The viscosity of suspensions of large, nonspherical particles in polymer fluids

Abstract

Equations are derived which describe the viscosity of suspensions of nonspherical particles in high-viscosity polymer fluids. The viscosity increase over that of the medium is evaluated using a model system of prolate and oblate spheroids which can exist in the suspension as singlets, doublets, etc., up to large agglomerates. The important energy-dissipating terms involve the work to rotate all the “free” particles in the viscous medium and the work required to disrupt agglomerates. The latter depends on the frictional force between particles, the magnitude of which is determined by a closeness-of-approach or interaction parameter which can be interpreted as a measure of fluid immobilization at the particle surface. The equations thus derived are of the same form as those proposed by Goodeve and describe the viscosity versus shear rate behavior for dispersions of many rodlike and platelike particles in various polymer fluids. They are also applicable to dispersions of nonelongated magnetic materials which tend to form agglomerates because of magnetic particle-to-particle attraction.