The Effects of Inter-particle Attractions on Colloidal Sedimentation

We use a mesoscopic simulation technique to study the effect of short-ranged inter-particle attraction on the steady-state sedimentation of colloidal suspensions. Attractions increase the average sedimentation velocity $v_s$ compared to the pure hard-sphere case, and for strong enough attractions, a non-monotonic dependence on the packing fraction $\varphi$ with a maximum velocity at intermediate $\varphi$ is observed. Attractions also strongly enhance hydrodynamic velocity fluctuations, which show a pronounced maximum size as a function of $\varphi$. These results are linked to a complex interplay between hydrodynamics and the formation and break-up of transient many-particle clusters.