Polymer viscosity in concentrated solutions

Abstract

Our previous theory of polymer viscosity (which completely incorporates hydrodynamic interactions) is generalized to the case of polymer solutions at finite concentration. The specific viscosity of the polymer solution is expressed in a multiple scattering type cluster expansion which is formally in powers of the polymer concentration. We explicitly treat the case of concentrated solutions or the case of undiluted polymers in the absence of entanglements. It is shown that the presence of the other polymers leads to a screening of the intrachain hydrodynamics interactions when the natural size of a free polymer chain becomes on the order of the average volume available per chain in solution. We show how the screening is responsible for the transition from a polymer intrinsic viscosity which varies as M1/2 (M is the polymer molecular weight) in the infinitely dilute limit to a Rouse-like specific viscosity which varies as M in the concentrated limit. It should be noted that the screening cannot be described if the popular preaveraging approximation is employed for the hydrodynamic interactions.