Broad band heat capacity spectroscopy in the glass-transition region of polystyrene

Abstract

The combination of results from temperature modulated DSC (TMDSC) and 3ω-method (HCS) in the glass-transition region allows broad band heat capacity spectroscopy in a frequency range of seven orders of magnitude. In an Arrhenius diagram, the curve for calorimetric data is close to that of dielectric data, except from some remaining problems of temperature calibration. The dynamic glass-transition temperature and the width of the transition interval are determined in the frequency range 10 −4 < ν < 10 3 Hz and compared with DSC measurements on linear cooling (vitrification). The dynamic calorimetric data are obtained in the liquid equilibrium state, where the dispersion of the glass-transition interval is related to the mean temperature fluctuation of cooperatively rearranging regions (CRR). As expected from the fluctuation approach to glass transition, this temperature fluctuation increases with increasing temperature. This indicates decreasing size of CRRs with increasing temperature. The a = q δT∗ω parameter is obtained as a = 6±2 from a comparison of thermal and dynamic glass transition.