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

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.