Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P4: Physics of Polymer Membranes for Water Purification |
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Sponsoring Units: DPOLY Chair: Alamgir Karim, National Institute of Standards and Technology Room: 306/307 |
Wednesday, March 18, 2009 8:00AM - 8:36AM |
P4.00001: Transport of water and solutes in reverse osmosis and nanofiltration membranes Invited Speaker: The polyamide active layers of reverse osmosis and nanofiltration membranes used for water purification are real-world examples of nanoscale functional materials: the active layer is only $\sim $100 nm thick. Because the active layer is formed by a process of interfacial polymerization, the structure and composition of the membrane is highly inhomogeneous and even such basic physical and chemical properties as the atomic density, swelling in water, the distribution of charged species between water and membrane, and the mobility of water and ions, are poorly understood. We are using Rutherford backscattering spectrometry (RBS) to determine the composition, roughness, and thickness of the membrane; reveal the surprisingly high solubility of salt ions in the polymer active layer; analyze the acid-base chemistry of charged functional groups; and determine the degree of polymer cross-linking. Measurements of mass-uptake and adsorption-induced mechanical stress of membranes in humid air enable us to determine the water solubility, specific volume of water, and the mechanical strength of the membrane. Comparisons between these equilibrium data and the permeability of the membrane to water and salts show that the mobility of water molecules in the membrane approaches the mobility of bulk water, and that the rejection of salt ions is accomplished by low mobility, not low solubility. My collaborators in this work are Xijing Zhang, Orlando Coronell, and Prof. Benito Mari\~{n}as. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 9:12AM |
P4.00002: High Flux Nanofibrous Membranes for Water Purification Invited Speaker: Recently, nanofibrous materials have been made more readily available in large part due to advances in electro-spinning and related technologies, including the use of a combination of electrostatic and gas-blowing forces. The non-woven structure has unique features, including interconnected pores, very large surface-to-volume ratio, and ease of surface modifications which enable such scaffolds to have many biomedical and industrial applications. The chemical composition of electrospun membranes can be adjusted by using different polymers, polymer blends or nanocomposites, made of organic or inorganic materials. In this talk, we demonstrate a breakthrough technology on thin-film nanocomposite membranes for high-flux water purification based on nanofiber scaffolds. The breakthrough incorporates two new and unique concepts of the membrane design: (1) the replacement of the conventional flux-limited porous substrate with a highly porous nanofibrous scaffold, and (2) the creation of a very thin, strong and functional nanocomposite barrier layer, imbedded with interconnected and directed water channels. Preliminary experiments on the hierarchical design and assembly of this unique nanofibrous membrane have already revealed very promising potentials. By using a hydrophilic nanocomposite barrier layer, an asymmetric electrospun nanofibrous mid-layer scaffold and a non-woven microfibrous support, the flux rate of this not yet optimized membrane system is 3-10 times better than that of the best among all known conventional ultrafiltration/nanofiltration media without losing the high rejection and low fouling criteria. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:48AM |
P4.00003: Polymers for Waste Water Treatment Invited Speaker: |
Wednesday, March 18, 2009 9:48AM - 10:24AM |
P4.00004: Carbon Nanotube Membranes for Water Purification Invited Speaker: Carbon nanotubes are an excellent platform for the fundamental studies of transport through channels commensurate with molecular size. Water transport through carbon nanotubes is also believed to be similar to transport in biological channels such as aquaporins. I will discuss the transport of gas, water and ions through microfabricated membranes with sub-2 nanometer aligned carbon nanotubes as ideal atomically-smooth pores. The measured gas flow through carbon nanotubes exceeded predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeded values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations and measured for aquaporins. More recent reverse osmosis experiments reveal ion rejection by our membranes. Based on our experimental findings, the current understanding of the fundamentals of water and gas transport and of ion rejection will be discussed. The potential application space that exploits these unique nanofluidic phenomena will be explored. The extremely high permeabilities of these membranes, combined with their small pore size will enable energy efficient filtration and eventually decrease the cost of water purification.\\[4pt] In collaboration with Francesco Fornasiero, Biosciences and Biotechnology Division, PLS, LLNL, Livermore, CA 94550; Sangil Kim, NSF Center for Biophotonics Science \& Technology, University of California at Davis, Sacramento CA 95817; Jung Bin In, Mechanical Engineering Department, UC Berkeley, Berkeley CA 94720; Hyung Gyu Park, Jason K Holt, and Michael Stadermann, Biosciences and Biotechnology Division, PLS, LLNL; Costas P. Grigoropoulos, Mechanical Engineering Department, UC Berkeley; Aleksandr Noy, Biosciences and Biotechnology Division, PLS, LLNL and School of Natural Sciences, University of California at Merced. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 11:00AM |
P4.00005: Hierarchical Fiber Structures Made by Electrospinning Polymers Invited Speaker: A filter for water purification that is very thin, with small interstices and high surface area per unit mass, can be made with nanofibers. The mechanical strength of a very thin sheet of nanofibers is not great enough to withstand the pressure drop of the fluid flowing through. If the sheet of nanofibers is made thicker, the strength will increase, but the flow will be reduced to an impractical level. An optimized filter can be made with nanometer scale structures supported on micron scale structures, which are in turn supported on millimeter scale structures. This leads to a durable hierarchical structure to optimize the filtration efficiency with a minimum amount of material. Buckling coils,\footnote{Tao Han, Darrell H Reneker, Alexander L. Yarin, Polymer, Volume 48, issue 20 (September 21, 2007), p. 6064-6076.} electrical bending coils\footnote{Darrell H. Reneker and Alexander L. Yarin, Polymer, Volume 49, Issue 10 (2008) Pages 2387-2425, DOI:10.1016/j.polymer.2008.02.002. Feature Article.} and pendulum coils\footnote{T. Han, D.H. Reneker, A.L. Yarin, Polymer, Volume 49, (2008) Pages 2160-2169, doi:10.1016/jpolymer.2008.01.0487878.} spanning dimensions from a few microns to a few centimeters can be collected from a single jet by controlling the position and motion of a collector. Attractive routes to the design and construction of hierarchical structures for filtration are based on nanofibers supported on small coils that are in turn supported on larger coils, which are supported on even larger overlapping coils. ``Such top-down'' hierarchical structures are easy to make by electrospinning. In one example, a thin hierarchical structure was made, with a high surface area and small interstices, having an open area of over 50\%, with the thinnest fibers supported at least every 15 microns. [Preview Abstract] |
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