Temperature variation of viscosity and the structure of liquids

Abstract

The ratio a of the energy of activation of viscous flow to the energy of vaporization at the same temperature is determined for a large number of liquids of diverse types. For all but a relatively small number of molecules approching most closely to spherical shape, the ratio is found to be sensibly constant for non-associated liquids, and is independent of size, shape, and polarity. The significance of this constancy is discussed in terms of a simple flow model. High values of a appertain for liquids known to be associated through the formation of intermolecular hydrogen-bonds, and it is argued that the viscous flow process does not in itself lead to rupture of such bonds.