INITIAL-STAGES OF POLYMER INTERDIFFUSION STUDIED BY NEUTRON REFLECTOMETRY

The time dependence of interdiffusion at the interface between two thin films of deuterated and protonated polystyrene has been investigated by neutron reflectometry. Different time regimes can be resolved. First, a very fast intermixing of chain segments of the originally well-separated molecules over a distance of approximately 3 nm takes place. At intermediate times no significant further movement of the chains across the interface is observed. A third time regime with a larger exponent for the movement of chain segments across the interface is found. It is, however, still considerably slower as compared to the square root of t- behaviour expected at large diffusion times, where the diffusion path is larger than the radius of gyration. Data are analysed with a simple model assuming an error-function-type density profile at the polymer interface, but the general conclusions do not depend on the specific model. Results are discussed in terms of the reptation model of polymer diffusion.