High-speed imaging of ultrasonic emulsification using a water-gallium system

An emulsification process of water-gallium system during ultrasound irradiation was investigated. Formation of ultrafine droplets occurs when a greatly expanded cavitation collapses near the water-gallium interface and the distance between the droplet and bubble is small. A high-velocity liquid jet makes a cavity in the surface of gallium forcing it to take a crown shape that eventually results in the droplet fragmentation. The above mechanism is supported by a simplified model of droplet formation considering the balance of energy and pressure.