Frequency-Dependent Cavitation-Driven Formation of Microbubbles and Nanobubbles under Ultrasonic Irradiation

Acoustic cavitation is a widely used method for generating micronanobubbles (MNBs). However, few studies have examined the formation dynamics of microbubbles (MBs) and nanobubbles (NBs) simultaneously under various ultrasonic conditions. This lack of research hinders our understanding of the correlation mechanisms between different scales of cavitation bubbles during the acoustic cavitation process. In this study, we systematically investigated the size and concentration of MBs and NBs under varying ultrasonic frequencies, powers, and exposure durations. Complementary measurements of zeta potential, temperature, and gas solubility during cavitation were conducted, along with spectral analysis of the acoustic field, to investigate the formation and evolution of MBs and NBs. The results reveal that MBs and NBs have relatively independent formation mechanisms under different ultrasonic conditions. The establishment of a standing wave field and stable cavitation is essential for the formation of MBs. In contrast, the formation of NBs is highly dependent on transient cavitation behavior, particularly under low-frequency and high-power ultrasound.