Waves create backwards bubble
Researchers have used sound waves to create a bubble from a drop of water.
Bubbles normally pop and burst into lots of little liquid drops, but Australian and international researchers have flipped this process on its head, forming bubbles out of liquid drops using nothing but sound.
Acoustic levitation is a common technique used to study droplet dynamics by making a droplet hover in mid-air under the effect of sound waves.
Acoustic pressure has previously been used to squash liquid drops into a thin, flat film by inducing buckling.
Now, researchers have combined these previously observed effects to achieve controlled bubble formation.
In the experiment, 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 process can be seen in the videos below.
The experts say the technique could be used in the manipulation of fluid-fluid interfaces, and has potential applications in the fabrication of soft materials.