Study of wall effect in flow of polymer solution in capillary

Abstract

AbstractThe flow behavior of a solution of poly(vinyl pyrrolidone) (Mv, 1.0 × 104−9.0 × 105) has been studied at 35°C. in pure water, in 0.25M MgCl2 aqueous solution, in n‐propanol, and in water‐n‐propanol at various concentrations (0.5‐1.5 g. per 100 ml.). The measurements were carried out with a Maron‐Belner low‐shear capillary viscometer with various capillary bore sizes (radius R, 0.0190–0.0761 cm.) within the range of shear stress, 0.2–20 dynes/cm.2 at the capillary wall. The viscosity is 10–30% lower in the smallest capillary bore than in the largest one at the same shear stress. This phenomenon may be attributed to a steric hindrance of the capillary wall to the thermal motion of the polymer molecules near the wall. The results are represented by the modified Ree‐Eyring generalized flow formula, for a flow system containing one Newtonian flow unit and one non‐Newtonian unit, which includes the new additional terms dependent on the capillary bore size. Furthermore, by assuming the existence of wall layer (of thickness d) in the liquid flowing in the capillary tube an equation of the viscosity was derived, and by combining this equation with the aforementioned equation a calculation of the thickness d, where the rate of shear tends to infinity, was attempted.