Mesoscale effect on bubble formation in step-emulsification devices with two parallel microchannels

The step-emulsification devices with parallel microchannels are promising for the high-throughput formation of bubbles. However, the mechanism for bubble formation in such devices remains unclear. In present study, the mesoscale concept of compromise in a competition is used to reveal the mechanism. Nitrogen is used as the dispersed phase, and aqueous solutions with different viscosities are used as the continuous phase. The flow patterns and characteristic parameters for bubble formation are studied by using a high-speed camera. The characteristic parameters include the head distance of gas-liquid interface and the neck width, and the size and formation frequency of bubbles. Bubble formation is affected by the hydrodynamic feedback in the chamber and the interfacial evolution process, characterized by the relative magnitude of the evolution velocity for the head distance and the neck width of gaseous thread in both microchannels. It is found that the compromise effect is beneficial for the formation of bubbles with excellent monodispersity.