Glass Transition Temperature and Dynamics of $\alpha$-Process in Thin Polymer Films

TL;DR

This study investigates how the glass transition temperature and alpha-process dynamics in thin polystyrene films vary with film thickness, revealing a critical thickness below which significant changes occur.

Contribution

It provides simultaneous measurements of $T_g$ and $T_{ extalpha}$ in thin polymer films, highlighting the thickness-dependent behavior and the role of relaxation time distribution.

Findings

$T_g$ decreases with decreasing film thickness.

$T_{ extalpha}$ remains constant above a critical thickness and decreases below it.

The thickness dependence of $T_g$ relates to relaxation time distribution, not relaxation time itself.

Abstract

The glass transition temperature $T_g$ and the temperature $T_{\alpha}$ corresponding to the peak in the dielectric loss due to the $\alpha$-process have been simultaneously determined as functions of film thickness $d$ through dielectric measurements for thin films of polystyrene. A decrease of $T_g$ was observed with decreasing film thickness, while $T_{\alpha}$ was found to remain almost constant for $d > d_c$ and decrease drastically for $d < d_c$. Here, $d_c$ is a critical thickness dependent on molecular weight. The thickness dependence of $T_g$ is related to the distribution of relaxation times of the $\alpha$-process, not to the relaxation time itself.