On the use of relaxation times for comparing ultraviscous liquid dynamics
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In studies of ultraviscous liquids and glasses, (i) the relaxation time and its temperature dependence are generally compared without regard to its asymmetric distribution and (ii) the calorimetric relaxation time at T(g,DSC), the onset temperature of the specific heat rise in a heating scan at 20 K/min, is arbitrarily chosen as 100 s and compared against the relaxation time determined by spectroscopy. We propose that the relaxation time and its derivatives should be compared in a fixed frame of reference, preferably by using its average value that takes into account the asymmetric distribution, and we show that the relaxation time at T(g,DSC) is a material characteristic. It varies with the extent of nonexponential and nonlinear relaxation and the activation energy.
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