Abstract
The glass transition temperature Tg and the temperature Tα 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 Tg was observed with decreasing film thickness, while Tα was found to remain almost constant for d > dc and decrease drastically for d < dc. Here, dc is a critical thickness dependent on molecular weight. The thickness dependence of Tg is related to the distribution of the relaxation times of the α-process, not to the relaxation time itself.
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