Viscoelastic relaxation in supercooled liquids

Abstract

A study has been made of the viscoelastic behaviour of a range of supercooled liquids each of which has a steady-flow viscosity η fitting the equation, ln η=A′+ B′/(T–T₀), where T₀ is the reference temperature at which no free-volume is available for molecular translational motion. For all the liquids investigated, the limiting shear rigidity modulus G_∞ varies with temperature according to the relationship, 1//_G∞=1//_G0+a₀//_G1(T–T₀), where a₀ is the coefficient of thermal expansion and G₀ the shear modulus at temperature T₀, and G₁ is a shear modulus associated with the weakening of the intermolecular force field due to an increase in free-volume with increasing temperature. The complete linear viscoelastic behaviour can be calculated from a knowledge of the dependence upon temperature of the density, steady-flow viscosity and limiting shear rigidity modulus. Details are given of the new liquid model on which these predictions are based, together with ample experimental confirmation.