Viscous fingering in shear thickening silica suspensions

We make an experimental study of the viscous fingering behavior of air displacing shear thickening silica suspensions in linear Hele-Shaw cells with different cell gaps as a function of the injection pressure. The imposed shear rate defined by the ratio of the finger tip velocity and the half of a cell gap, at which the onset of the viscous fingering instability is observed, is close to the critical shear rates of the corresponding shear thickening silica suspensions, irrespective of the cell gap and the injection pressure. The modified Darcy’s law, where the constant viscosity is replaced by the shear dependent viscosity, gives good agreement with the experiments when the imposed shear rate is less than the critical shear rate. When the imposed shear rate is beyond the critical shear rate, the shear thickening silica suspensions give the more negative deviation from the modified Darcy’s law, irrespective of the injection pressure and the cell gap. The relative finger width can be related with non-Newtonian behavior of the silica suspensions.