(255g) Electrostatics and Friction in Dense Suspensions of Rough Colloids

Although particle roughness is encountered in many technological and engineering applications, its role in the rheology, structure, and dynamics of concentrated colloidal suspensions is not well understood. Previously, our group showed that roughness reduces the onset criteria for shear thickening and dilatancy, in addition to reducing the particle rotational mobility at high volume fractions. Here, we report recent experiments on the viscoelasticity and creep of dense colloidal suspensions comprising of smooth and rough particles. The particles are sterically-stabilized, fluorescent poly(methyl methacrylate) colloids suspended in squalene and a mixture of cyclohexyl bromide and decalin. The role of electrostatic repulsion with respect to frictional rheology is explored using a combination of fast confocal microscopy and rheometry. The microstructure and dynamics of these suspensions will be discussed in light of the rheological phenomena. In particular, preliminary creep experiments suggest that the competition between roughness and electrostatics give rise to tunable strain jump behavior that are reminiscent of large-scale avalanches.