On Crossover Temperatures of Viscous Flow Related to Structural Rearrangements in Liquids.

An additional crossover of viscous flow in liquids occurs at a temperature T vm above the known non-Arrhenius to Arrhenius crossover temperature ( T A ). T vm is the temperature when the minimum possible viscosity value η min is attained, and the flow becomes non-activated with a further increase in temperature. Explicit equations are proposed for the assessments of both T vm and η min , which are shown to provide data that are close to those experimentally measured. Numerical estimations reveal that the new crossover temperature is very high and can barely be achieved in practical uses, although at temperatures close to it, the contribution of the non-activated regime of the flow can be accounted for.