Thixotropic yielding behavior of MLPS colloidal suspension

The colloidal suspension of magnesium lithium phyllosilicate (MLPS), a synthetic clay that shows complex rheological behaviors, is a promising analogue for natural soft clay. The significant thixotropy of MLPS colloidal suspension controls the solid-liquid transition and affects the application of the material. In this work, the thixotropic yielding behaviors of MLPS with concentrations of 3, 4, 5, and 6 wt% were investigated utilizing rheological testing methods. The static and dynamic yield stresses measured by different methods were analyzed and compared. The flow curves of shear rate ramp tests show inapplicability in determining yield stresses due to shear banding, while the yield stresses obtained by shear stress ramp and oscillatory shear tests exhibit satisfactory consistency. Coupled with a structural kinetics equation, a thixotropic visco-plastic model incorporating static and dynamic yield stress was established to describe the thixotropic yielding behavior of MLPS suspension. The model parameters were conveniently determined via shear ramp tests and step change in shear rate tests with good fitting performance, and the concentration-dependent characteristics of the parameters were also discussed. Based on model prediction and experimental results, the interactions between shear stress, shear rate, and microstructure were analyzed in steady and transient states.