Effective forces between colloids at interfaces induced by capillary wave-like fluctuations

TL;DR

This paper calculates the fluctuation-induced forces between colloids at fluid interfaces caused by thermally excited capillary waves, revealing complex dependence on boundary conditions and potential significance in colloid aggregation.

Contribution

It introduces a detailed calculation of Casimir-like forces between colloids at interfaces, highlighting the impact of boundary conditions and separation distance.

Findings

Force decays rapidly at large distances due to cancellation effects

Strong forces at small separations can influence colloid aggregation

Boundary conditions critically affect the magnitude and sign of the force

Abstract

We calculate the effective force mediated by thermally excited capillary waves between spherical or disklike colloids trapped at a fluid interface. This Casimir type interaction is shown to depend sensitively on the boundary conditions imposed at the three-phase contact line. For large distances between the colloids an unexpected cancellation of attractive and repulsive contributions is observed leading to a fluctuation force which decays algebraically very rapidly. For small separations the resulting force is rather strong and it may play an important role in two-dimensional colloid aggregation if direct van der Waals forces are weak.