Formation of micelles and vesicles in copolymer-homopolymer mixtures

Abstract

A mixture of A-B type diblock copolymer and homopolymer undergoes macro- and micro-phase separations simultaneously at low temperatures. We have carried out computer simulations for this double-phase separation modeled by a coupled set of equations for the local volume fractions. When the strength of incompatibility between B blocks and homopolymers is sufficiently large, copolymer-rich domains form a concentric pattern with a few layers where A-rich and B-rich domains are arrayed alternatively. When the incompatibility is weak, on the other hand, the stripe domains of A and B blocks tend to be perpendicular to the interface dividing the homopolymer-rich and the copolymer-rich domains. The morphological difference is found to affect drastically the kinetics of domain growth. We explore the possibility of vesicle formation such that a bilayer of the copolymer can be formed in the matrix of the homopolymer, which is an interesting feature of the copolymer-homopolymer mixture. We study the statistical properties of a vesicle to calculate the bending and the curvature moduli for the bilayer in the strong segregation limit and in the limit of the negligible membrane width compared to the size of a vesicle.