Abstract
The dependence between the calorimetric glass transition width ΔTg defined in heat capacity curves and structural relaxation dynamics is studied in analytical and experimental fashions. The Tool–Narayanaswamy–Moynihan–Hodge model is analyzed to extract the relations between the normalized glass transition width ΔTg/Tg and three dynamic parameters: fragility (m), stretching exponent (βKWW) and non-linear factor (x). When the other two dynamic parameters are fixed, ΔTg/Tg is found to scale linearly with 1/m or 1/βKWW, but not to show marked variation with x in the range of practically accessible values. Experimental data of more than 50 glass formers covering molecular, metallic and oxide systems are examined, and the linear relations are reproduced for m (or βKWW) among the chemicals of comparable βKWW (or m). Joint consideration of m and βKWW makes an empirical equation of ΔTg/Tg=2.20*(1/m+0.0026)*(1/βKWW−0.59) with high accuracy for all the materials. For the glass formers with similar βKWW, Moynihan's relation can be approximately restored.
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