Accidental discovery of identical oil lenses offers insights into emulsions on fluid surfaces

A team of researchers from Universidad Carlos III de Madrid (UC3M) has developed an innovative technique that allows the production of regular oil lenses of uniform size on the surface of water in a simple and reproducible fashion. The technique will facilitate the study of the behavior of oily substances dispersed on water surfaces.

This discovery is crucial for understanding the dispersion of some liquids floating on water and could have many applications in oil spill mitigation and the food and textile industries. The study is published in the journal Physical Review Letters.

The initial discovery, according to the researchers, was the result of an “accident” during the preparation of a routine experiment. “We were trying to coat a water surface with a thin layer of oil, but the result was unexpected: Instead of a uniform film, we obtained a series of identical and very small droplets, which aroused our curiosity,” explains Javier Rodríguez, from UC3M’s Department of Thermal and Fluids Engineering.

To produce the uniform and regular oil lenses, the researchers immersed a glass plate vertically in water. Upon contact with the glass, the surface of the water rose a few millimeters up the plate, creating a kind of liquid micro-toboggan, called a meniscus. Taking advantage of this formation, and using a syringe, they injected an oily substance onto the plate.

This oil, upon touching the water toboggan, was dragged by its own weight, fragmenting into monodisperse liquid lenses of regular shape, as if it were a trickle dripping from a tap. This whole process, explain the authors, was accurately recorded using high-speed cameras (capable of capturing up to 50,000 images per second) to see the details of the rapid fragmentation process of the oil droplets on the water.

“The good thing is that this system, in addition to being inexpensive and reproducible (it can even be recreated in a rudimentary way at home), has many applications,” explains another of the study’s authors, Lorène Champougny, who also carried out this research in the UC3M Department of Thermal and Fluids Engineering and is currently working at the National Center for Scientific Research (CNRS) in Toulouse, France.

“In the environmental arena, for example, it could help us better understand how oil spills are fragmented and dispersed on the ocean surface. This, in turn, could be used to design more effective mitigation strategies,” she adds.

However, its applications also have repercussions in other fields. As the researcher points out, “This discovery could also be used to investigate the treatment of water-repellent surfaces that are used to manufacture waterproof coatings for fabrics such as coats, hiking boots or motorcyclists’ helmets.

“Likewise, in the food industry, it could be used to make lighter and healthier dietary dairy products, such as low-fat butters, by incorporating precise mixtures of water and air into their compositions.”