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NASA NTRS1977

Polymeric membrane systems of potential use for battery separators

Two membrane systems were investigated that may have potential use as alkaline battery separators. One system comprises two miscible polymers: a support polymer (e.g., polyvinyl formal) and an ion conductor such as polyacrylic acid. The other system involves a film composed of two immiscible polymers: a conducting polymer (e.g., calcium polyacrylate) suspended in an inert polymer support matrix, polyphenylene oxide. Resistivities in 45-percent potassium hydroxide and qualitative mechanical properties are presented for films comprising various proportions of conducting and support polymers. In terms of these parameters, the results are encouraging for optimum ratios of conducting to support polymers.

Philipp, W. H.↗

NASA NTRS1996

Solutocapillary Convection Effects on Polymeric Membrane Morphology

Macro voids are undesirable large pores in membranes used for purification. They form when membranes are cast as thin films on a smooth surface by evaporating solvent (acetone) from a polymer solution. There are two un-tested hypotheses explaining the growth of macro voids. One states that diffusion of the non-solvent (water) is solely responsible, while the other states that solutocapillary convection is the primary cause of macro void growth. Solutocapillary convection is flow-caused by a concentration induced surface-tension gradient. Macrovoid growth in the former hypothesis is gravity independent, while in the latter it is opposed by gravity. To distinguish between these two hypotheses, experiments were designed to cast membranes in zero-gravity. A semi-automated apparatus was designed and built for casting membranes during the 20 secs of zero-g time available in parabolic aircraft flight such as NASA's KC-135. The phase changes were monitored optically, and membrane morphology was evaluated by scanning electron microscopy (SEM). These studies appear to be the first quantitative studies of membrane casting in micro-gravity which incorporate real-time data acquisition. Morphological studies of membranes cast at 0, 1, and 1.8 g revealed the presence of numerous, sparse and no macrovoids respectively. These results are consistent with the predictions of the solutocapillary hypothesis of macrovoid growth.

Krantz, William B.↗

DOE OSTI2020

Polymeric membranes for separation of gases

Membranes, methods of making the membranes, and methods of using the membranes are described herein. The membranes can comprise a gas permeable support layer, optionally an inorganic layer disposed on the support, and a selective polymer layer disposed on the inorganic layer. In some cases, the selective polymer layer can comprise an amine-containing polymer and an amino acid salt dispersed within the amine-containing polymer. In other cases, the selective polymer layer comprises a sterically hindered amine-containing polymer, such as a sterically hindered derivative of polyvinylamine. The membranes can be used, for example, to separate gaseous mixtures, such as flue gas.

Ho, W.S. Winston↗

DOE OSTI2022

Computational Prediction of Water Sorption in Facilitated Transport Membranes

Polymeric facilitated transport membranes (FTMs) have emerged as an innovative class of promising carbon capture technology. Studies have shown that the transport properties of an FTM are significantly influenced by its water uptake. In order to better quantify FTM performance, we herein explore the potential of computational techniques to predict the equilibrium water uptake values of FTMs. Two prediction approaches were examined. First, the water sorption was explicitly simulated by iteratively conducting grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Second, the water sorption was predicted based on the chemical potential of the adsorbed water, which was calculated using the Widom insertion or continuous fractional component Monte Carlo (CFCMC) method. The chemical potential-based approach with CFCMC demonstrated good prediction of the equilibrium water uptake values of FTMs with poly(N-vinylformamide-co-vinylamine) as fixed-site carrier and 2-(1-piperazinyl)ethylamine sarcosinate as mobile carrier. The predicted water uptake values increased with increasing mobile carrier content and were in good agreement with the experimental values. Furthermore, the higher water uptake promoted the diffusion of CO 2 , N 2 , and mobile carrier as well as slightly stifled the sorption of N 2 . Such an approach significantly contributes to a more comprehensive theoretical evaluation of FTMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Atomically Fine-Tuning Organic–Inorganic Carbon Molecular Sieve Membranes for Hydrogen Production

Polymeric membranes with great processability are attractive for the H 2 /CO 2 separation required for hydrogen production from renewable biomass with carbon capture for utilization and sequestration. However, it remains elusive to engineer polymer architectures to obtain desired sub-3.3 Å ultramicropores to efficiently sieve H 2 from CO 2 . Herein, we demonstrate a scalable way of carbonizing polybenzimidazole (PBI) at low temperatures, followed by vapor phase infiltration (VPI) to atomically narrow ultramicropores throughout the films, forming hybrid organic–inorganic carbon molecular sieves (CMSs). One VPI cycle (100 s) for the PBI carbonized at 500 °C remarkably increases H 2 /CO 2 selectivity from 9.6 to 83 at 100 °C, surpassing Robeson’s upper bound. The CMS demonstrates a stable H 2 /CO 2 separation performance when challenged with simulated syngas streams and can be fabricated into thin-film composite membranes, outperforming state-of-the-art membranes. Finally, the scalable approach can be ubiquitous to molecularly fine-tune ultramicropores of leading polymeric membranes to further improve their size-sieving ability and thus separation efficiency.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Synthetic membranes and methods of use thereof

The present invention relates to synthetic membranes and use of these synthetic membranes for isolation of volatile organic compounds and purification of water. The synthetic membrane includes a hydrophobic polymer layer located on a polymeric membrane support layer. The invention includes a method of isolating volatile organic compounds with the synthetic membrane by contacting a volatile organic mixture with the hydrophobic polymer layer of the synthetic membrane and removing volatile organic compounds from the polymeric membrane support layer of the synthetic membrane by a process of pervaporation. The invention also includes a method of purifying water with the synthetic membrane by contacting an ionic solution with the hydrophobic polymer layer of the synthetic membrane and removing water from the polymeric membrane support layer of the synthetic membrane by a process of reverse osmosis. The invention also relates to methods of isolating non-polar gases by gas fractionation.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Synthetic membranes and methods of use thereof

Belfort, Georges↗

DOE OSTI2021

Synthetic membranes and methods of use thereof

Belfort, Georges↗

DOE OSTI2022

Mechanically robust PIM-1 and polyphosphazene blended polymer for gas separation membranes

Accordingly, it is an object of this disclosure to provide a blend polymeric membrane to provide the separation of CO2 from a gaseous mixture. The blend polymeric membrane comprises a blend of polyphosphazene and polymers of intrinsic microporosity. Further, the present disclosure also provides a method of use for the blend polymeric membrane for the separation of gases in a gaseous mixture.

Sekizkardes, Ali↗

NASA NTRS1980

Reverse osmosis membrane of high urea rejection properties

Polymeric membranes suitable for use in reverse osmosis water purification because of their high urea and salt rejection properties are prepared by generating a plasma of an unsaturated hydrocarbon monomer and nitrogen gas from an electrical source. A polymeric membrane is formed by depositing a polymer of the unsaturated monomer from the plasma onto a substrate, so that nitrogen from the nitrogen gas is incorporated within the polymer in a chemically combined form.

Johnson, C. C.↗

DOE OSTI2022

Two-Step Thermoresponsive Ultrafiltration Membranes from Polymerization of Lyotropic Liquid Crystals

Here, in this study, we present the fabrication of a two-step thermoresponsive ultrafiltration (UF) membrane through polymerization of a lyotropic liquid crystal (LLC). A mixture of commercially available Pluronic F 127 block copolymer, water (containing ammonium persulfate as the initiator), and polymerizable oil (n-butyl acrylate/ethylene glycol dimethacrylate) is used to create an LLC with a lamellar structure, as characterized by cross-polarized light microscopy and atomic force microscopy. Differential scanning calorimetry is employed to evaluate the thermoresponsive behavior of the polymerized LLC (polyLLC). Two-step thermoresponsiveness (~35 and ~50 °C) of the polyLLC is observed due to the lower critical solution temperature (LCST) of F 127 and melting of the crystalline structure of the polyethylene oxide (PEO) chains of the F 127 surfactant. In the next step, the obtained mesophase is cast on a nonwoven polyester support sheet followed by thermal polymerization. The hydration capacity, water flux, water flux recovery after fouling, and molecular weight cutoff (MWCO) of the obtained membrane are evaluated at different temperatures to examine its thermoresponsiveness. The experimental results reveal that the UF membrane has a reversible thermoresponsive behavior at the LCST and PEO melting of polyLLC. Additionally, the cleaning efficiency of the fouled membrane can be enhanced by using its thermoresponsive behavior, resulting in an extended lifetime of the product. Furthermore, the MWCO of the membrane can be altered with temperature due to the pore size change with temperature stimulus.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Evaluating the impact of functional groups on membrane‐mediated CO 2 / N 2 gas separations using a common polymer backbone

Abstract Polymeric membranes have shown tremendous promise for the separation of CO 2 from flue gas streams. However, few systematic studies have been conducted to better understand the impact that chemical functionalities have on membrane‐based gas separation performance. To address this gap, we herein describe the synthesis and gas separation performance of a series of vinyl‐addition polynorbornenes bearing various CO 2 ‐philic functional groups. To facilitate direct comparison between functional groups, each material was designed to maintain a common polymer backbone. Though the incorporation of CO 2 ‐philic moieties within a dense polymeric membrane is frequently hypothesized to enhance CO 2 solubility, and thereby increase CO 2 /N 2 selectivity, our results demonstrate that the incorporation of CO 2 ‐philic groups onto a common polymer backbone do not necessarily result in increased gas separation performance. Experimental and computational results demonstrate that the incorporation of amidoxime groups onto a polynorbornene backbone increase CO 2 /N 2 selectivity, whereas commonly employed ethereal side chains only increased permeability.

Higgins, Morgan A.↗

DOE OSTI2024

A Pro‐Angiogenic Immunoprotective Membrane for Cell Therapies

Abstract Immunoisolation strategies that rely on porous membranes play an important role in cell transplantation therapies to protect cells from the host's immune system. These membranes must possess immunoprotective properties while facilitating the transport of nutrients and cell products to maintain the functional integrity of encapsulated cells. An easy and scalable process is described to fabricate a dual function porous polymeric membrane that shields cells against immune cell attack and promotes vascularization to address the nutritional and oxygen requirements of transplanted cells. The fabrication process results in a membrane cross‐section with a gradient of nanopores to micropores that support cell immunoisolation and interfacial vascularization requirements, respectively. The membranes demonstrate excellent cell compatibility and effectively prevent T cell transmigration without compromising glucose diffusion and oxygen permeability. In a murine subcutaneous implantation model, membranes are stable for 60 days and exhibit significantly reduced fibrous capsules, with enhanced vascularization near the membrane. These porous polymeric membranes can potentially be used as pro‐angiogenic immunoprotective membranes for cell transplantation applications where maximizing cell viability and function is of critical importance.

Engineering↗

NASA NTRS2002

Development of a New Membrane Casting Apparatus for Studying Macrovoid Defects in Low-G

A new membrane-casting apparatus is developed for studying macrovoid defects in polymeric membranes made by the wet- and dry-casting process in low-gravity. Macrovoids are large (10-50 micron), open cavities interspersed among the smaller pores in the substructure under the gelled skin surface layer of the cast membrane. Although their occurrence is considered endemic to the wet- and dry-casting process since they can lead to compaction or skin rupture in the membrane process, recent studies suggest several useful applications such as transdermal and osmotic drug delivery systems, miniature bioreactors, etc. However, lack of knowledge about the macrovoid formation mechanism is an obstacle to further development of applications using them. An on-going debate is the role of the surface-tension-driven solutocapillary convection during macrovoid formation. The rapid growth of macrovoids within 1-5 seconds and the high polymer concentration in and near macrovoids make it difficult to explain the mechanism of macrovoid growth by diffusion alone, which is the widely accepted hypothesis proposed by Reuvers et al. The hypothesis advanced by our research group can explain this rapid growth via a mechanism that involves diffusion from the casting solution in the meta-stable region to the macrovoid enhanced by solutocapillary convection induced by the steep nonsolvent concentration gradient in the vicinity of the macrovoid. Since macrovoid growth is hypothesized to be the interplay of a solutocapillary-induced driving force counteracted by viscous drag and buoyancy, eliminate the latter provides a means for testing this hypothesis. Moreover, free convection mass transfer in the nonsolvent immersion bath used to cause phase-separation in membrane casting complicates developing a model for both the wet-casting process and macrovoid growth. The low-g environment minimizes gravitationally induced free convection thereby permitting a tractable solution to the ternary diffusion equations that characterize membrane formation. NASA's Parabolic Flight Research Aircraft provides a small window of low-g (approximately 25 s) that can be used to study macrovoid development in both wet- and dry-cast membranes if an appropriate casting apparatus is used. This casting apparatus should be able to cast the membrane in both low- and high-g in a manner so that essential one-dimensional mass transfer conditions are achieved to insure lateral uniformity in the membrane. The apparatus used in previous research on membrane casting in low-gravity was operated with the plunger driven mechanism. The spring-loaded plunger pushes the bottom block containing the polymer casting solution well directly under the absorbent chamber located in the upper stationary block. However, membranes made via this casting apparatus often displayed lateral nonuniformities that precluded obtaining quantitative information on the macrovoid growth process. Thus, it was necessary to determine the reason for these structural irregularities observed in the low-g casting apparatus. Both experimental as well as computer simulation studies of the low-g casting apparatus established that the impulsive action of the plunger caused the undesired structural nonuniformities. The simulation results showed that the width-to-depth aspect ratio of the shallow well that contains the casting solution in this apparatus was not an important factor in minimizing this problem. Even for a 40:1 (width : depth) aspect ratio, any convection induced by the horizontal motion of the interface of the casting solution will be damped out within 6.25x10(exp 4) seconds. However, the experimental studies revealed that the impulsive motion of the plunger caused a 'sloshing' of the casting solution that had to be eliminated. Therefore, the plungerdriven mechanism was changed to a cam-driven mechanism that did not cause any impulsive motion of the casting solution. Other refinements to this new membrane-casting apparatus include provision for removing the membranes from the casting wells in a less destructive manner. This was accomplished by using a slit geometry for the casting well that permitted disassembly for removal of the cast membrane. The materials used in the construction of this casting apparatus were chosen to insure wetting at the side walls and to maintain precise control of the thickness of the polymer solution in the casting well. An additional provision in this new casting apparatus is the ability to carry out both wet- as well as dry-casting. As such, this apparatus permitted the first studies of the wet-casting of polymeric membranes in low-g. Both wet- and dry-casting experiments on NASA's KC-135 research aircraft employing this new membrane-casting apparatus are scheduled in July 2002. The morphology of the resulting membranes will be characterized using an environmental scanning electron microscope (ESEM). The results of these low-g studies will be reported later.

Lee, Hanyong↗

DOE OSTI2023

Protein-activated atomic layer deposition for robust crude-oil-repellent hierarchical nano-armored membranes

Atomic layer deposition (ALD) offers unique capabilities to fabricate atomically engineered porous materials with precise pore tuning and multi-functionalization for diverse applications like advanced membrane separations towards sustainable energy-water systems. However, current ALD technique is inhibited on most non-polar polymeric membranes due to lack of accessible nucleation sites. Here, in this study, we report a facile method to efficiently promote ALD coating on hydrophobic surface of polymeric membranes via novel protein activation/sensitization. As a proof of concept, TiO 2 ALD-coated membranes activated by bovine serum albumin exhibit remarkable superhydrophilicity, ultralow underwater crude oil adhesion, and robust tolerance to rigorous environments including acid, alkali, saline, and ethanol. Most importantly, excellent cyclable crude oil-in-water emulsion separation performance can be achieved. The mechanism for activation/sensitization is rooted in reactivity for a particular set of amino acids. Furthermore, the universality of protein-sensitized ALD is demonstrated using common egg white, promising numerous potential usages in biomedical engineering, environmental remediation, lowcarbon manufacturing, catalysis, and beyond.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Regulating Gas Transport in Molecularly Engineered Polymer Membranes (Final Technical Report)

Energy-efficient separation processes are essential for a wide range of applications ranging from clean fuels (e.g., hydrogen purification) and petroleum refining (e.g., natural gas processing) to water purification and carbon capture. Membrane-mediated separations have shown tremendous promise in providing high productivity and high separation efficiency at significantly lower energy consumption, e.g., up to 90% less energy cost than traditional thermally driven processes such as distillation. Polymeric membranes–the dominant separation membrane materials–have yet to reach their full potential due to their limitations in long-term durability (e.g., productivity loss over the period of their lifetime due to physical aging) or insufficient stability under harsh conditions (e.g., high temperature, chemically complex feeds). This research seeks to establish a new paradigm in polymer membrane material design by harnessing crosslinked model networks with well-defined yet finely tailorable microstructure to facilitate fast and selective gas transport and simultaneously enhance membrane stability. Unlike traditional randomly crosslinked polymers, which suffer from structural inconsistencies and consequently suboptimal gas separation performance, crosslinked model network membranes prepared via a precisely controlled end-linking process enables the creation of previously unattainable microstructure tunability, which, in turn, results in versatile crosslinked membranes with high separation performance that meet the needs of various challenging gas separations. Using model network framework as a fundamental tool by applying this concept in diverse polymer categories, this work has led to the development of various innovative crosslinked membrane structures such as unimodal, bimodal and clustered model networks. These advanced crosslinked polymer membranes not only demonstrate exceptional gas separation performance that significantly outperform existing randomly crosslinked membranes, but also possess excellent long-term durability and robust stability under complex operating conditions. From a fundamental perspective, results from this research provide critical mechanistic insights into gas separation in crosslinked polymer membranes, addressing key knowledge gaps and opening new avenues for membrane design to meet various separation needs. The new membrane materials produced from this research enable the use of polymeric membranes for high temperature gas separations, offering substantial energy and cost savings by eliminating the need for repeated cooling-heating cycles in industrial processes.

02 PETROLEUM↗

DOE OSTI2021

Engineering Li/Na selectivity in 12-Crown-4–functionalized polymer membranes

Significance Lithium is a key ingredient in batteries, which are integral components of next-generation automobiles, airplanes, grid energy storage, and electronic devices. Unfortunately, lithium extraction from natural sources is laborious, slow, and costly, motivating the search for more efficient isolation techniques. While polymeric membranes could reduce the cost of lithium recovery, current membrane materials lack sufficient lithium-ion selectivity. To address this challenge, we introduce a class of polymeric membranes that incorporate ion binding sites, which significantly increases the transport selectivity of LiCl over NaCl. These studies provide guidelines and practical considerations for incorporating specific interactants into polymers that mediate selective ion transport.

36 MATERIALS SCIENCE↗

NASA NTRS1985

The casting of semi-permeable membranes in a microgravity environment

The National Electric Company of Venezuela, C.A.D.A.F.E., is sponsoring the development of this experiment which represents Venezuela's first scientific experiment in space. The experience can be classified as an educational one which could add knowledge to the fundamental study of polymeric membranes. Presently, semi-permeable membranes are being manufactured from several different kind of polymers all over the world and specific applications have been identified in fluid separation processes such as reverse osmosis, ultrafiltration and electrodyalisis. Although, the ultrastructure of asymetric and composite membranes have been under intensive study, still there are many questions about the factors affecting this structure and their degree of correlation. Nevertheless, there is indication that the entire morphological structure of polymeric membranes could be affected by the differences in specific gravity between the cast solution and the coagulation liquid, normally used in the membranes preparation process. The casting of semi-permeable membranes in space might help to identify the effect of gravity upon the structure of these membranes. It is important to recognize that the casting process involves changes of states (liquid-gas, liquid-solid) and that in a micro gravity environment, there will be a reduction on buoyancy-driven natural convection and density gradients

Ivan Vera↗