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.