Investigations of anomalous flow with special reference to Thixotropy

Abstract

Absolute viscosity measurements under equilibrium flour conditions have been obtained for thixotropic suspensions of titanium dioxide pigments in linseed stand oils. These cover a range of shear rates and the effects of changes in concentration and temperature have been noted. It is shown that over the complete range there are two components of the shearing stress, one which is independent of temperature and another proportional to the viscosity of the medium as this changes with temperature. The temperature independent term is in the form of a frictional resistance which rises to a limiting value as the rate of shear increases; the other may be regarded as a hydro dynamic viscosity term which decreases to a limiting value with increasing shear. The theoretical significance of the variation in these components with concentration is briefly considered. Thixotropic relaxation has been found to occur in a very complicated way but some approximate measurements on time-dependent viscosities have been made. These indicate how the magnitude and speed of thixotropic change depend upon the equilibrium rate of shear and on concentration.