Viscosity of Entangled Polymers; Theory of Variation with Shear Rate

Abstract

The very high viscosity of melt polymers caused by entanglements decreases with shear rate. A theory for this effect, based on the ideas of Graessley, is presented. It uses the fact that, at high shear rates, the time needed to form entanglements is larger than the transit time of a group of segments over a potential entanglement site. As a result, entanglements do not have time to form and the viscosity is decreased. Account is taken of the fact that entanglements of various complexity have different formation times. This effect is combined with previous viscosity theory to give an equation relating viscosity to shear rate. It agrees well with the literature data for monodisperse polystyrenes and gives the same general shear‐rate dependence as Graessley has found by a somewhat different method.