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

4 pages, 5 figures