| The relationship between the physicochemical properties of colloidal dispersions and the point at which they shear thicken is investigated. A two-particle force balance between the interparticle conservative forces and the hydrodynamic dissipative forces in a concentrated colloidal suspension is constructed to predict the critical shear thickening stress for various electrostatic and near hard sphere dispersions. The force balance is applied to Stöber synthesized colloidal silica dispersions with various particle sizes, concentrations, polydispersities, and electrostatic surface potentials. Dispersions are characterized by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), small angle neutron scattering (SANS), electrophoresis, and rheometry. The success of the model's predictions supports the hydrocluster mechanism for shear thickening. Further evaluation of the microstructure evolution is examined by rheo-optic techniques including: flow small angle light scattering, flow-SANS, and dichroism experiments. These measurements corroborate the formation of hydroclusters during shear thickening, and suggest techniques to tailor a dispersions rheology by modifying constituent particle characteristics. |
