(797b) Thermodynamics of Block Copolymer Micellization in Ionic Liquid Solvents

Hoarfrost, M. L., University of California, Berkeley
Lodge, T. P., University of Minnesota

Block copolymers can be designed to self-assemble in solution into micelles with complex shapes and functionality, which are useful for a variety of applications in many industries.  However, our understanding of the thermodynamics of block copolymer micellization has been limited by the long experimental time scales for micelle equilibration, which stem from the large energy barrier for extracting long solvophobic copolymer segments from micelle cores into solution.  This limitation is exacerbated by the limited temperature ranges of water and volatile organic solvents traditionally used in micelle solutions.  In this work, we study the phase behavior of block copolymer micelles in ionic liquid solvents.  The negligible volatility of ionic liquids allows for thermal annealing and provides an opportunity to study micelle phase behavior over a much larger temperature window than previously possible.  Furthermore, the solvent quality can be precisely tuned by mixing ionic liquids.  We first characterize the solvent quality of ionic liquid mixtures for the solvophobic component of a block copolymer using light and neutron scattering.  We then show how micelle phase boundaries (i.e. critical micelle temperature and concentration) depend on solvent quality and block copolymer degree of polymerization.