Spatially Heterogeneous Dynamics in Supported Ultrathin Poly(ethylene terephthalate) Films Depend on the Thicknesses of the Film and the Adsorbed Layer

The spatially heterogeneous dynamics in supported ultrathin polymer films are widely recognized to explain their unique thickness-dependent physical properties. In this paper, the surface dynamics of supported poly(ethylene terephthalate) films were scaled by the surface crystallization rate to investigate the variations of the spatially heterogeneous dynamics with various thicknesses of the film (h) and the adsorbed layer (h(ads)). It was found that the utmost propagation distance of the substrate effect (h(s)), which increased with h(ads), is a crucial parameter affecting the surface dynamics and determining the spatial distribution of chain mobility in polymer thin films. Either decreasing h or increasing h(ads), to induce h < h(s) causes the surface dynamics to gradually change from the highest undisturbed mobility to greatly suppressed to an eventual uncrystallizable state, corresponding to the fading of the spatially heterogeneous dynamics. These observations will help us to further understand the heterogeneous chain mobility distribution in supported polymer ultrathin films.