Adsorption of Copolymer Chains from a Melt onto a Flat Surface

Abstract

We have investigated the segregation of symmetric polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers at interfaces formed between different polymer melts and flat, impenetrable surfaces using elastic recoil detection (ERD). Situations in which the copolymers were allowed to adsorb onto silicon (Si) from PS melts of varying degrees of polymerization, P, were examined. Over the range of concentrations studied, the excess copolymer chains per unit area at the interface, φ*(0), was found to be independent of P, for P > Nc, where Nc is the degree of polymerization of the copolymer chains. At very low concentrations, φ*(0) exhibited a strong linear dependence on φc, the equilibrium volume fraction of chains in the bulk of the homopolymer. For φc ≥ 0.012 (φ*(0) ≈ 42 Å), φ*(0) became virtually independent of φC. This value of φ*(0) corresponded to the interface excess at which the Si surface became saturated with PMMA segments. The energy of interaction between a copolymer chain and the surface was determined to be of order kBT. Interfacial segregation of the copolymers was not observed when the homopolymer host was PMMA, poly(vinyl chloride), or a blend of PS and poly(phenylene oxide). No segregation of the copolymers was observed at PS/gold interfaces. On the other hand, segregation of the PS-PMMA copolymers at PS/A1 interfaces was very strong. © 1992, American Chemical Society. All rights reserved.