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

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.