The effect of molecular structure on interdiffusion of polymer/polymer bilayer films was investigated, Short-time relaxation at poiymer/poiymer interfaces with different molecular weights was also evaluated by in situ neutron reflectivity and analyzed based on various diffusion models. Interdiffusion of cyclic polystyrene/cyclic deuterated polystyrene was investigated as a function of temperature and molecular weight. Cyclic polystyrene, with weight-average molecular weight of 113k, being larger than the critical entanglement molecular weight for linear polystyrene, diffuses twice as fast as the corresponding linear one at all the temperatures employed. This result clearly shows that both the linear and cyclic polystyrenes have the same temperature dependence of segmental frictional coefficient and that the topology strongly affects the molecular motion of the whole chain. Molecular weight dependence of mutual diffusion coefficient of cyclic polystyrene is different from that of the linear one. The shorttime interdiffusion at an interface of linear polystyrene/linear deuterated polystyrene with different molecular weights was examined by time-resolved neutron reflectivity measurements. The model scattering length density profiles obtained by solving a partial differential equation for the diffusion process were used to analyze the data. These analyses reveal that even if the molecular weights of both components are larger than the critical molecular weight for entanglement, the initial interfacial broadening of bilayer films with different molecular weight proceeds with asymmetric mobility being proportional to N-1.
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