Glass transition temperature and dynamics of α-process in thin polymer films

Abstract

The glass transition temperature T_g and the temperature T_α corresponding to the peak in the dielectric loss due to the α-process have been simultaneously determined as functions of the film thickness d through dielectric measurements for thin films of polystyrene. A decrease of T_g was observed with decreasing film thickness, while T_α 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 the relaxation times of the α-process, not to the relaxation time itself.