Steady-State and Oscillatory Flow Properties of Polymer Solutions

Abstract

Viscosities, first and second normal-stress differences, and related material functions were determined for steady-state and oscillatory shearing of polyethylene oxide and polyacrylamide solutions by use of a Weissenberg R-17 Rheogoniometer with cone-and-plate shearing geometry. Pressure transducers—located along the radius of the plate, with their 0.04-in-O.D. pressure-sensing membranes flush with the plate surface—were used to determine local values of the normal stress. The sensitivity of the transducers was 20–30 dynes/cm2 for steady-state and 10–15 dynes/cm2 for unsteady-state measurements. The ratio of the secondary to the primary normal-stress difference was negative, was as large as −0.2 for the solutions studied, and appeared to decrease with increasing shear rates over the shear-rate range investigated. Complex viscosity and displacement and amplitude functions for both the primary and secondary oscillatory normal-stress differences were determined as functions of the frequency. A significant improvement in the agreement predicted by the “analogies” between the oscillatory primary-normal-stress-difference functions and the complex viscosity functions was achieved in comparison with previous results by reduction of instrument compliance. The Spriggs four-constant and similar models, as well as the Carreau and Bogue-Chen models, were compared with our steady-state and oscillatory data, and these fit the data fairly well; but overall, the Bogue-Chen model appears to represent the data somewhat better.