Mechanisms of rectangular groove-induced multiple-microdroplet coalescences

摘要

The mechanism of microdroplet coalescence is a fundamental issue for droplet-based microfluidics. We devel-oped an asymmetric expansion (a rectangular groove) along one side of a microchannel to achieve multiple-microdroplet trapping, collision, and coalescence. Compared with reported symmetric expansions, this asymmetric groove could eas-ily trap microdroplets and control two or three microdroplet coalescences precisely without a requirement for temporal and spatial synchronization. To reveal the mechanisms of multiple-droplet coalescences in a groove, we observed five different coalescence patterns under different flow condi-tions. Moreover, we characterized the flow behavior quan-titatively by simulating the velocity vector fields in both the microdroplets and continuous phase, finding good agreement with experiments. Finally, a map of coalescence forms with different capillary numbers (0.001