Surface segregation amplification in miscible polymer blends near criticality

Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, The University of Pennsylvania - Philadelphia, PA 19104-6272, USA

Received: 17 September 1996
Accepted: 13 March 1997

Abstract

In atomic, small molecule or polymeric multicomponent materials, surface compositions naturally differ from the bulk because one component (or phase) will generally favor the surface region. Binary polymer blends represent a model system to investigate surface enrichment because segregation is enhanced by the small combinatorial entropy of mixing and amplified by chain connectivity (relative to small-molecule systems). Therefore, polymers are advantageous systems for probing the thermodynamic complexities underlying surface enrichment in mixtures. In this work, the surface excess of binary polymer blends is studied as a function of composition and temperature in the vicinity of the critical point. Although the surface excess away from criticality behaves as anticipated, it is found to grow slower than expected as criticality is approached from the one-phase region. These results suggest that the surface and bulk thermodynamics are coupled.