The effect of temperature gradients on the parameters of Adam-Gibbs model

The most commonly used method for studying relaxation processes in polymers is monitoring the enthalpy recovery by measuring differential scanning calorimetry (DSC) heat capacity data. Because of its great influence on heat capacity data, the effect of temperature gradients in the sample on relaxation dynamics study should be investigated. A model for calculating temperature profile in a DSC sample was proposed previously by combining Fourier's law of heat conduction with the Tool-Narayanaswamy-Moynihan (TNM) model. This model was examined using PS samples with different thicknesses. It was found that the temperature gradient influenced optimized values of the kinetic parameters. The thermal history dependence of model parameters is still prominent, however. Here the Scherer-Hodge (SH) equation (based on the Adam-Gibbs model) instead of the TNM equation, is used for describing the relaxation time-structure-temperature relationship in the temperature profile calculation. It is found that the influence of temperature gradients on the thermal history dependence of the Adam-Gibbs (AG) model parameters is greater than that of the TNM model parameters. But the thermal history dependence of the AG model parameters still exists when the thermal lag effect was incorporated.