On scale-dependent effect in laminar flow of dilute polymer solution in tubes

Abstract

Presented are the results obtained in experiments on viscous flow of dilute aqueous solutions of polyethylene oxide in tubes of inner diameter ranging from 0.2 to 8.0 mm. Ostwald viscometers, horizontal capillary viscometers, and two special viscometric setups were used in the measurements. Results have shown that the solution viscosity varies with the changing tube diameter. This effect is not associated with the shear rate dependence or degradation. Laser Doppler anemometers were used to measure the velocity of polymer solutions in thin capillaries. No deviation from the Poiseuille profile was observed. Thus, it is not possible to explain the reduction of viscosity in thin capillaries by means of wall effect. Relationship between scale-dependent effect of viscosity and existence of large macromolecular aggregates is proposed. Anomalies of viscosity are responsible for the ambiguity in the intrinsic viscosity. Intrinsic viscosity, in particular, may be determined by means of the maximum or minimum viscosity. Difference between the maximum and minimum intrinsic viscosities changes with the molecular weight of dissolved polymer. Such differences were not noticed for low-molecular polymers.