Thixotropy of Mg–Al-layered double hydroxides/kaolinite dispersion

The rheological characteristics of Mg–Al-layered double hydroxide (LDHs)/kaolinite dispersions were investigated as a function of pH and mass ratio of LDHs to kaolinite (R). The stress ramp and stress sweep experiments were used to measure the yield stress of the dispersions. In both experiments, a critical shear stress (τc) was obtained at which the viscosity decreased by 3–4 orders of magnitude. The τc value decreased first and then increased with the increase of the R, showing a minimum at R = 0.05. The linear oscillatory shear experiments and the thixotropic loops experiments were performed to investigate the thixotropic behavior of the dispersions. The complex thixotropy was observed with the linear oscillatory shear experiments, and it was found that the thixotropic type of the LDHs/kaolinite dispersions may be affected by R in the range of 0–0.35 and pH value in the range of 3–12. With the increase of R or pH value, the thixotropic type of LDHs/kaolinite dispersions transformed from positive thixotropy to complex thixotropy. By comparing the results of the thixotropic loops experiments with those of the linear oscillatory shear experiments, it was demonstrated that thixotropic loop of complex thixotropy had a crossover point that divided the loop into two sections.