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 format ion of a surface-enriched layer of deuterated polystyrene from a film of a blend with normal (hydrogenated) polystyrene. Three blends are co nsidered: one using a completely miscible blend and two approaching th e coexistence curve from the one-phase region. A simple theory based u pon the assumption that the surface-enriched layer is in local equilib rium with a depletion layer provides qualitative agreement with the da ta. The formation of a wetting layer ''depinned'' from the surface lay er is not observed in the times studied in the experiment.