Dielectric and Dilatometric Studies of Glass Transitions in Thin Polymer Films

Abstract

Dielectric relaxation and thermal expansion spectroscopy were made for thin polystyrene films in order to measure the temperature $T_α$ corresponding to the peak in the loss component of susceptibility due to the $α$-process and the $α$-relaxation time $τ$ as functions of film thickness $d$. While the glass transition temperature $T_{\rm g}$ decreases with decreasing film thickness, $T_α$ and $τ$ were found to remain almost constant for $d>d_{\rm c}$ and decrease drastically for $d<d_{\rm c}$ for high temperatures. Here, $d_{\rm c}$ is a critical thickness. Near the glass transition temperature, the thickness dependence of $T_α$ and $τ$ is more prominent. The relation between the fragility index and non-exponentiallity is discussed for thin films of polystyrene.