Chain confinement effects on interdiffusion in polymer multilayers

We have measured interdiffusion in polystyrene on length scales approaching and below the overall dimensions of the polymer molecules, by using neutro n reflectometry to follow the relaxation of the composition modulation in a n isotopic polymer multilayer. After an initial transient, relaxation of th e composition modulation is diffusive, even for times less than the reptati on time. The diffusion coefficient decreases with increasing wave vector, i n qualitative, but not quantitative, accord with theory. [S1063-651X(99)118 01-4].