Research On Multi-scale Splitting Of Droplet Based On Conical Microstructure

The droplet microfluidic system has the unique advantages of miniaturization,compartmentalization,parallelization,etc.It is an important branch of the microfluidics research,and its basic operations include the fusion,splitting and screening of droplets.Droplet splitting can increase the yield of droplets,enhance the operability and flexibility of droplets,and has important research value.In the traditional rectangular channel section,T-type or Y-type split structure,the main splitting is the "plunger flow" droplet with the largest length larger than the channel width,while it is difficult to effectively control the splitting of smaller "spherical" droplets.Therefore,we designed a conical microchannel structure through the combination of the capillary glass tube and the PDMS channel to achieve efficient multi-scale splitting of "spherical" droplets.Firstly,the mechanism of droplet splitting in conical microstructures is analyzed.The theory of droplet dynamics in microchannels and the traditional theory of droplet splitting are expounded.The three-dimensional simulation model of droplet splitting in conical microchannels is established.The process of droplet splitting is simulated and analyzed by numerical simulation method.The mechanism of droplet splitting is analyzed based on the simulation of spatial flow field distribution in microchannels.Secondly,the volume-flow ratio of the cross section of the outlet channel is determined as the main fluid parameter affecting the splitting of droplets in the conical microstructures.The diameter ratio and volume ratio of the droplets after splitting are characterized as a phenomenon of the splitting volume distribution of droplets.The effects of different flow ratios,the depth of the conical tube into the main channel,the diameter of the conical orifice,the initial size of the droplet,and other fluid and structural parameters on the droplet splitting behavior were analyzed by simulation,which can provide guidance for further experimental research.Thirdly,based on the simulation results,we designed and fabricated a capillary glass tube-PDMS microfluidic chip with conical microstructure channel.With this chip as the core,we built an experimental platform for droplet high proportion splitting,and verified the process and mechanism of droplet splitting.The splitting of droplets in a conical microstructure can be divided into three stages: droplet contact,sub-droplet growth and sub-droplet detachment,and the splitting behavior is mainly caused by the high capillary number region near the conical orifice.Finally,the influence parameters of droplet splitting in conical structure were analyzed by experiments,and the effects of different outlet flow ratio,capillary penetration depth and capillary orifice diameter on droplet volume distribution were verified,which provided experimental data support for further research and engineering application of droplet splitting with fixed proportion.