Research / Liquid–gas interfaces

Liquid–gas interfaces

Floating particles deform the liquid–gas interface, which drives capillary attraction and aggregation, the so-called Cheerios effect. The deformation depends strongly on particle shape.

With collaborators, we derived a closed-form solution, based on domain perturbations, for the interface around particles of complex, anisotropic shape, including a pinned contact line of varying height.

To test it, I built a fluorescence-based laser-sheet scanning system with stereo imaging that maps the interface with 0.1 mm precision. Measurements around 3D-printed circular, polygonal and undulated particles agree with the model.

Six 3D-printed particles of different shapes floating at a water surface — 3D-printed particles held at the interface: circle, triangle, square, circle with a fourfold undulation, pentagon and hexagon. From Einhorn, Jose, Zigelman et al., J. Fluid Mech. (2025).

Interface height maps around particles, experiment above and model below — Measured (upper half) and predicted (lower half) interface height around a hexagon, an undulated circle and an undulated hexagon. From Einhorn, Jose, Zigelman et al., J. Fluid Mech. (2025).