The Interface between 2 Strongly Incompatible Polymers

Abstract

The technique of X-ray reflectometry is used to investigate the interface between two strongly incompatible polymers, polystyrene (PS) and poly(p-bromostyrene) (PBrS). Two thin polymer films are deposited on a glass substrate and various film parameters are determined during annealing. The interfacial width between the polymers is determined with subnanometer resolution. It increases with annealing temperature. A maximum thickness of 1.3 nm is reached at approximately the glass transition temperature T(g) of PBrS where both components become mobile. The increase of the interfacial width with annealing temperature is explained on the basis of mobility and interdiffusion. The Flory-Huggins interaction parameter obtained from the experiment is in good agreement with mean field theoretical approximations. By phase interference microscopy a drastic increase in surface roughness is observed during annealing above T(g) of PBrS. It is explained with respect to a minimization of the interfacial contact area between the components giving rise to a lateral reorganization on a micrometer scale.