PREDICTIONS OF COPOLYMER MICELLE BEHAVIOR IN IMMISCIBLE SOLVENTS

We apply the self-consistent field theory of Scheutjens and co-workers1 to describe spherical block copolymer micelles in the presence of two solvents, each selective for one of the blocks. Mean field approximations in layers of spherical shells enable this theory to account for radial variation of concentration. In systems with highly incompatible solvents, the core segment volume fraction profile exhibits a maximum near the core-corona interface while the second solvent segregates in the center of the micelle. In particular, we perform calculations describing our previous experimental studies of poly(ethylene oxide)/polystyrene block copolymers in cyclopentane with trace amounts of water.2-4 We investigate the changes in micelle size and the critical micelle concentration as the background concentration of the second solvent is increased to saturation levels. The size of the core block dominates the micelle capacity to disperse a second solvent. We also propose that the acute sensitivity of micelle structure to the bulk second solvent concentration may be responsible for an unusual increase in micelle size upon dilution when an excess of the second solvent is present.