Emulsified products such as cosmetics and milk have become indispensable products in people's daily lives, while traditional processes such as stirring, heating or adding special surfactants often produce polydisperse emulsions. Therefore, how to effectively obtain emulsions with good monodispersity is an important problem that needs to be solved in colloid science. The microfluidic emulsification system generates a series of microliter to nanoliter microdroplets with controllable size and good monodispersity on the chip by controlling the flow rate. The microdroplets generated on the microfluidic chip have good consistency in size and shape, which is not only easy to manipulate, but also has good monodispersity.
 

　　The system can be controlled to provide a flexible and reliable technology for generating monodisperse double emulsion droplets. Micron-sized emulsion droplets can be produced, which contain smaller droplets inside, with high control reproducibility and selectable outer and inner droplet sizes. Important applications include: drug delivery and enzyme immobilization, food taste masking, cosmetic key delivery carriers, in vitro coating, flow cytometry and microencapsulation carriers.
 

　　Double emulsion droplets are very promising materials for the cosmetic, pharmaceutical or food industries. Double emulsion droplets can be used to encapsulate relatively sensitive compounds (drugs, vitamins, fragrances...), protect the active substances and release the encapsulated compounds at the right time and place as required.
 

　　The acquisition of double emulsion droplets is very complicated. Double emulsion droplets can be stably generated with the help of microfluidics technology. Currently, the commonly used structures for generating droplets are the following three: co-flow, T-junction, and flow focus. All three structures can be used to form double emulsion droplets. The simpler geometric shape for generating double emulsion droplets is two consecutive flow focusing structures. The droplets formed at one flow focus are encapsulated into the outer droplets at the next flow focus.
 

　　Typically, double emulsions are prepared in two steps using a dispersed phase containing two surfactants of different properties. For example, to form a water-in-oil-in-water emulsion, water is first emulsified with an oil phase containing a hydrophobic surfactant and then re-emulsified with an aqueous phase containing a hydrophilic surfactant. Double emulsion droplets can be effectively generated using glass capillaries, but they are difficult to assemble and have poor reproducibility. A more stable and reliable method is to use a locally modified microfluidic chip. Using a microfluidic emulsification system and a locally modified double emulsion droplet generation chip and corresponding fixture, users can complete the generation of double emulsion droplets in less than five minutes by simply connecting the pipeline.