Polymer chain diffusion at a temperature below its bulk glass transition temperature

In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in the bulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtained results clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristic length scale of usual segmental motion even at a temperature below its bulk glass transition temperature, T_g ^b. This is consistent with our previous results that the surface glass transition temperature is much lower than the corresponding T_g ^b. Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.