Studies of the viscosity and sedimentation of suspensions: Part 4. - Capillary-tube viscometry applied to stable suspensions of spherical particles

A description is given of a series of measurements of the viscosity of stable suspensions of spherical particles in an efflux-type capillary-tube viscometer. It is shown that a form of wall-effect is present in the tube, which causes the apparent viscosity of the suspensions to decrease with decreasing tube-size. The suspensions are shown to behave as though a layer of pure liquid were present along the tube walls, though the layer appears to be only hypothetical in nature. The values of the wall-layer thickness obtained in the present work are used in a brief assessment of a recently-proposed "concentration" theory of wall effect. The final values of the relative viscosity, corrected for wall effect, show no dependence on absolute particle size or particle size-range. All series of results are shown to be governed by a single type of equation, which reduces to that of Einstein at very low values of the volume concentration.