Characteristics of Thixotropic Behavior

Abstract

The shear stress-shear rate behavior of a thixotropic hectorite clay-water suspension was studied in a Couette viscometer under a wide variety of rest and shear rate histories. Shear stress decay and build-up transients resulting from step changes in shear rate were measured. The transient stress data were used to construct equilibrium and constant structure flow curves. The constant structure curves could be described by the Power Law model with a constant exponent but varying coefficient. Normalized stress transients could be described by an exponential time series similar to those used in stress relaxation studies on viscoelastic polymers. This method was applicable to literature data and to data obtained for other fluids in our laboratory. The transient behavior of thixotropic fluids is heavily influenced by past history of deformation. Structural rebuilding during rest seemed to begin with the formation of a weak gel structure. Structural rebuilding was also observed under shear rate. In experiments with a short rest period, stresses measured after reapplication of shear rate returned quickly to the values measured before the rest period.