Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K18: Polymeric Membranes - Water PurificationFocus
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Sponsoring Units: DPOLY Chair: Rafael Verduzco, Rice University Room: 277 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K18.00001: Charge Mosaic Membranes Fabricated from Chemically Tailored Copolymer Materials William Phillip, Siyi Qu, Sherwood Benavides, Aaron Hunter, Yi Shi, Haifeng Gao The majority of state-of-the-art membranes implemented in water treatment processes utilize a size-selective, steric exclusion mechanism to sort dissolved solutes from solution. Catalyzed by recent advances that provide nanoscale control over material architectures, next generation membranes are pushing the limits of size-selective separations. As such, there is a growing interest in chemically-selective membranes that allow for efficient separations based on chemical factors. In this work, we discuss the use of a copolymer-derived membrane platform, which can be post-synthetically modified, in the production of chemically-selective charge mosaic membranes. These mosaic membranes possess distinct, counter-charged domains that cover the membrane surface and traverse the membrane thickness. This unique nanostructure allows dissolved salts to permeate through the mosaic more rapidly than water, even though water is three times smaller in size. A series of pressure-driven solute rejection experiments conducted over a range of ionic strengths demonstrate this distinct transport property and offer insights into the fundamental mechanisms governing the performance of these novel membranes. Through this example, we demonstrate that membranes that are based on nanostructured copolymer materials provide a scalable and efficient platform that can be tailored to myriad chemically-selective separations in future applications. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K18.00002: Constructing ion conducting, nanostructured block copolymer electrolytes through block copolymer self-assembly and block copolymer lithography Christopher Arges, Yu Kambe, Moshe Dolejsi, Guangpeng Wu, Paul Nealey The tools of directed self-assembly and block copolymer lithography realized a series of nanostructured anion and cation conducting polymer electrolyte films with different molecular architectures (e.g., ionic domain connectivity and tortuosity). Key results emphasize that ionic domains with poor alignment and terminal defects have a catastrophic effect on ionic conductivity - a key transport property in ion-exchange membranes for electrochemical applications. Conversely, ensuring complete ionic domain connectivity (i.e., elimination of terminal defect sites at the molecular level) and a tortuosity of one substantially improved ionic conductivity values (almost 100x fold). Controlling the architecture of aggregated ionic domains at the molecular level played a prominent role in the bulk ionic conductivity properties of polymer electrolyte materials. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K18.00003: Controlling the Pore Size of Mesoporous Carbon Thin Films through Thermal and Solvent Annealing. Zhengping Zhou, Guoliang Liu Herein we describe a method for controlling the pore size of mesoporous carbon thin films from poly(acrylonitrile-block-methyl methacrylate) (PAN-b-PMMA) synthesized via RAFT polymerization. We systematically investigated the self-assembly behavior of PAN-b-PMMA thin films during thermal and solvent annealing, as well as the pore size of mesoporous carbon thin films after pyrolysis. The as-spin-coated PAN-b-PMMA microphase-separated into globular nanostructures, and the globular nanostructures evolved into various morphologies after thermal or solvent annealing. Surprisingly, through thermal annealing and subsequent pyrolysis of PAN-b-PMMA into mesoporous carbon thin films, the pore size and the center-to-center spacing of pores increased significantly with annealing temperature, different from most block copolymers. In addition, the choice of solvent during solvent annealing strongly influenced the block copolymer nanostructures and the pore size of mesoporous carbon thin films. The discoveries herein provide a simple strategy to control the pore size of mesoporous carbon thin films by tuning thermal or solvent annealing conditions, instead of synthesizing a series of block copolymers of various molecular weights and compositions. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 9:12AM |
K18.00004: Nanostructured membranes based on polysulfone homopolymers and copolymers. Invited Speaker: Suzana Nunes Polyethersulfone is one of the most successful polymers for membranes with applications varying from seawater desalination to hemodialysis. Their manufacture however is traditionally done by solution casting and phase inversion using solvents, which are now considered negative for the environment. We have been working on the membrane manufacture using ionic liquids as green solvent alternative. Polyethersulfone, and polyetherimide sulfone membranes, as flat-sheet and hollow fibers, were prepared from solutions in different ionic liquids (D. Kim et al. Green Chemistry 2016). Thermodynamic and rheological investigation were conducted to optimize the membrane morphology, leading to permeances of 20-65 Lm-2h-1bar-1 useful for instance for separations of peptides with molecular weight in the range of 800 to 3500 gmol-1. We also synthesized block copolymers with polysulfone segments and explored them for membrane preparation with low fouling, high porosity and narrow pore size distribution (Y. Xie et al. Polymer Chemistry). The self-assembly of the copolymer in solution, leading to the membrane formation was investigated by cryo electron microscopy, supported by modeling (dissipative particle dynamics).\\ \\In collaboration with: Dooli Kim, Yihui xie, Burhannudin Sutisna, King Abdullah University of Science and Technology [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K18.00005: Nanostructured Block Polymer Membranes as High Capacity Adsorbers for the Capture of Metal Ions from Water Bryan Boudouris, Jacob Weidman, Ryan Mulvenna, William Phillip The efficient removal of metal ions from aqueous streams is of significant import in applications ranging from industrial waste treatment to the purification of drinking water. An emerging paradigm associated with this separation is one that utilizes membrane adsorbers as a means by which to bind metal salt contaminants. Here, we demonstrate that the casting of an A-B-C triblock polymer using the self-assembly and non-solvent induced phase separation (SNIPS) methodology results in a nanoporous membrane geometry. The nature of the triblock polymer affords an extremely high density of binding sites within the membrane. As such, we demonstrate that the membranes with binding capacities equal to that of state-of-the-art packed bed columns. Moreover, because the affinity of the C moiety can be tuned, highly selective binding events can occur based solely on the chemistry of the block polymer and the metal ions in solution (i.e., in a manner that is independent of the size of the metal ions). Due to these combined facts, these membranes efficiently remove heavy metal (e.g., lead- and cadmium-based) salts from contaminated water streams with greater than 95{\%} efficiency. Finally, we show that the membranes can be regenerated through a simple treatment in order to provide long-lasting adsorber systems as well. Thus, it is anticipated that these nanostructured triblock polymer membranes are a platform by which to obtain next-generation water purification processes. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K18.00006: Multiscale Simulations of PS-PEO Block Copolymers with LiPF$_{6}$ Ions in Lamellar Phase: Equilibrium Characteristics Vaidyanathan Sethuraman, Santosh Mogurampally, Venkat Ganesan Multiscale simulations involving coarse-graining and inverse coarse-graining steps, are performed to characterize the structural equilibrium properties of polystyrene-polyethylene oxide (PS-PEO) block copolymer (BCP) melt in the ordered lamellar phase doped with Li-PF$_{6}$ salt. We compared the structural distribution functions between various entities in the system with that of PEO homopolymer melts. Anion-cation and cation-oxygen radial distribution functions show significantly stronger coordination in block copolymer melts when compared to the homopolymer melts. RDFs computed in PEO and PS domains separately show that the increased binding of the ion pairs in the BCP melts arise from the strong binding in the PS domains. Further, local structural distributions of cation-anion pairs reveal that the binding is stronger near the interface of the PS-PEO compared to that in the bulk of the PEO domain. The preceding quantities are also studied as a function of salt loading. An important result from such studies is that the number of free ions is found to decrease with increasing salt concentration in both block copolymer and homopolymer melts. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K18.00007: Membranes with charged nanopores from the assembly of random copolymer micelles Ayse Asatekin In this study, we aimed to prepare synthetic polymer membranes that can separate small molecule solutes based on charge by mimicking biological pores like ion channels: Pores 1-5 nm in diameter, lined with functional groups that interact with the target. We found that random copolymers that combine highly hydrophobic fluorinated repeat units of trifluoroethyl methacrylate with ionizable repeat units of methacrylic acid form micelles and vesicles in methanol. When these micelles are coated onto the surface of a porous support membrane whose pores are smaller than the micelles and then immersed into water, a selective layer of micelles packed together is formed. The gaps between the micelles act as carboxylate-functional nanochannels. The membrane showed charge-based selectivity between organic molecules, rejecting anionic solutes while passing neutral ones. The carboxyl groups can be post-functionalized to alter the selectivity of the membrane for desired separations. This shows the potential of using polymer self-assembly and functionality to design membranes that mimic biological pores while maintaining scalable manufacturing methods. We believe these approaches will eventually lead to novel membranes that can separate molecules of similar size but different chemical structure. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K18.00008: Nanofiltration Membranes for Water Purification: structure-transport relationships and applications Steven Jons, Mou Paul, Tamlin Matthews, Leaelaf Hailemariam Nanofiltration (NF) membranes are used for separating salts and small neutral molecules. NF membranes show unique selectivity properties compared to reverse osmosis membranes as it can selectively pass monovalent salts and neutral molecules as a function of charge and molecular weight cut-off which are dependent on membrane characteristics and operating conditions. Dow Water {\&} Process solutions has been a pioneer in the membrane based water purification field and Dow's role was instrumental in developing several NF membranes for different applications. However, the characterization of NF membranes and hence the development of structure-property relationship is challenging due to the nanoscale thin, crosslinked nature of the membrane. Recently significant efforts were employed to develop analytical capabilities to understand polymer structure and composition and it had been possible to achieve a structure-property relationship for NF membranes. This paper will highlight similar relationships and will also focus on the relationships of membrane structure with membrane transport properties and how this relationship influences products for different application areas such as in oil field, sweetener and minimum liquid discharge etc. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K18.00009: 3D morphological characterization of the polyamide active layer of RO and NF membranes using TEM and soft X-ray scattering Tyler Culp, Mou Paul, Abhishek Roy, Steve Rosenberg, Michael Behr, Manish Kumar, Enrique Gomez Polyamide-based thin-film composite (TFC) membranes used for reverse osmosis (RO) and nanofiltration (NF) separation processes are at the forefront of water desalination and purification technologies due to their high salt rejection, high energy efficiency, and ease of operation. Nevertheless, in spite of the benefits of RO and NF membranes, many open questions about the internal nanostructure of the membrane active layer remain, such as the dispersion and distribution of acid functional groups. We demonstrate that resonant soft X-ray scattering (RSOXS), where the X-ray energy is tuned to absorption edges of the constituent materials, is a powerful tool to examine the microstructure of the polyamide layer. In conjunction with complementary techniques such as transmission electron microscopy (TEM), where tomography is used to obtain a 3D reconstruction of the polyamide active layer, the effect of cross-linking can be quantified in 3D for a systematic series of membranes. This relationship can then be applied to a series of commercially available RO and NF membranes where the effect of polyamide cross-linking on their respective structure and water transport properties can be evaluated. The combination of RSOXS with traditional characterization tools provides a strategy for linking the chemical structure to the morphology and water transport properties of RO and NF membranes. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K18.00010: Atom Resolved Electron Microscpe Images of Polyvinylidene Fluoride Nanofibers for Water Desalination Suqi Liu, Darrell Reneker Ultra-thin nanofibers of polyvinylidene fluoride (PVDF), observed with an aberration corrected transmission electron microscope, in a through focus series of 50 images, revealed three-dimensional positions and motions of some molecular segments. The x,y positions of fluorine atoms in the PVDF segments were observed at high resolution as described in (DOI: 10.1039/c5nr01619c). The methods described in (DOI:10.1038/nature11074) were used to measure the positions of fluorine atoms along the observation direction of the microscope. PVDF is widely used to separate salt ions from water in reverse osmosis systems. The observed separation depends on the atomic scale positions and motions of segments of the PVDF molecules. Conformational changes and the associated changes in the directions of the dipole moments of PVDF segments distinguish the diffusion of dipolar water molecules from diffusion of salt ions to accomplish desalination. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K18.00011: Investigations into the microstructure and performance of ion-modified polysulfone membranes Matthew Green, John Felmly Access to clean water is one of the grand challenges facing society today and in the future. Membrane-based water purification techniques are the current state of the art, but face limitations including thermodynamically unfavorable transport, high material and operation costs, the perm-selectivity tradeoff, and an insufficient number of materials capable of selectively removing fertilizer and pesticide compounds. Polysulfones have been implemented in a variety of membrane-based technologies for water purification and desalination. Introducing charged moieties into the polymer repeat unit introduces added functionality, develops new morphological features, improves thermomechanical performance, and enables tailored a selectivity toward small molecules or salts. This work reviews recent developments in the preparation of polysulfones that can undergo post-polymerization modification reactions to introduce pendant cations, anions, or zwitterions. The synthesis and subsequent characterization will be discussed briefly. Then, the processing of the polymers into thin film and hollow fiber membranes will be discussed as well as their performance for desalinating solutions with varying saline concentrations and solutions containing common fertilizer and pesticide compounds. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K18.00012: Strong adsorption of random heteropolymers on protein surfaces Trung Nguyen, Baofu Qiao, Brian Panganiban, Christopher Delre, Ting Xu, Monica Olvera de la Cruz Rational design of copolymers for stablizing proteins' functionalities in unfavorable solvents and delivering nanoparticles through organic membranes demands a thorough understanding of how the proteins and colloids are encapsulated by a given type of copolymers. Random heteropolymers (RHPs), a special family of copolymers with random segment order, have long been recognized as a promising coating materials due to their biomimetic behaviors while allowing for much flexibility in the synthesis procedure. Of practical importance is the ability to predict the conditions under which a given family of random heteropolymers would provide optimal encapsulation​. Here we investigate the key factors that govern the adsorption of RHPs on the surface of a model protein. Using coarse-grained molecular simulation we identify the conditions under which the model protein is fully covered by the polymers. We have examined the nanometer-level details of the adsorbed polymer chains and found a clear connection between the surface coverage and adsorption strength, solvent selectivity and the volume fraction of adsorbing monomers. The results in this work set the stage for further investigation on engineering biomimetic RHPs for stabilizing and delivering functional proteins across multiple media. [Preview Abstract] |
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