(532f) Changes to Shear Thickening When Adding Spherical Nanoparticles to Colloidal Slurries

The shear thickening behavior in colloidal dispersions is observed across a range of concentrations and shear rates. In this study, several particle systems in water are examined. First. fumed silica suspensions exhibit irreversible shear thickening behavior when subjected to shear rates exceeding 10,000 s^-1. By using rheology at small gaps (between 30 and 50 μm), high shear rates up to 300,000 s^-1 can be achieved. The shear thickening in fumed silica is affected by concentration, pH, and added salt, as previously discussed in other works. Recently, our research group demonstrated that incorporating spherical silica particles of different sizes (10 and 110 nm) increased the critical thickening shear rate, reduced the magnitude of shear thickening, and resulted in lower final viscosities even at higher total solids concentrations. Addition of spherical silica eventually eliminates shear thickening entirely within measurable ranges (up to 180,000 s^-1). Inspired by the findings from fumed silica, cornstarch solutions were prepared to investigate shear thickening behavior in the presence of charged and uncharged spherical silica nanoparticles. Initial results indicated that adding silica to cornstarch increased the critical thickening shear rate of cornstarch suspensions. Finally, aqueous shear thickening systems of fumed alumina were identified and effects of salt and particle size ratio are being explored.