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.

中文翻译：

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周期性内部滴落对毛细管装置中复合射流的作用

摘要 双乳化液滴在医药、化工、能源等领域具有巨大的潜在应用价值。了解复合射流破碎过程中两层界面的耦合行为对于双乳液液滴的可控生成具有重要意义。同轴毛细管装置采用聚流结构实现周期性滴液。应用高速摄影实验来探索内部液滴的周期性产生对复合射流破碎模式的影响以及装置中液滴产生的结果。结果表明，随着中间相和内相流量的增加，内层液滴的生成呈现周期性特征。提取内部液滴生成过程中的形状参数，推导出周期性滴落的实验临界条件，预测数据与实验结果得到了较好的匹配。通过两层界面之间的耦合作用，内部液滴的周期性使复合射流呈现出六种破碎模式和液滴的顺序。此外，中间相流体桥的破裂通过液滴前夹断（PFD）和液滴后夹断（PBD）类型受到内部液滴的影响，两者都可以通过以下方式控制调节中间相的流速。结果可以为生物化学应用提供定量和经济的方法，例如多阶段药物释放，