Mechanism of bubble formation in step-emulsification devices

Step-emulsification device is an emerging technology for bubble generation, which is convenient for numbering-up. However, the mechanism of bubble formation in such devices remains unclear. In this article, the mechanism of bubble formation in step-emulsification devices is investigated by using a high-speed camera. First, the evolution of gas-liquid interface with time during bubble formation is observed. Second, the variation of characteristic parameters of bubbles, such as bubble's volume V-B and generation frequency f, with gas and liquid flow rates is described under various liquid viscosities and step widths. Meanwhile, the coupling law of interface evolution with characteristic parameters of bubbles is explored. Finally, the basic guideline for generation of monodispersed bubbles in step-emulsification is put forward: low liquid viscosity. Connecting the interface evolution with the characteristic parameters, predictive models for bubble's volume, and generation frequency in step-emulsification are proposed, respectively.