INFLUENCE OF BROKEN CONFORMATIONAL SYMMETRY ON THE SURFACE ENRICHMENT OF POLYMER BLENDS

We construct an expression for the free energy of an incompressible binary blend of homopolymers in the vicinity of a hard reflecting surface. Expressed as a functional of the concentration profile away from the surface, we find a contribution to the free energy that is linear in the gradient of the concentration and with a range that extends from the surface a distance of order of the radius of gyration. This term, which was overlooked in previous investigations of wetting phenomena in polymer blends, derives from conformational restrictions on the polymers in the surface layer. An important feature of this nonlocal surface term is to favor an excess of the more flexible component at the surface. In addition, it is capable of influencing the detailed shape of the concentration profile and modifying wetting and prewetting behavior.