NIR light-triggered core-coalescence of double-emulsion drops for micro-reactions

• NIR triggered core-coalescence of double-emulsion drop(DED) for micro-reaction. • A noncontact and controllable strategy was studied for coalescence of droplets. • Continuous core-coalescence with high efficiency and throughput was realized. • Ratio of micro-reaction was tuned by controlling the size of cores in DED. • Two-step core-coalescence of triple-core DED was conducted under NIR irradiation. Microfluidic generated double-emulsion drops(DEDs) with multiple-core are excellent containers for micro-reactions, which can encapsulate kinds of reagents and mix them by core-coalescence. Scaled continuous reactions require controlled coalescence of inner droplets with high efficiency and throughput. Here, we present a non-contact strategy to continuously trigger core-coalescence of DEDs by near-infrared(NIR) light in continuous flow. Under the irradiation of NIR light, the inner core droplets containing prussian blue(PB) rapidly heat up and cavitate, due to the photothermal property of PB. It results that interfacial equilibrium between two inner cores is broken by interface perturbation due to cavitation. The performance of core-coalescence in DEDs is investigated at different PB concentrations, flow rates, and light intensities. Continuous core-coalescence efficiency up to 98 % is obtained in the experiments. We demonstrated that the NIR light-triggered core-coalescence of DEDs provides distinctly microfluidic microreactor for synthesis of copper metal­organic framework (MOF). Moreover, dynamical two-step core-coalescence in the DED with triple-core is conducted under NIR irradiation. The presented technology is amenable to trigger micro-reactions for a wide range of applications such as laboratory-on-a-chip settings, applied chemistry and biomedical engineering.