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

The Narayanaswamy model for vitrification is modified to deliver local info rmation about the underlying equilibrium trace of calorimetric response in an Arrhenius plot. The analysis of a simple differential scanning calorimet ry (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 saddl e between the death of the high-temperature process (a) and the onset of th e low-temperature process (alpha). The sigmoid bend in the equilibrium trac e near this peculiarity can independently be confirmed by the modified Nara yanaswamy model evaluation of a simple DSC thermogram. A speculative, free- volume physical picture of the crossover region is described. (C) 1999 Else vier Science B.V. All rights reserved.