(230z) Microstructure-Rheology Relationships in Strongly Shear Thickening Colloidal Dispersions

While continuous shear thickening in colloidal dispersions can be quantitatively attributed to lubrication hydrodynamic interactions in strong shear flows(1), questions remain concerning the mechanism(s) underlying discontinuous shear thickening and dilation. To explore this, the shear rheology and colloidal microstructure are measured for a model, near-hard sphere, shear thickening fluid (STF) comprised of near hard sphere silica nanoparticles at high volume fraction (0.52) in PEG/glycol. This suspension exhibits discontinuous shear thickening at stresses above ~200 Pa. The shear and normal stress differences are compared against prior reports(1) and quantitatively compared with the colloidal microstructure using recently expanded stress-SANS rules (2). These measurements provide evidence for the mechanism of shear thickening by relating the microstructure to the flow conditions of the material, and test prevailing ideas concerning the role of specific surface interactions versus hydrodynamic interactions in colloidal dispersions at high concentrations and strong flow conditions.

1. Cwalina, C. D. & Wagner, N.J. â??Material properties of the shear thickened state in concentrated near hard-sphere colloidal dispersion.â? Journal of Rheology. 2014;58:949.
2. Gurnon, A.K. & Wagner N.J., Microstructure and rheology relationships for shear thickening colloidal dispersions. Journal of Fluid Mechanics. 2015;769:242-76.