Control of photothermal liquid jets through microbubble Regulation: Fundamental mechanisms and Developing Strategies

Plasmon-induced photoacoustic streaming, considered as a potential application for micro-pumps in microfluidics, currently encounters ongoing debates concerning its fundamental mechanisms. In this study, we investigate the crucial role played by microbubbles in generation of jets in an ethanol aqueous solution. The power density threshold for bubble generation and its dependency on jet initiation are confirmed and the microbubble behavior is well regulated by manipulating the laser and liquid properties. Through simulations coupling fluidic and thermal fields, the significant role of Marangoni effect is validated in jet formation. Specifically, the temperature gradient of microbubbles is determined to be a pivotal factor in the generation of collimated jets. Additionally, factors influencing jetting, such as microbubble size and temperature gradients are studied, and noticeably, a stabilized jet lasting over 4 h is achieved based upon.