Study on interdiffusion of polystyrenes of high molecular weight by SANS

The interdiffusion coefficient D_int of polystyrenes of different molecular weights has been measured. The small-angle neutron scattering (SANS) intensity from a sandwich-like sample consisting of alternating deuterated and protonated films is determined as a function of time and analysed with respect to D_int. In the symmetrical case both components have the same molecular weight and interdiffusion coefficients may be scaled according to the reptation theory D ~ M⁻². The WLF (Williams–Landel–Ferry) temperature behaviour is observed. In the asymmetrical case using low- and high-molecular-weight polystyrenes, the interdiffusion is dominated by the faster-moving species. The fast-mode diffusion theory best describes the result. The influence of a non-zero Flory-Huggins interaction parameter χ between deuterated and non-deuterated material has been taken into account showing a significant slowing down for the high-molecular-weight material.