The interdiffusion of long polymer chains at the interface of two melts has been studied as a function of time by neutron reflection. The time range studied spanned from the time characteristic of the motion of the single segment (Rouse time, ${\mathrm{\tau }}_{\mathit{e}}$) up to the time at which the center of mass of the whole molecule has moved a radius of gyration (reptation time). At least for t>${\mathrm{\tau }}_{\mathit{e}}$, the diffusion rate slows down with time until the bulk diffusion rate is reached, in agreement with the current theories for the motion of a polymeric chain in a melt.

• Received 27 June 1990

DOI:https://doi.org/10.1103/PhysRevB.42.6846