Analysis of TNM model calculation for enthalpy relaxation based on the fictive temperature model and the configurational entropy model

Abstract

Enthalpy relaxation experiments were conducted for polystyrene samples at different annealing temperatures below glass transition temperature (Tg) using a differential scanning calorimeter. The framework of Tool-Narayanaswamy-Moynihan approach was applied to reproduce experimental traces with two models of the structural relaxation times; those are the generalized Arrhenius type characterized by fictive temperature (Tf model) and the configurational entropic type (Sc model). The calculation data of the heat capacity (cp) obtained from the two models were analysed on the basis of the parameter – geometry relationship, in which three factors were given to the geometry of the Tg shoulder and overshoot appeared in cp curve. It was found that both the horizontal shift and the broadening of Tg shoulder occur interdependently in the cp curve calculation of Sc model, while they are almost independent in the calculation of Tf model. In addition, the analysis revealed the process of producing cp overshoot in Tg shoulder, which is expected to be instructive in the optimized cp calculation.