Glass transition temperature its exploitation and new conception of fragility
Relations between the magnitude of the change of the ratios of crystallization and melting temperature with glass transition temperature, that is Tc/Tg and Tm/Tg, determine the order of the values of relative change of glass stability (GS) parameters dKH/KH, dKW/KW and dKLL/KLL. The linear correlation of new GS parameters FK and FKA which include fragility and reduced glass transition temperature with logRc is a better correlation of KLL. The stretching exponent increases as a linear function of T/Tg in the interval 1≤T/Tg<1·1 for given values of the dynamic fragility parameter m. As result, it follows that the kinetic term in fragility can be neglected. The thermodynamic term, which has a dominant role in fragility can be determined by the expressions for configurational entropy and configurational heat capacity. We compared Sc(T) a function of temperature dependence of configurational entropy which was obtained by Sipp et al and ScVFT (T) a function proposed by Yue. Both Sc(T) and ScVFT(T) have the same temperature dependence and almost overlap. Therefore, using either Sc(T) or ScVFT(T) we will get the same value of fragility index. From the dependence of lnSc(T) versus lnT it is possible to successfully predict the relations between the values of m for different glass formers.
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Document Type: Research Article
Publication date: December 1, 2018