Aging effects on the thermal expansion coefficient and the heat capacity of glassy polystyrene studied with simultaneous measurement using temperature modulation technique

Aging effects on the glassy polystyrene were studied with simultaneous measurement of the complex thermal expansion coefficient and the complex heat capacity. Aging period was changed from 10 to 100 h at 90 °C. It was found that the stepwise change in the real part of the complex thermal expansion coefficient and the peak of the imaginary part occurred at lower temperature than those of the complex heat capacity in all cases. As the aging period increased the stepwise change in the real part shifted to the higher temperature and sharpened. A qualitative model based on the energy landscape picture is proposed.