New power-law functions describing the temperature and pressure dependences of fragile glass forming liquids

Abstract In this paper, new simple power functions are proposed that describe the dependence of the viscosity (structural relaxation) of glass-forming substances on temperature and pressure. For justification of these functions a simple theory based on the activation model is proposed. The Arrhenius law is the special case of these formulas. The proposed formulas were used to simulate the temperature and pressure dependences of the structural relaxation of a number of fragile substances. It is shown that the suggested functions are in good agreement with the practical dependences. The suggested formulas have several advantages over the currently used Vogel-Fulcher-Tamman function. The suggested formulas provide the better understanding of the nature of processes occurring in glass formers. It is shown that the new functions are a simple and effective tool for investigation the properties of glass-formers. They allow us to find a number of unknown effects. The modeling shows that for some substances the variable fragility is observed.