Diffusion mechanism for physical aging of polycarbonate far below the glass transition temperature studied by means of dielectric spectroscopy

Dielectric permittivity measurements were used to monitor physical aging of polycarbonate (PC) at about Tg – 100 K. The effect of film thickness and cooling rate from the melt was investigated to give new insight into the microscopic nature of the physical aging process. The results show that both the film thickness and the cooling rate play an important role in the kinetics of physical aging. Indications of a diffusive mechanism for physical aging are given, where free volume holes can disappear either at the external surface of the sample or at an internal surface created during the cooling process. Evidence for the existence of the an internal surface is provided.