Effective interaction between active colloids and fluid interfaces induced by Marangoni flows

TL;DR

This paper presents a theoretical analysis of how active colloids near fluid interfaces experience long-range hydrodynamic forces due to Marangoni flows, influencing their self-assembly and dynamics.

Contribution

It introduces a new theoretical framework showing that Marangoni-induced flows cause significant, long-range interactions between active colloids at fluid interfaces.

Findings

Marangoni flows induce long-range forces on active colloids

These forces can dominate over Brownian motion and other interactions

Attractive interactions promote self-assembly into monolayers

Abstract

We show theoretically that near a fluid-fluid interface a single active colloidal particle generating, e.g., chemicals or a temperature gradient experiences an effective force of hydrodynamic origin. This force is due to the fluid flow driven by Marangoni stresses induced by the activity of the particle; it decays very slowly with the distance from the interface, and can be attractive or repulsive depending on how the activity modifies the surface tension. We show that, for typical systems, this interaction can dominate the dynamics of the particle as compared to Brownian motion, dispersion forces, or self-phoretic effects. In the attractive case, the interaction promotes the self-assembly of particles into a crystal-like monolayer at the interface.