The Flow Properties of Polyvinylpyrrolidone Solutions

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The viscosities of solutions of polyvinylpyrrolidone (=9×105) are determined at 35°C in pure water, in a 0.25 m MgCl2 aqueous solution, in n-propanol, and in a water -n-propanol mixture at several concentrations (0.5–1.5 g/100 ml). Measurements are carried out with a Maron-Belner type low-shear capillary viscometer with various capillary radii (0.0190–0.0761 cm) within the shear stress range of 0.2–20 dyn/cm2 at the capillary wall. The viscosities of the solution show a non-Newtonian flow behavior and a capillary bore-size dependence. The viscosity decreases with the decrease in the capillary bore size within the range of shear stress studied. The results were represented by Ree-Eyring’s generalized flow formula for a flow system containing one Newtonian flow unit and one non-Newtonian one. The contribution of the Newtonian term of the formula to the solution viscosity lowers in viscosity with the decrease in the capillary bore size, whereas the non-Newtonian term makes a contrary contribution. The change in the viscosity of the polymer solution with the size of the capillary tube may be attributed to the changes in the relaxation time of the solvent molecules and in the shear volume of the polymer molecules in the neighborhood of the capillary wall.