Activation Energy for Viscous Flow and Short-Range Order

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Abstract
Viscosity‐temperature properties of many systems are characterized by highly temperature dependent activation energies for viscous flow. It is generally recognized that structural changes taking place in the material as a function of temperature are responsible for this phenomenon. In this paper a formulation of viscosity‐temperature relations is presented in which the structural changes are explicitly taken into account by means of the formalism of short‐range order as a function of temperature. The resulting equation is shown to be a generalization of several semi‐empirical equations in current use. The equation has been applied to several glasses, high polymers, and water and has been found to describe the experimental viscosity data with high accuracy over a wide temperature range.