Glass transition cooperativity from heat capacity spectroscopy - temperature dependence and experimental uncertainties

The influence of experimental uncertainties of calorimetric parameters from heat capacity spectroscopy on the temperature-dependent glass transition c ooperativity N-alpha from the fluctuation approach is studied. Glass transi tion parameters from 3 omega method and temperature modulated DSC are compa red. The influence of the stationary temperature field on the output of the 3 omega method is studied. Special advantages and disadvantages of 3 omega method and temperature modulated DSC for the determination of glass transi tion cooperativity are discussed. It is confirmed that the temperature-depe ndent cooperativity indicates, independent from experimental uncertainties, a cooperativity onset in the crossover region. The extrapolated onset temp erature T,,, from calorimetry is shown to be comparable with other, indepen dently obtained crossover temperatures for polystyrene and styrene butadien e rubber (SBR 1500). (C) 2001 Elsevier Science B.V. All rights reserved.