(518e) Discontinuous Shear Thickening in Dense Suspension of Rough Colloids

The mechanism behind discontinuous shear thickening (DST), in which the viscosity of a dense suspension jumps beyond a critical shear rate, has been recently attributed to interparticle friction. Here, we present experiments and simulations that demonstrate that surface roughness is key to DST and jamming in colloidal suspensions. We synthesize smooth and rough PMMA colloids that are fluorescently dyed and suspend them in a solvent that is refractive index and density matched. Their surface roughness is characterized using atomic force microscopy. Using confocal laser scanning microscopy, we find that the rotational diffusion of rough colloids at high volume fractions is slowed. In addition, rheological measurements show that the surface roughness significantly reduces the critical shear rate required to induce DST. We present a physical rationale behind the translational/rotational dynamics and the DST behavior of these smooth and rough colloids.