Antibubbles make a splash Stable air layers that wrap around liquid drops can retain their remarkable geometries a thousand times longer than theory predicts.
atural processes, including increasing droplet viscosity, air sheets team mapped out the parameters needed cloud formation and soil ero- began to envelop the heavy liquids as to produce seldom-seen spherical antision, and technology such they fell into the light oil. After analyz- bubbles on demand. as inkjet printers are based ing several thousand video clips, the At the upper limits of viscosity, the on interactions between droplets and droplets stay connected to the syringe nozzle along long, thin threads of oil surfaces. One area of investigation for “Soap molecules could during the initial impact. When the climate scientists and engineers is low droplet and its long tail enter into the velocity impacts — for example, sec- stabilize the layers, but ondary splashes that occur after the air sheets also wrap around these there are no surfactants pool, primary contact, or drops ejected from structures and produce cylindrical films of air that are stable for thoua boiling interface. These types of col- involved here.” lisions are hard to predict, sands of times longer than as they involve complex expected. physical interactions. When the team used KAUST Research Scienlaser-based interferometry tist Erqiang Li and Professor to scrutinize the cylinders, of Mechanical Engineering they were surprised to see Sigurdur Thoroddsen from the films can become narthe University’s Physical rower than 100 nanomScience and Engineering eters before breaking. Division, along with colAt these scales, stability laborators in France and the theory predicts their disinNetherlands, used advanced tegration in a few microvideo cameras to study drop seconds through the same impacts between different mechanism that breaks up liquids. the water stream running out of faucets. At low velocities, drops tend to either bounce away “Soap molecules could or enter into target liquids stabilize the layers, but there on a thin, hemispherical are no surfactants involved air cushion that eventuhere,” said Thoroddsen. ally ruptures into micro“Our results suggest the stabilization force is the bubbles. The team realized viscous lubrication forces that they might be able within the submicron air to control the geometry of these air sheets if they layer. This shines new light used droplets that are more on thin film instability and viscous. also introduces many more To experiment, the questions.” researchers placed a syringe filled with thick, 1. Beilharz, D., Guyon, A., Li, E. Q., viscous silicone oil a few Thoraval, M.-J. & Thoroddsen, S. millimeters above a pool T. Antibubbles and fine cylindrical When a viscous oil droplet enters into another liquid, an air cushion containing lower-vissheets of air. Journal of Fluid wraps around its long tail and eventually breaks off - creating cosity oil. By gradually free-floating cylinders of air with surprisingly long lifetimes. Mechanics 779, 87–115 (2015).
From curiosity to innovation