Rough colloids in shear flow: transient and steady state rheology

Although particle roughness is encountered in many technological and engineering applications, its role in the rheology of concentrated colloidal suspensions is not well understood. Here, we present experiments and simulations that demonstrate that surface roughness is key to shear thickening and jamming in colloidal suspensions. We suspend smooth and rough colloids in a solvent that is refractive index and density matched. The surface profiles of the colloids are characterized using atomic force microscopy. We recently developed state diagrams that characterize the transition from continuous to discontinuous shear thickening in flowing suspensions when the roughness is increased above a critical value [Hsiao et al., PRL 158001, (2017)]. A physical rationale behind these observations is presented by considering the competition of lubrication and friction in suspensions of rough colloids. Futhermore, we investigate the creep and strain recovery of these suspensions. At volume fractions below the hard sphere glass transition, rough colloids impart rheological properties that are reminiscent of colloidal glasses and granular materials.