Gradient and Time Dependence of Viscosity of Polymer Solutions in Very Viscous Solvents

Abstract

Solutions of high molecular weight linear polymers in very viscous solvents exhibit two peculiar effects even at rather low concentrations. With increasing gradient the viscosity first drops to a minimum and then increases over a wide gradient range. Moreover, prolonged shearing at constant gradient induces an increase of viscosity which dependent on concentration and gradient either continues with steadily decreasing slope or after a while turns over into a gradual decrease with a finite limit not much different from the starting value. The first effect is partly due to an actual increase of intrinsic viscosity with increasing gradient and partly to the time effect. The former contribution is proportional to the concentration, the latter to the second or higher power of concentration. Both effects occur with the polymer improved lubricating oils.