On the Relative Roles of Free Volume and Activation Energy in the Viscosity of Liquids

摘要

The ratehyphen;theory approach of Eyring and the freehyphen;volume theory of Cohen and Turnbull for liquid viscosities have been reconsidered. The rate theory has been reformulated using the Cohen and Turnbull expression for the probability of finding a vacant site and yields an equation of the formeegr;equals;A0explsqb;Ev*sol;RTplus;ggr;V0sol;Vfrsqb;.This result has been applied to many liquids ranging from fused silica to liquid argon and including polyatomic van der Waals as well as hydrogenhyphen;bonded liquids.Consistent fits to both temperature and pressure dependence of viscosity were obtained. A significant conclusion is that the free volume of liquids is considerably higher than that suggested by the WLF and Cohen and Turnbull equations.