Behavior of solutions of hydrolyzed polyacrylamide in shear and converging flows

The viscosity of semidilute aqueous solutions of high-molecular-mass polyacrylamide was examined as a function of the velocity gradient in shear flow in a cylinder-in-cylinder cell and in converging flow at the inlet of a narrow capillary. It was demonstrated that, in shear flow, the viscosity decreased with an increase in the velocity gradient, whereas the effect of the velocity gradient was the opposite in the case of intensely converging flow. A decrease of polymer concentration in solution or the addition of salt reduced these effects. Viscosity variation is controlled by two competing processes: deterioration of the fluctuation network in semidilute solution and uncoiling of macromolecules. In an intensely converging flow, chain uncoiling was found to dominate