Surface segregation from polystyrene networks

We have used neutron reflectometry and carbon and neon forward recoil spect rometry to measure the surface segregation of deuterated polystyrene from a hydrogenous polystyrene network. We find that when the linear polymer is o f a high molecular weight (similar to 600 000), the surface segregated prof ile can be predicted by mean field theory. In these systems the segregation is a rather slow function of time, reflecting the large number of entangle ments in such crosslinked mixtures. When the deuterated polystyrene is of a lower molecular weight (similar to 100 000), the surface segregated layer does not evolve monotonically with time but the shape of the profile can be predicted by mean-field theory. However, when the network is significantly crosslinked, the linear polymer is expelled from the network.