Temperature dependence of molecular relaxation rates and of viscosity of glass-forming liquids

Abstract Both the Vogel–Fulcher–Tamman and power law equations fit the viscosity and relaxation data of highly viscous liquids, but only over a few decades or over a limited temperature range as T→Tg The two equations strikingly differ at T ≥2 Tg. The former shows an approach towards an Arrhenius behaviour at high temperatures, but the latter shows a point of inflexion. The available data on liquids in the temperature range needed to examine the merits of the two equations do not show this point of inflexion.