The glass transition temperature versus the fictive temperature

A comparison of the values of the glass transition temperature (Tg) measured on cooling and the limiting fictive temperature (Tf′) measured on heating as a function of cooling rate is performed for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry (DSC). The results from both techniques indicate that Tf′ is systematically lower than Tg presumably due to the breadth of the relaxation on cooling. The Tool–Narayanaswamy–Moynihan (TNM) model is used to fit the experimental data from dilatometry and DSC in order to ascertain the origins of the higher value of Tg compared to Tf′.