Physics: Turning drops back into bubbles

Although bubbles normally burst into droplets, a method to achieve the reverse phenomenon, that is, forming bubbles from droplets, is described in Nature Communications this week. The findings help identify strategies for the manipulation of fluid-fluid interfaces with potential applications in the fabrication of soft materials.

Acoustic levitation is a common technique used to study droplet dynamics by which a droplet can be made to hover in the air under the effect of sound waves. Acoustic pressure has previously been exploited to deform liquid drops by flattening them into a thin film and by inducing buckling.

Duyang Zang and colleagues combine these previously observed effects to achieve controlled bubble formation. They show that a droplet is first deformed into a thin film by acoustic radiation force. Next, the ultrasonic field causes the film to buckle into a bowl shape, which encloses a resonant cavity. The resonance causes the cavity to grow and the liquid interface to curve around it, creating a closed bubble, the authors find.

The observed process might offer an alternative route to bubble formation, which could have applications in foam preparations in the food, cosmetics and pharmaceutical industries.

doi: 10.1038/s41467-018-05949-0

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