(268a) Controlling Shear Thickening in Colloidal Dispersions By the Addition of Shaped, Non-Colloidal Particles

Colloidal dispersions exhibit shear thickening and it is often desirable to control the onset and extent of this rheological response. While tailoring particle size, shape, surface interactions, and solvent properties can all be used to systematically and predictively vary the shear thickening behavior of a suspension, it has been shown that confinement can also affect suspension rheology due to the enhanced hydrodynamic interactions propagated by the confining surfaces (Swan & Brady, JFM 2011). Simulations of non-Brownian particles with models for hydrodynamic interactions have also shown that confinement can induce shear thickening (Bian et al. JNNFM 2014). Here, we exploit these results to control reversible shear thickening in colloidal dispersions by inducing confinement within the suspension by adding non-colloidal particles. For example, it has also been demonstrated experimentally that shear thickening in colloidal dispersions can be dramatically altered by the addition of non-Colloidal spherical and cubic particles to the suspension (Cwalina et al. JOR 2015, AIChE 2017). At low volume fractions, the addition of non-colloidal spherical particles to the colloidal dispersion leads to an increase in the steady shear viscosity as well as the dynamic moduli. At higher volume fractions of non-colloidal spheres, the shear thickening power law exponent increases with the addition of non-colloidal particles. At higher concentrations of added, cubic particles, deviations from this shifting procedure are apparent as depletion attractions and confinement of the underlying colloidal dispersion lead to larger increases in the viscosity at both low and high applied shear stresses. Further effects are induced by the greater confinement afforded by adding large plate-like clay particles even at very low concentrations. The results of this study provide guidance for formulating suspensions through control of particle shape and mixture concentration. Examples of the use of this effect in technologies will be given.