Surface phase inversion in finite-sized binary mixtures

A thin bilayer of two coexisting polymer phases, in contact with a surface which favors and is partially wetted by one of them, was studied by nuclear reaction analysis and phase contrast microscopy. We find that when the less-favored phase is initially in contact with this surface, it is entirely replaced by the partially wetting phase. This inversion evolves with time very differently than in the case of complete wetting. The results suggest that a microscopic surface layer enriched in the surface-preferred component may not be a stable signature of partial wetting in small binary mixtures.