Surfactant-assisted spreading of an oil-in-water emulsion on the surface of a liquid bath

TL;DR

This study visualizes how an ionic surfactant-stabilized oil-in-water emulsion spreads on water, revealing unique spreading behaviors linked to surfactant properties, with implications for fluid dynamics and surface science.

Contribution

It demonstrates the influence of surfactant properties on emulsion spreading dynamics and visualizes phenomena not previously documented in this context.

Findings

Presence of a transparent area around the oil source

Rapid retraction of oil droplets after source empties

Spreading dynamics depend on surfactant interfacial properties

Abstract

This fluid dynamics video shows how an oil-in-water emulsion stabilized by an ionic surfactant spreads on the free surface of a layer of pure water. The spreading shows two intriguing features: a transparent area surrounding the source of oil droplets, and a fast retraction of the layer of oil droplets on itself once the source has emptied. We show that the dynamics of spreading are strongly connected to the interfacial/bulk properties of the surfactant.