Block Polymer Nanostructures in Ionic Liquids: New Opportunities in Science and Engineering
Block polymers provide a remarkably versatile platform for achieving desired nanostructures by self-assembly, with lengthscales varying from a few nanometers up to serveral hundred nanometers. Ionic liquids are an emerging class of solvents with an appealing set of physical attributes. These include negligible vapor pressure, high chemical and thermal stability, tunable solvation properties, high conductivity, and wide electrochemical windows. For various applications it will be necessary to solidify the ionic liquid into particular spatial arrangements, such as membranes or gels, or to partition the ionic liquid in coexisting phases, such as microemulsions and micelles. We have embarked on a systematic exploration of ways to achieve this by block copolymer self-assembly. In so doing, a number of fascinating physical phenomena have emerged, which will be highlighted in this talk. Examples include the "micelle shuttle", a phenomenon whereby intact micelles transfer reversibly an aqueous phase into an ionic liquid, as a function of temperature, and doubly responsive micelles, which undergo demicellization and inverse micellization upon heating. Thermoreversible gelation of triblock copolymers provides a simple route to "ion gels" with tunable modulus and ionic conductivity. Applications of these gels in plastic electronics and gas separations will also be described.