Equilibrium emulsification of polymer blends by diblock copolymers

Abstract

The onset and morphology of various equilibrium emulsion phases for an A and B homopolymer mixture with diblock A-B copolymers as the compatibilizer, is investigated. Attention is focused on the relation between the relative lengths of the blocks and the elastic properties of the interfacial layer which determines the phase behavior. The curvature elastic moduli K and K, as well as the spontaneous radius of curvature, R 0, are obtained. The situation studied here differs from the conventional interfacial approach to microemulsions with short-chain surfactants, in that (1) the area per copolymer Σ on the interface is not fixed, but is determined by a balance between the elastic energy of the chain and the interfacial tension ; thus Σ also depends on the curvatures ; (2) as a result of (1), the elastic coefficients K, K and R0 are interdependent, and in contrast to the short chain systems, the saddle-splay modulus K is always negative (see text for the sign convention). The phase diagram as a function of these parameters is therefore different from that obtained by conventional interfacial descriptions for short surfactants