The Effects of Inter-particle Attractions on Colloidal Sedimentation

TL;DR

This study uses mesoscopic simulations to explore how short-range inter-particle attractions influence the sedimentation behavior of colloidal suspensions, revealing complex effects on velocity and fluctuations.

Contribution

It provides new insights into the impact of attractions on sedimentation dynamics and fluctuation phenomena in colloidal suspensions.

Findings

Attractions increase sedimentation velocity compared to hard spheres.

Non-monotonic velocity dependence on packing fraction with a maximum at intermediate densities.

Hydrodynamic velocity fluctuations are significantly enhanced by attractions.

Abstract

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 $\phi$ with a maximum velocity at intermediate $\phi$ is observed. Attractions also strongly enhance hydrodynamic velocity fluctuations, which show a pronounced maximum size as a function of $\phi$. These results are linked to a complex interplay between hydrodynamics and the formation and break-up of transient many-particle clusters.