Modeling photoacoustic cavitation nucleation and bubble dynamics with modified classical nucleation theory

Photoacoustic cavitation (PAC) is the formation of bubbles in liquids using a focused laser and a pre-established ultrasound synchronously. The decreased threshold of each modality and the precise location of cavitation determined by the focused laser are both significant in the targeted theranostics. In this study, PAC nucleation was described using the modified classical nucleation theory by Kashchiev's scaling function. A two-stage model of the PAC bubble dynamics was presented based on the two different bubble behaviors. It was clarified that both negative acoustic pressure and laser-induced temperature rise, resulting in the decrease in critical radius and the increase in nucleation rate, and thereby contribute to the increase in nucleation probability in the confocal region. Ultrasound determined the whole PAC bubble dynamics with temperature-dependent parameters, while the laser mainly contributed to its initial conditions. Moreover, the effects of certain parameters on PAC were further discussed, including the relative acoustic phase when a laser is introduced (φ), laser pulse duration (τ_L), laser focus radius (R_f), and ultrasound amplitude (P_A). The model would be helpful in understanding the PAC process and further in introducing PAC to potential targeted theranostics.