Generation, control, and application of stable bubbles in a hypersonic acoustic system†

Bubble-based microfluidics has been applied in many fields. However, there remains a need for a facile and flexible method for stable bubble generation and control in a microchannel. This paper reports a hypersonic acoustic system that can generate and release functional stable bubbles in a microchannel in an on-demand manner. It was found that the hypersonic frequency in this system played a vital role in the generation and control of bubbles. Specifically, a nanostructurally enhanced acoustic resonator was used to generate highly localized ultrahigh-frequency acoustic waves that ensured the feasibility and rapidity of bubble generation. Simultaneously, the acoustothermal effect of hypersound was harnessed to effectuate precise control over the bubble size. In addition, high-throughput droplet splitting was performed to confirm the stability of bubbles and their functionality in micromanipulation. The results showed that a mother droplet could be split controllably into a desired number of daughter droplets with specific volume ratios. In summary, the hypersonic acoustic system was demonstrated to be capable of on-demand-generation of stable bubbles in a microfluidic context and thus may extend the bubble-based applications.