Correlating Transport with Ionomer Membrane Structure from Molecular to Micron Scales

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

NON-TECHNICAL: Ionic polymer membranes are used to purify water, convert chemical energy to electrical energy (batteries and fuel cells), and conduct a wide variety of chemical separations. By controlling membrane chemical structure, it is possible to generate desirable highly conductive (but soft and liquid-like) regions that are surrounded and supported by mechanically and chemically robust regions. A key problem in designing new membranes lies in understanding the details of these various regions in the membranes, and how these regions affect the movement (transport) of water and ions such as lithium, sodium, and chloride. This project pulls together disparate techniques and theories, including nuclear magnetic resonance (NMR), computational simulations, electron microscopy, and X-ray analysis, to understand how membrane structure influences properties. Indeed, new insights into membrane behaviors can only arise from such a combined multi-disciplinary approach. Such new fundamental knowledge would enable the design of membrane structures to accelerate ion and water motions. In turn, these advances in design would provide valuable information to engineers and entrepreneurs to increase the efficiency and decrease the cost of devices such as water purification systems and advanced power sources. Since membrane technology represents a $15B (and growing) commercial market, such advances could bring huge gains in US productivity and competitiveness. The project also involves education and training of undergraduate and graduate students, as well as K-12 educational outreach. TECHNICAL: Membrane-separations applications such as reverse-osmosis water desalinization and fuel cells involve the selective transport of water, alcohols, and ions through an ion-containing polymer (an ionomer). What effects drive the transport of these various mobile species inside an ionomer membrane? These effects can be thought to arise from a combination of two major contributions: 1) local intermolecular interactions such as ion and water associations, polymer chain topology, or acidity; 2) morphological features such as phase symmetry (cylindrical, lamellar, cubic) and domain sizes and properties. This project will work toward an experimental and theoretical framework for quantitatively separating and fundamentally understanding these two major regimes that affect transport. By combining an array of cutting-edge nuclear magnetic resonance (NMR) methods combined with molecular dynamics simulations, microscopy and X-ray analyses, this project will systematically study water and ion diffusion as well as local intermolecular associations inside ionomer membranes and thus build a more comprehensive mechanistic understanding of permeation and selectivity in these materials. Starting with existing theories of molecular transport, fluid permeation through porous media, electrolytic transport, and oriented soft matter, new thinking and theories will arise regarding membrane behaviors. In a broader context, this project aims toward design of all new materials that are less expensive, more efficient in energy use, more robust, and more specific to desired tasks. Students and collaborators involved in this project will gain sophisticated and fundamental knowledge of polymer membrane behaviors. This new knowledge will be integrated into undergraduate and graduate polymer science classes on the Virginia Tech campus, and propagated to children and their parents in a K-12 educational outreach program in the New River Valley region of Southwest Virginia.