The effects of particle-size on reversible shear thickening of concentrated colloidal dispersions

The particle size dependence of the reversible shear thickening transition in-dense colloidal suspensions is explored. Five suspensions of monodispers e silica are synthesized via the Stober synthesis. The physicochemical prop erties of the dispersions are quantified using transmission electron micros copy, dynamic light scattering, small angle light scattering, electrophores is, and viscometry. Rheology measurements indicate a critical stress markin g the onset of reversible shear thickening that depends on the dispersion's particle size, concentration, polydispersity,:and interparticle interactio ns. A simplified two particle force balance between the interparticle repul sive forces and the hydrodynamic compressive forces is used to derive a sca ling relationship between this critical shear stress and the suspension pro perties. The scaling is tested against the fully characterized silica dispe rsions, which span nearly a decade in particle size. Furthermore, bimodal m ixtures of the dispersions are employed to evaluate the accuracy of the sca ling to predict the critical shear stress for dispersions with varying degr ees of polydispersity. The success of the scaling supports the hydrocluster mechanism for shear thickening and suggests methods for controlling shear thickening by tailoring particle properties. (C) 2001 American Institute of Physics.