A Molecular Theory of Viscosity of Dilute Polymer Solutions

Abstract

A theory of viscosity is developed on the basis of Born-Green's distribution-function method. The solutions are considered to be composed of solvent molecules and segments of polymer molecules in contrast with conventional models in which solvents are regarded as continuous structureless media. The stress is obtained in terms of two-body distribution functions n a a , n a b and n b b and potential energy functions φ a , φ b and ϕ, where the subscripts a and b refers to solvent molecules and segments, respectively, provided that ϕ refers to interaction between a solvent molecule and a polymer segment. The viscosity and the intrinsic viscosity are obtained from the stress versus strain rate relation. When the solvent is good Staudinger's equation is got. The equation of viscosity [η]=KM α and [η]= A M 1/2 + B M are derived from two simple assumptions for poor solvents. It is, however, impossible to judge which equation for viscosity is more reasonable since the reasoning for any of assumptions is not clear only from the theoretical standpoint.