Shear thickening of highly viscous granular suspensions

We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain ${\gamma }_c$ and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics ${\eta }_{\mu }$, dilation ${\eta }_c$ and sedimentation ${\eta }_g$. While ${\eta }_g$ governs the shear thinning regime, ${\eta }_{\mu }$ and ${\eta }_c$ together determine the shear thickening behavior. As the suspending liquid’s viscosity varies from 10 to 1000 cst, ${\eta }_{\mu }$ is found to compete with ${\eta }_c$ and soften the discontinuous nature of shear thickening.