposed mechanism for GNP membrane transport is hypothesized to stem from microscopic structure of GNPs with high grafting density and intermediate graft lengths. In this work, we investigate the proposed mechanism of hopping by constructing a simplified hard sphere Monte Carlo model, from which activation energy trends are successfully reproduced at little computational expense. Our results allow the mapping of parameters with physical significance to experimental materials, such as the molecular stiffness of a monomer, which permits us to compare materials from these properties, as well as provides the ability to track particle movement as a function of its size. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D04.00012: Shape-selective filtration of nanomaterials and proteins using lamellar block copolymer-based slit membranes Alamgir Karim The growing need for highly efficient water purification and bioseparations necessitates innovations in block copolymer (BCP) based ultra-filtration membranes. Most of the work in BCP membranes has focused on using cylindrical pores. However, biological ultrafiltration membranes can have complex architectures which can perform complex separations. In this work, we demonstrate novel slit-based membranes using lamellar block copolymers by taking insights from biological membranes. The vertically oriented BCPs are converted to slit membranes using a wet etching process. These slit-shaped membranes demonstrate sharp cut-offs for solute filtration. Furthermore, we demonstrate the first example of enhanced separation of 1-D nanomaterials (nanorods) as compared to the 0-D nanomaterials (nanoparticles) using these slit-based membranes, which is facilitated by the shape similarity of 1-D nanomaterials with the nano-slits. Additionally, we show that these slit-shaped membranes show 100 % permeability of similar-sized Lysozyme and Bovine Serum Albumin (BSA) proteins while retaining the Immunoglobulin G (IgG) antibodies up to 70 %, thus making them highly useful for bioseparations. The enhanced permeation of the BSA and Lysozyme is governed by their relative one-dimensional shapes as opposed to the Y-like shape of the IgG proteins. We believe that these slit-shaped membranes will be useful for shape-selective filtrations across a spectrum of applications. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D04.00013: Understanding the high Cl-/ F- permselectivity of random zwitterionic amphiphilic copolymer (r-ZAC) membranes Harnoor S Sachar, Zidan Zhang, Nico Marioni, Everett S Zofchak, Venkatraghavan Ganesan Random zwitterionic amphiphilic copolymer (r-ZAC) membranes have shown tremendous promise for facilitating ionic separation processes by virtue of their tunable morphology. Recent experiments reveal exceptionally high NaCl/NaF permselectivity for r-ZAC membranes with sub-nanometric zwitterionic pores. This is a result of the simultaneously higher solubility and diffusivity of NaCl (as compared to NaF) within these membranes, thereby circumventing the solubility-diffusivity tradeoff. We conducted molecular dynamics simulations to probe the transport of NaCl and NaF in r-ZAC membranes with varying pore morphologies (achieved by varying the water volume fraction). Our results indicate that the lower self-diffusivity of F- ions (relative to Cl- ions) within r-ZAC membranes stems from a higher dielectric drag acting on the F- ions. The reduction in dielectric constant of water in conjunction with the sluggish re-orientational dynamics of water dipoles exacerbates the impact of dielectric drag in dictating ionic diffusivity within the membrane. Reduction of the water volume fraction leads to nonmonotonic variation in the Cl-/ F- diffusivity selectivity due to a complex interplay between the Stokes drag, dielectric drag, membrane-ion interactions and morphology-induced nanoconfinement. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D04.00014: Gas transport through glassy polymer membranes from all-atom molecular dynamics simulations Janani Sampath Polymers are attractive membrane materials owing to their mechanical robustness and relatively inexpensive fabrication. An important feature central to polymer membrane performance is the distribution of connected void spaces created by inefficient packing of bulky groups on the polymer backbone, known as free volume elements (FVEs). FVEs tend to degrade over time as polymer chains reorganize irreversibly; relating local chain dynamics to the distribution of FVEs can help control phenomena like plasticization and aging. In this work, we use atomistic molecular dynamics simulations to study three polymers - polymethylpentene (PMP), polystyrene (PS), and HAB-6FDA thermally rearranged polymer (TRP). These polymers represent a broad range of structures, allowing us to understand the interplay between polymer chemistry and membrane function. We compute FVEs by identifying filled and free regions in the membrane, as well as atoms that lie on the surface separating the two regions. We find that polymer segments near the surface of voids exhibit faster dynamics compared to bulk segments. This dictates the stability of FVE distribution across different polymer chemistries, serving as a predictor for membrane aging and plasticization. To compute the permeation of gas mixtures such as olefins and paraffins through the membrane matrix, we use the non-equilibrium concentration gradient method. The results from this approach are compared against experimental techniques that measure permeation. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D04.00015: Thermodynamics of Ionic Bonding with Crown Ethers Ramón González-Pérez, Stephen Adams, William A Phillip, Jonathan K Whitmer Lithium resources are limited, and the recent increases in demand and a general desire for less energy intensive, more environmentally responsible processes have lead to increased interest in lithium recycling methods. Multiscale processes studies linking molecular properties, device design decisions and process system optimization are needed to develop effective separation systems. Our long-term interest is in improving membrane technologies used to separate Li+ in brines. By using polymeric membranes functionalized with unique ligands, ions can be captured via host-guest interactions. Thus, in this work, we approach the molecular properties side of this multiscale study by performing Molecular Dynamics simulations of specific hosts—crown ethers—in aqueous solutions. Three different crown ethers were selected in order to understand their binding affinity and the mechanics with which they bind to Li+ and Na+, a typical competitor ion in brines. Free energy calculations with umbrella sampling were used to compute the potential of mean force PMF of each system. We report on the relative efficacy of binding for these ions and its implications for the design of lithium separation membranes. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700