A novel surgery-like strategy for droplet coalescence in microchannels

We report an innovative and efficient surgery-like strategy for achieving the coalescence of surfactant-stabilized droplets in microchannels. As pairs of preformed droplets flow across a micro-lancet, with a suitable surface wettability, in a converging microchannel simultaneously, their surfaces are scratched by the micro-lancet, which causes temporarily local scattering of surfactants, and thus induces their coalescence by joining up their scratched wounds. Our approach shows highly controllable flexibility and stability. We demonstrate this by controlling the coalescence of emulsion droplets with different numbers and complex structures. This surgery-like strategy is totally passive and has great potential in myriad applications including micro-reaction, high-throughput injection, and multiple emulsion formation, etc.