On limitations of the viscosity versus temperature plot for glass-forming substances

The plot scaling of viscosity by the reduced temperature as an important and vivid representation of the liquid fragility property has been utilized by materials scientists for more than four decades. In the present manuscript we discuss practical limitations on the high temperature part of the viscosity plot. It is valid up to the boiling point at pressure ranges from the triple point to the critical pressure and nearly up to the critical temperature at high pressure. Although, the high temperature viscosity estimation at T→∞ is rather a result of overestimation of an Arrhenius or VFTH equitation fitting and does not have a physical meaning more attention is required to shed light on the behavior of glass-forming liquids in this temperature range by taking into account the supercritical liquid phenomenon.