How Capillary Rafts Sink

TL;DR

This paper investigates how capillary rafts, formed by small particles at fluid interfaces, sink depending on particle size, highlighting the role of surface tension and self-assembly in the sinking process.

Contribution

It provides experimental insights into the sinking behavior of capillary rafts and quantifies how particle size influences the sinking mechanism.

Findings

Sinking depends on particle size and surface tension effects.

Capillary rafts sink when particles reach a critical size.

Surface tension significantly alters sinking dynamics compared to Archimedes' principle.

Abstract

We present a fluid dynamics video showing how capillary rafts sink. Small objects trapped at an interface are very common in Nature (insects walking on water, ant rafts, bubbles or pollen at the water-air interface, membranes...) and are found in many multiphase industrial processes. Thanks to Archimedes principle we can easily predict whether an object sinks or floats. But what happens when several small particles are placed at an interface between two fluids. In this case surface tension also plays an important role. These particles self-assemble by capillarity and thus form what we call a "capillary raft". We show how such capillary rafts sink for varying sizes of particles and define how this parameter affects the sinking process.