BROAD-BAND HEAT-CAPACITY SPECTROSCOPY IN THE GLASS-TRANSITION REGION OF POLYSTYRENE

The combination of results from temperature modulated DSC (TMDSC) and 3 omega-method (HCS) in the glass-transition region allows broad band heat capacity spectroscopy in a frequency range of seven orders of mag nitude. In an Arrhenius diagram, the curve for calorimetric data is cl ose 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) < nu < 10(3) Hz and compared with DSC measurements on lin ear cooling (vitrification). The dynamic calorimetric data are obtaine d in the liquid equilibrium state, where the dispersion of the glass-t ransition interval is related to the mean temperature fluctuation of c ooperatively rearranging regions (CRR). As expected from the fluctuati on approach to glass transition, this temperature fluctuation increase s with increasing temperature. This indicates decreasing size of CRRs with increasing temperature. The a = q/delta Tomega parameter is obta ined as a = 6+/-2 from a comparison of thermal and dynamic glass trans ition. (C) 1997 Elsevier Science B.V.