Mean-field theory of polymer interfaces in the presence of block copolymers

Abstract

A mean-field theory is presented that describes the effects of an A/B diblock copolymer on the properties of an interface between immiscible A and B homopolymers. A complete set of self-consistentfield equations is solved numerically in order to determine the profiles of the different polymeric components and the interfacial tension. These quantities are completely determined by the specification of the homopolymer and copolymer degrees of polymerization, a Flory–Huggins χ parameter describing the thermodynamic interactions between A and B segments, the statistical segment length, and the copolymer chemical potential. At reasonable values of this chemical potential, the interfacial tension vanishes, and the volume fraction of copolymer near the interface is close to 1. The effects of the copolymer on the interfacial properties in this strong segregation regime are governed by the extension of the copolymer blocks away from the interface and are therefore determined primarily by the degree of polymerization of the longer copolymer block. The region of molecular mixing is significantly broadened by the penetration of the copolymer chains into the homopolymer phases. There is a much smaller increase in the width of the region over which A and B segments mix, due to the constraint that the junction between the copolymer blocks must lie within this narrow region. We also find that there is a positive contribution to the interfacial tension, which may give rise to an attractive interaction between segregated polymer layers in high molecular weight polymer matrices. © 1990, American Chemical Society. All rights reserved.