Sedimentation path theory for mass-polydisperse colloidal systems

TL;DR

This paper extends sedimentation path theory to analyze how mass-polydispersity affects sedimentation-diffusion equilibrium in colloidal systems, revealing significant impacts near density matching and providing insights into crystallization behavior.

Contribution

The authors develop a theoretical framework for mass-polydisperse colloids under gravity, bridging a gap in understanding polydispersity effects in sedimentation experiments.

Findings

Mass-polydispersity strongly influences sedimentation near density matching.

The theory can be applied to any parent distribution of buoyant masses.

Crystallization behavior in polydisperse systems is affected by sedimentation dynamics.

Abstract

Both polydispersity and the presence of a gravitational field are inherent to essentially any colloidal experiment. While several theoretical works have focused on the effect of polydispersity on the bulk phase behavior of a colloidal system, little is known about the effect of a gravitational field on a polydisperse colloidal suspension. We extend here sedimentation path theory to study sedimentation-diffusion-equilibrium of a mass-polydisperse colloidal system: the particles possess different buoyant masses but they are otherwise identical. The model helps to understand the interplay between gravity and polydispersity on sedimentation experiments. Since the theory can be applied to any parent distribution of buoyant masses, it can be also used to study sedimentation of monodisperse colloidal systems. We find that mass-polydispersity has a strong influence in colloidal systems near density matching for which the bare density of the colloidal particles equals the solvent density. To illustrate the theory, we study crystallization in sedimentation-diffusion-equilibrium of a suspension of mass-polydisperse hard spheres.