Tunable Photothermal Bubble Formation in Binary Liquids under Pulsed Laser Excitation

Photothermal microbubbles triggered by pulsed laser heating are critical for diverse applications spanning microfluidics, medical technologies, and materials engineering. Yet controlling their prolonged growth remains challenging due to the intricate interplay between liquid phase transition, dissolved gas diffusion, and convective heat transfer. Here, we systematically examine microbubble expansion in an ethanol-butanol solution by tuning the boiling point and viscosity. Through the variation of the boiling point and viscosity of the binary solution (ethanol/butanol), it was found that the liquid phase transition, dissolved gas diffusion, and convective heat exchange dominated the different growth stages of the micrometer bubbles, respectively. The rapid expansion phase is predominantly influenced by the liquid phase; however, the boiling point plays a crucial role in determining the transition rate between the two phases. A higher boiling point accelerates the transition from rapid expansion to slow diffusion phases, and the viscosity significantly affects the growth rate of bubbles during the slow diffusion phase. In high-viscosity solutions, bubble growth in this phase is influenced by a combination of dissolved gas diffusion and convective cooling of the liquid. Prior studies have concentrated on the immediate bubble growth triggered by pulsed lasers; the outcomes of this study offer insights into forecasting and tuning the evolution of photothermal bubbles.