Confirmation of a calorimetric peculiarity in the crossover region of glass transition in poly( n-hexyl methacrylate) by differential scanning calorimetry

Abstract

The Narayanaswamy model for vitrification is modified to deliver local information about the underlying equilibrium trace of calorimetric response in an Arrhenius plot. The analysis of a simple differential scanning calorimetry (DSC) thermogram for polystyrene reproduces the calorimetric equilibrium trace from heat capacity spectroscopy with an accuracy of few tenths of a frequency decade. Further, contour maps for linear dielecric, heat capacity, and shear response in the crossover region of dynamic glass transition in poly( n-hexyl methacrylate) are presented. The calorimetric map has a saddle between the death of the high-temperature process ( a) and the onset of the low-temperature process ( α). The sigmoid bend in the equilibrium trace near this peculiarity can independently be confirmed by the modified Narayanaswamy model evaluation of a simple DSC thermogram. A speculative, free-volume physical picture of the crossover region is described.