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[Math] corresponding to the peak in the loss component of susceptibility due to the [Math]-process and the [Math]-relaxation time [Math] as functions of film thickness d. While the glass transition temperature T_g decreases with decreasing film thickness, T[Math] and [Math] were found to remain almost constant for d > d_c and decrease drastically for d < d_c for high temperatures. Here, d_c is a critical thickness. Near the glass transition temperature, the thickness dependence of T[Math] and [Math] is more prominent. The relation between the fragility index and non-exponentiallity is discussed for thin films of polystyrene.