Interdiffusion at the interface of polymeric bilayers: evidence for reptation?

Neutron reflection is used to study the interdiffusion in equal molecular weight polystyrene bilayer melts with a spatial resolution of 10 Å. Interfacial widths and concentration profiles at the bilayer interface are obtained for annealing times up to and beyond the reptation time, τd. For t < τd, the reptation model predicts a mean square displacement of monomers whose time dependence is a power law, the exponent of which changes with time. For the relatively lightweight polymers of M ∼ 233 000, the mean square displacements of monomers is in general agreement with predictions; the permanence of a discontinuity at the interface - which also follows from the reptation model - is observed only for molecular weights M ∼ 1 000 000. © 1991.