LAUSR

Abstract Double emulsion droplets are of enormous potential application value in the fields of medicine, chemical and energy. Understanding of the coupling behavior of the two layers of interface in the process of compound jets breakup is of great significance to the controlled generation of double emulsion droplets. A flow-focusing structure is used to realize the periodic dripping in coaxial capillary device. High-speed photography experiments are applied to explore the effects of the periodic generation of the inner droplets on the breakup modes of the compound jets and the results of droplets generation in the device. The results show that with the increase of the flow of the middle phase and the inner phase, the generation of the inner droplets presents periodic characteristics. The shape parameters in the process of inner droplet generation are extracted to derive the experimental critical condition of periodic dripping, and the prediction data and experimental results have obtained a good match. Through the coupling effect between the two layers of interface, the periodicity of the inner droplets makes the compound jets to present six kinds of breakup modes and the sequence of the droplets. In addition, the breakup of the middle phase fluid bridge is affected by the inner droplets through the types of Pinch-off in front of a droplet (PFD) and Pinch-off behind a droplet (PBD), both of which could be controlled by adjusting the flow rate of the middle phase. The results could provide a quantitative and economic way for biochemistry applications such as multi-stage drug release, capsule component dilution and multi-volume digital PCR.