19] Rotating cylinder viscometers

Abstract

The floating rotor viscometer has found widespread use for studying the viscosity of deoxyribonucleic acid (DNA) solutions under conditions of low shear and for examining different types of non-Newtonian behavior, such as the increase or decrease in viscosity with change in shearing force or time of shear. In the past few years, this viscometer has also been used to study the shear-dependent viscosity of certain protein solutions. The viscosity of a solution, measured in poises, is simply the ratio of the shear stress exerted on the solution, in dynes/cm 2 , divided by the shear rate, in sec –1 . Rotating cylinder viscometers can either fix the shear stress and measure the shear rate or fix the shear rate and measure the shear stress. The latter type includes viscometers where either the inner or the outer cylinder is rotated, and the stress on the opposing cylinder is measured directly. These viscometers are usually complicated in construction and are designed for specific applications. Some incorporate a guard ring for circumventing the problem of surface films when working with protein-containing solutions. Others measure the rheological properties of blood by providing special geometries so that normal stresses and time-dependent phenomena can be investigated.