Heat capacity in the glass transition range modeled on the basis of heterogeneous dynamics

A heterogeneous version of the Tool-Narayanaswamy-Moynihan (TNM) model is proposed, in which enthalpy relaxation is heterogeneous in the sense that the overall nonexponential relaxation originates from the superposition of independently and exponentially relaxing domains with individual time constants. Analogous to rate exchange at a constant temperature, there is only a single fictive temperature that controls the rate at which all time constants can change considerably during a temperature scan. The model is shown to be consistent with differential scanning calorimetry (DSC) data taken across the glass transition of polystyrene, propylene carbonate, and glycerol. In contrast to the standard homogeneous TNM model, the heterogeneous counterpart fits DSC up-scans for As(2)Se(3) for cooling rates of 0.31, 2.5, and 20 K∕min with a common set of parameters.