Kinetics of surface segregation and the approach to wetting in an isotopic polymer blend

We have used neutron reflectometry to study the kinetics of the formation of a surface-enriched layer of deuterated polystyrene from a film of a blend with normal (hydrogenated) polystyrene. Three blends are considered: one using a completely miscible blend and two approaching the coexistence curve from the one-phase region. A simple theory based upon the assumption that the surface-enriched layer is in local equilibrium with a depletion layer provides qualitative agreement with the data. The formation of a wetting layer ''depinned'' from the surface layer is not observed in the times studied in the experiment.