How Dissolved Gas and High-Intensity Ultrasound Are Coupled to Affect Bubble Cavitation.

Bubble cavitation plays a pivotal role in various ultrasound applications, but ultrasound-induced cavitation poses a challenge to our present understanding. Here, we employ both theoretical analysis and molecular dynamics simulations to study the dissolved gas-enhanced cavitation and subsequent evolution of nanoscale cavitating bubbles under high-intensity ultrasound. The simulation results reveal that dissolved gas indeed promotes the formation of cavitating bubbles, which strongly interact with the applied ultrasound. First, the bubble formation causes a significant distortion of the surrounding acoustic field, especially weakening the negative pressure during the negative pressure phase of the ultrasound. Second, the ultrasonic amplitude and frequency, along with the type of dissolved gas, affect bubble evolution via interface-crossing gas transfer. Different responses of CO₂ and CH₄ bubbles to the exerted ultrasound are interpreted by the liquefaction of CO₂ molecules in nanoscale bubbles, the relatively low solubility of CH₄, and the lagging of gas molecule transfer behind the pressure variation.