A Study of the Influence of Interparticle Interactions and Hydrodynamic Forces on the Rheology and Shear Stability of Concentrated Colloidal Dispersions and Slurries

The importance of explicitly considering interparticle interactions in the rheology of dense suspensions and particle slurries is well established, although the exact relationships between particle-level quantities and macroscopic rheology and stability are at best qualitative. Most of the understanding has been developed for low shear rheological (linear viscoclastic) properties and/or for dilute dispersions. This project has the goal of providing experimental evidence for the influence of interparticle surface forces and hydrodynamic forces (due to the presence of the solvent) on the moderate to high shear rheological properties and shear stability of dispersions that span the colloidal to particulate range (colloidal dispersions to slurries). Of particular interest is the shear thickening transition and dilatancy, and how that explicitly depends on the strategy used to stabilize the dispersion or slurry (i.e. steric, electrostatic, polymeric stabilization), as well as the hydrodynamic forces important at higher shear rates. The research to date has the following components:

• Systematically explore the influence of the basic methods of particle stabilization on the shear thickening and dilatancy of well-characterized colloidal dispersions and slurries of non-colloidal particles. In this report, in particular, the effect of weak electrostatic stabilization forces on determining the onset and severity of shear thickening is examined.
• Determine the effects of particle size and concentration on the onset and severity of shear thickening.
• Employ this experimental data to test simplified two-particle models for the onset of shear thickening that are derived from simulations and theory.