CRITICAL-POINT WETTING FROM BINARY POLYMER MIXTURES

Critical point wetting generally occurs whenever a binary fluid system in the demixed region of phase space, in contact with a surface, appr oaches its critical temperature. For the case of polymeric mixtures th e segmental interaction parameter, which determines the interfacial te nsion between the coexisting phases, can be very low even far from the critical point. This suggests that polymer blends should be likely ca ndidates to exhibit complete wetting even far below the critical point . Using nuclear reaction analysis, we have now observed such complete wetting behaviour from two different classes of binary polymer mixture s. These are mixtures of statistical olefinic copolymers, with slightl y different chemical microstructures; and an isotopic pair of deuterat ed and protonated polymers. In the former case we have been able to fo llow the growth with time t of the wetting layer thickness l; our resu lts indicate l approximately log t.