| Abstract
| - Surface mobility in polystyrene (PS) films was studied using (PS/deuterated PS) bilayerfilms, which were prepared by attaching original two surfaces together. Time evolution of the bilayerinterface at various temperatures was examined by dynamic secondary ion mass spectroscopy inconjunction with neutron reflectivity. When the bilayer was annealed at a temperature above bulk glasstransition temperature, Tgb, the interfacial thickening was well expressed by the context of Fickiandiffusion. On the other hand, in the case of an annealing temperature above surface glass transitiontemperature, Tgs, and below Tgb, the interface monotonically thickened with the time at first and thenturned to be independent. This means that chains went across the “mobile” interface and then reachedthe “dead” bulk region in which the diffusivity should be frozen. Hence, it was claimed that chains coulddiffuse discernibly in the surface region even at a temperature lower than the Tgb. On the basis oftemperature and molecular weight dependences of quasi-equilibrium interfacial thickness after asufficiently long time, a possible model of mobility gradient in the surface region was proposed.
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