The second shear-thinning and strain-stiffening behaviors of bidisperse non-colloidal suspensions

Abstract

Experimental research is done to determine the shear-thinning behavior of a bidisperse non-colloidal suspension under steady-state shear and the strain-stiffening behavior under oscillatory shear. The second shear-thinning behavior is displayed when the volume fraction of the bidisperse particle suspension is between medium and high. It exhibits with an increase in shear rate, the viscosity drops by approximately three orders of magnitude. At low shear rates, a strong particle size dependence of viscosity is observed, while at high shear rates, the particle size dependence is almost non-existent. To further understand the behavior of the second shear thinning, three sets of oscillatory shear tests and steady-state shear tests (constant shear rate) are carried out at three stopping points in parallel using a unique experimental technique we have developed. The values of modulus and viscosity at the third position are significantly smaller than those at the first and second positions. In the oscillatory shear test, the storage and loss moduli of the bidisperse suspension first decrease and then increase as the strain amplitude increases. The particle volume fraction, not the particle size, is closely related to the bidisperse critical strain amplitude. Compared with monodisperse suspension, bidisperse suspension has low viscosity and larger modulus well under steady-state shear and oscillatory shear operations, which is beneficial to the development of new materials and processes. Moreover, by adding a surfactant of a specific concentration to the bidisperse sample, it is proved that the change in the microstructure of the suspension particle is responsible for the rheological properties of the suspension.