SURFACE PHASE-BEHAVIOR IN BINARY POLYMER MIXTURES .3. TEMPERATURE-DEPENDENCE OF SURFACE ENRICHMENT AND OF WETTING

Surface segregation in thin films of binary liquid mixtures consisting of random olefine copolymers was studied by nuclear reaction analysis over a wide temperature and composition range. A divergence of the su rface excess Gamma was indicated as the binodal of each mixture was ap proached from the one-phase region, even at temperatures 100 degrees C below the critical point T-c, and interpreted as the advent of comple te wetting behavior. A consistent description of the adsorption isothe rms in terms of a mean field approach assuming a short-ranged surface potential f(s) is feasible, but requires an unexpected temperature dep endence of f(s). This dependence causes the wetting transition tempera ture to be located lower than expected on the basis of present models. (C) 1997 American Institute of Physics.