Altering and eliminating irreversible shear thickening of fumed silica slurries using spherical silica

Shear thickening behavior in colloidal dispersions occurs at a wide range of shear rates and concentrations. Using a small gap, parallel plate rheology allows access to shear rates up to 200,000 s⁻¹. Fumed silica suspensions exhibited irreversible shear thickening at critical shear rates above 10,000 s⁻¹, which depended strongly on silica concentration. Introducing 10 nm and 110 nm spherical silica particles to 180 nm fumed silica solutions resulted in increasing the critical thickening shear rate along with reducing the magnitude of thickening. The introduction of sufficient spherical particles to the fumed silica solutions via particle addition at 2 wt% or particle replacement at 7 wt% resulted in no shear thickening or formation of agglomerates. Although shear thickening was tuned by varying the concentration and particle size of spherical silica; hysteresis, i.e., the irreversibility of thickening, remained. In addition, rheo-small-angle light scattering measured the formation of agglomerates greater than 1 μm after shear thickening.