Microphase Separation in a Mixture of Block Copolymers in the Strong Segregation Regime

Microphase separation in a blend of A−B and C−B block copolymers with strong A−B and C−B incompability is considered in the strong segregation regime. It is assumed that the length of the B block is always much larger than the lengths of A and C blocks, so the complex spherical micelles containing shorter A and longer C chains are formed. The inner structure of the complex A−C micelle is considered, and the distribution of volume fractions of A and C monomer units is calculated. It is shown that shorter A chains are distributed mainly in the periphery of the micelle, while C chains are coiled in the center of this micelle. Macroscopic separation in this blend is studied. It is shown that, in the mixtures with a small fraction of C−B block copolymer, a two-phase structure should be observed: one phase consists of practically pure A micelles, while the other phase the complex A−C micelles, with enriched contents of longer C chains, are formed. For chemically different A and C blocks, even slight A−C repulsion leads to phase separation between the phases with pure A and pure C micelles.