The goal of this project is to advance a new class of functional nanostructured materials by combining ionic liquids with block copolymers. Ionic liquids exhibit many appealing properties, including chemical and thermal stability, vanishing vapor pressure, tunable solvation, high ionic conductivity, and high dielectric constant, that render them appealing as potential 'green' solvents, and as key ingredients in plastic electronics, batteries, fuel cells, gas separation membranes, and actuators. To realize these properties in advanced materials applications, it is necessary to solidify the material, and/or to confine the ionic liquid within a desired nanostructure. Block copolymers offer unprecedented flexibility to direct self-assembly over lengthscales from 1-100 nanometers, while simultaneously providing mechanical integrity. Three different sub-projects are envisioned that address fundamental issues in polymer materials science, and each exploits a unique aspect of nanostructured copolymer/ionic liquid mixtures. First, a quantitative understanding of the rate of chain exchange in block copolymer micelles will be established, by utilizing time-resolved small-angle neutron scattering on isotopically labeled micelle mixtures. By virtue of the wide usable temperature range of ionic liquids, and the ease with which critical micellization temperatures can be tuned predictably by blending homologous imidazolium cations, the crossover from 'ergodicity' to 'non-ergodicity' will be delineated systematically. Second, the recent discovery of ionic-liquid-filled vesicles dispersed in water will be extended to nanoreactor applications, whereby the catalyst is confined to the vesicle interior, and may be recovered easily. The aqueous matrix mitigates the severe cost and mass transfer restrictions of ionic liquid reaction media, while the vesicle membrane will regulate the rate of reactant and product partitioning between aqueous and ionic liquid phases. Last, an ABC triblock terpolymer approach is proposed to prepare crosslinked bi- and tri-continuous membranes with conductive, ionic-liquid-rich nanochannels, with the goal of accessing unprecedented combinations of high mechanical toughness and ionic conductivity.
NON-TECHNICAL SUMMARY: Composite materials prepared from polymers and room temperature ionic liquids are under active consideration for many advanced technologies, including biomass modification, gas separation membranes, plastic electronics, ion batteries, and fuel cells. Success in any of these areas would have profound societal impact in terms of energy conservation, sustainable plastics, and portable energy storage. Simultaneous optimization of diverse properties, such as high ionic transport, mechanical integrity, and facile processing, can best be achieved through structural control at the nanometer scale. Thus, the combination of structure-directing block copolymers and functional ionic liquids will accelerate the development of advanced materials. Graduate students will acquire a broad suite of skills in polymer synthesis and characterization, light, x-ray and neutron scattering, fluorescence spectroscopy, and electron microscopy. They will also have extensive opportunities to present technical talks and posters to external audiences, as well as to mentor talented undergraduates in research. High school students from the greater Twin Cities, particularly women and underrepresented minorities, will be exposed to polymer science through "Polymer Day: You Make It, You Break It", a hands-on component of a broader "Exploring Careers in Science & Engineering" summer camp.
