Air bubbles play a role in shear thinning of non-colloidal suspensions

Abstract

Shear thinning of non-colloidal suspensions involving multi-scaled air bubbles is studied. It is observed that the presence of bubbles significantly affects the transition and equilibrium rheological behavior. Large bubbles enhance shear thinning of the system by increasing the particle loading at low shear rates, whereas nano-bubbles suppress shear thinning by introducing additional repulsive interactions between smooth solid spheres, which also hinder the shear thinning of the polymeric matrix at high shear rates. As to the transition behavior at low shear rates caused by the particle organization, nano-bubbles induce a more diffusive particle motion, leading to a larger critical strain accounting for the finish of the organization process. It shows that nano-bubbles shield the interaction between solid spheres. Therefore, a degassing process prior to the rheological experiment is essential in order to achieve reliable rheological properties of the two-phase suspension system.