Professor
Contact
389 Amundson Hall
421 Washington Avenue SE
Minneapolis, MN 55455
Professor
Through the close interplay of scalable chemical synthesis and physical materials characterization, our research group seeks to manipulate the self-assembly of organic molecules into materials with well-defined nanoscale morphologies that manifest unusual and useful bulk properties. Each project area emphasizes the “bottom up” molecular construction of materials with the ultimate goal of uncovering new guiding principles for their design. Specific research project focus on the development of new economical and sustainable materials for energy storage and use, membranes for efficient chemical separations, and materials for applications ranging from advanced nanolithography to enhanced oil recovery.
Lyotropic Liquid Crystal Self-Assembly: Towards Next-Generation Ion Exchange Membranes. Polymer electrolyte membranes (PEMs) that shuttle H+ or OH- are essential components of fuel cells and solar fuel production schemes. While various limitations of known PEMs have spurred the development of new materials, reliable molecular design criteria that guide syntheses of superior ion transporting media remain obscure. To address this fundamental yet technologically important challenge, we have developed a new small molecule surfactant platform that exhibits an unusual tendency to self-assemble in water into bicontinuous liquid crystalline phases comprised of interpenetrating aqueous and hydrophobic domains, which percolate over macroscopic lengthscales with tunable nanopore diameters (~0.6-6 nm) and well-defined pore functionalities. Using these self-assembling systems, we have produced a model set of nanoporous membrane materials that we are studying for fuel cell, water desalination, and selective chemical separations applications. We are also using these materials as an experimental platform to probe fundamental mechanisms of H+ and OH- transport in water-filled nanoporous media and to elucidate the structure of water in soft, ionic nanoconfinement using neutron scattering techniques.
Polymers for Advanced Li-ion Batteries: Advanced Li-ion batteries for advanced transportation applications suffer from several important drawbacks, some of which stem from the poor oxidative and reductive stabilities of typical battery electrolytes. To address this important issue, we have recently developed a new class of polymeric lithium-single ion conducting electrolytes that exhibit unusual electrochemical stabilities. We are probing structure property relationships within this new class of materials in order to assess their viability as next generation electrolytes for high power Li-ion batteries.
Segmental Dispersity Effects in Block Copolymer Self-Assembly: Modern polymerization techniques enable syntheses of functional block copolymers with unusual thermal, electronic, and ionic conductivities. However, these new macromolecular syntheses often introduce significant molecular weight polydispersity (a chain length heterogeneity) into one or more of the copolymer blocks. Conventional wisdom suggests that chain length uniformity (“monodispersity”) is a prerequisite for periodic nanoscale self-assembly of block copolymers. Few studies have questioned the validity and stringency of this preconceived notion. We are studying the melt-phase behavior of ABA-type triblock copolymers comprising either polydisperse A or B blocks. Contrary to conventional wisdom, polydisperse ABA BCPs also assemble into a rich array of periodic nanoscale structures with unexpectedly enhanced thermodynamic stabilities as compared to their monodisperse analogs. Based on these insights, we are now studying Li-ion transport through disperse block copolymers for potential applications in advanced batteries.
Self-Assembly of Non-Linear Block Polymer Architectures: Block polymers self-assemble into a variety of nanostructured morphologies, as a consequence of the molecular frustration induced by coupling two or more immiscible polymer segments into a single macromolecule. One potential block polymer application relies on their periodic microdomains as templates for advanced microelectronics and mesoporous inorganic materials with extremely small feature sizes. We exploring the fundamental physical of the self-assembly of non-linear block polymer architectures, toward the development of templates for sub–10 nm patterning applications.