Dynamics of colloidal particles with capillary interactions

TL;DR

This paper studies how colloidal particles at fluid interfaces move and cluster due to capillary forces, revealing conditions for observable instabilities and potential experimental applications.

Contribution

It introduces a mean-field model for colloid dynamics driven by capillary interactions, highlighting the instability of uniform distributions and experimental parameter regimes.

Findings

Homogeneous colloid distributions become unstable under capillary attraction.

Large-scale clustering driven by capillary forces is theoretically predicted.

Experimental parameters for observing instabilities are practically accessible.

Abstract

We investigate the dynamics of colloids at a fluid interface driven by attractive capillary interactions. At submillimeter length scales, the capillary attraction is formally analogous to two-dimensional gravity. In particular it is a non-integrable interaction and it can be actually relevant for collective phenomena in spite of its weakness at the level of the pair potential. We introduce a mean-field model for the dynamical evolution of the particle number density at the interface. For generic values of the physical parameters the homogeneous distribution is found to be unstable against large-scale clustering driven by the capillary attraction. We also show that for the instability to be observable, the appropriate values for the relevant parameters (colloid radius, surface charge, external electric field, etc.) are experimentally well accessible. Our analysis contributes to current studies of the structure and dynamics of systems governed by long-ranged interactions and points towards their experimental realizations via colloidal suspensions.