Ellipsoidal particles at fluid interfaces

TL;DR

This paper analyzes how ellipsoidal colloids at fluid interfaces experience anisotropic capillary and fluctuation-induced forces, providing analytical and numerical insights into their interactions based on contact angles and thermal fluctuations.

Contribution

It introduces a perturbative method to efficiently compute capillary interactions and analytically characterizes fluctuation-induced forces for ellipsoidal particles at fluid interfaces.

Findings

Capillary forces are anisotropic and significant for micrometer-sized particles.

Analytical expressions for fluctuation-induced forces are derived for different regimes.

Numerical solutions validate the analytical asymptotic behaviors.

Abstract

For partially wetting, ellipsoidal colloids trapped at a fluid interface, their effective, interface--mediated interactions of capillary and fluctuation--induced type are analyzed. For contact angles different from 90$^o$, static interface deformations arise which lead to anisotropic capillary forces that are substantial already for micrometer--sized particles. The capillary problem is solved using an efficient perturbative treatment which allows a fast determination of the capillary interaction for all distances between and orientations of two particles. Besides static capillary forces, fluctuation--induced forces caused by thermally excited capillary waves arise at fluid interfaces. For the specific choice of a spatially fixed three--phase contact line, the asymptotic behavior of the fluctuation--induced force is determined analytically for both the close--distance and the long--distance regime and compared to numerical solutions.