Formation of magnetic ionic liquid-water Janus droplet in assembled 3D-printed microchannel

Droplet-based microfluidics offers an effective approach for overcoming the drawbacks of high viscosity and costs of ionic liquids (ILs) in practical applications. However, studies on the hydrodynamic behavior of the formation of IL-based Janus microdroplets which can facilitate the multifunctional applications of ILs through unique structures, are still limited due to their complex interfacial properties and high viscosities. Here, magnetic ionic liquid (MIL)-water Janus droplets were generated in an assembled co-flowing 3D-printed microchannel. Seven typical flow patterns of MIL-water Janus droplet generation were presented in a mountain-shaped flow pattern diagram, which was compared to the flow regime demarcations of MIL single-phase droplet formation. The scaling law of MIL-water Janus droplet size was analyzed to further reveal the breakup mechanism of biphasic dispersed phases with large differences in viscosities and interfacial tensions. Besides, the morphology control of surfactant-free MIL-water Janus droplet in the microchannel was investigated qualitatively and quantitatively. And, by changing the continuous phase, the morphology evolution of MIL-water Janus droplet to core-shell structure was also observed. The present study would be useful for providing a deep and comprehensive understanding on the formation and structure control of IL-based Janus microdroplets which are promising candidates for the use in applications of catalysis and extraction.