Through the close interplay of organic materials synthesis and physical materials characterization, my research group uses chemical synthesis as a tool to manipulate the self-assembly of organic molecules into materials with well-defined supramolecular structures with unusual and useful bulk properties. Each project area emphasizes this molecular approach in addressing significant challenges in the development of materials for energy storage and utilization and for sustainability, while uncovering physicochemical principles that will guide the design of new functional organic materials. Research in my group leverages our combined skills in synthetic and physical chemistry to address three significant challenges in materials chemistry:
Polydispersity Effects in Block Copolymer (BCP) Self-assembly. Modern polymerization techniques enable the incorporation of functional monomers into block copolymers to yield new materials with unusual thermal, electronic, and ionic conductivities. However, these new BCP syntheses often introduce significant molecular weight polydispersity or chain length heterogeneity into one or more of the copolymer blocks. Conventional wisdom stipulates that chain length uniformity (“monodispersity”) is a prerequisite for useful periodic nanoscale BCP self-assembly. Few studies have questioned the validity and stringency of this preconceived notion. To exploit the full potential of these materials, we are studying the melt-phase behavior of ABA-type triblock copolymers containing a polydisperse center (B) block flanked by monodisperse end (A) 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 synthesizing and characterizing a series of new Li-ion conducting block copolymers for high energy density, high power batteries for transportation applications.
Lyotropic Liquid Crystal-based 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. In the near future, we plan to use these materials as an experimental platform to probe fundamental mechanisms of H+OH- transport in water-filled nanoporous media and to elucidate the structure of water in soft, ionic nanoconfinement using neutron scattering techniques.
Polymeric Materials for Advanced Li-ion Batteries. Advanced Li-ion batteries for 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 oxidative and reductive 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.