Preventing shear thickening in granular suspensions by enhancing hydrodynamic interactions

As a critical volume fraction is approached, granular suspensions can increase their viscosity dramatically under rapid shear; i.e., they exhibit Discontinuous Shear Thickening (DST). Previous works show that this phenomenon is related to frictional particle interactions and the formation of force chains that span the system, similar to dry granular materials. However, frictional contacts can be possibly reduced by lubrication. We experimentally studied the flow dynamics of dense granular suspensions in highly viscous liquids. By combining rheological measurements and fast imaging techniques, we characterized the flow curves for different liquid viscosities $\eta_0$. We found that shear thickening becomes weaker with $\eta_0$ and eventually disappears for highly viscous solvent. In this regime, the suspensions show a Newtonian-like behavior with constant viscosity under shear. The crossover from granular to Newtonian regimes reflects the competition between friction and hydrodynamics.