The application of temperature-modulated DSC to the glass transition region: II. Effect of a distribution of relaxation times

摘要: Abstract An analysis of temperature-modulated differential scanning calorimetry (TMDSC) in the glass transition region is presented. It extends an earlier and simpler model by introducing a distribution relaxation times, characterised Kohlrausch–Williams–Watts (KWW) stretched exponential parameter β, addition to usual kinetic parameters relaxation, namely Tool–Narayanaswamy–Moynihan (TNM) non-linearity x apparent activation energy Δh∗. The present describes, more realistically than did its predecessor, all characteristic features TMDSC region, it has been used examine effects important experimental variables, period modulation underlying cooling rate. shown that, for typical conditions practice, likely that there well be interaction between vitrification process, due rate, dynamic whereby complex heat capacity C p ∗ shows sigmoidal decrease temperature range dependent on frequency. Accordingly, care must exercised quantitative evaluation data suggestions are made regarding optimum procedures this respect. Also, comparing rate required define same conventional DSC , respectively, correspondence them obtained which allows magnitude fluctuations Donth’s fluctuation dissipation theorem evaluated. Finally, β have similar curves, but very different little effect significant broadening as decreases. argued breadth therefore provides measurement independent value x, thus resolving problem existed some years.