Effect Of Collecting Channels On Droplet Generation In Glass Capillary Microfluidic Devices

Generation of highly monodisperse droplets has unique advantages in the fields of chemistry,food,medicine,biology and so on.Droplet microfluidic technology can accurately control the generation of droplets by adjusting the flow rate of the fluid and it provides a new method for the preparation of droplets with uniform particle size distribution.So the technology has been widely used in recent years.The glass capillary microfluidic chip assembled by coaxial glass capillary is one of the mainstream microfluidic devices.It has three-dimensional axisymmetric channel and the inner phase can be totally embraced by the outer phase.Thus,the effects of channel wall wettability on the droplet formation can be ignored and more uniform and higher flux droplets can be produced.However,the collecting tube is only prepared by experience at present,and few studies have been conducted.In this paper,the influence of the morphology of collecting channels on the droplet formation in glass capillary chips is studied in depth.The research work is of great significance for the preparation and application of droplet in capillary chips.Firstly,based on the basic theory of two-phase flow in microchannels,the two kinds of single-emulsion droplet generation model in coaxial flowing method in the glass capillary microfluidic chip,dripping and jetting,are analyzed.According to the force analysis of the droplet in the rupture process,droplet size formula is established and the parameters that affect the generation of droplets are analyzed.On the basis of single-emulsion droplet,the effect of fluid flow rate on the doubleemulsion droplets is studied.Secondly,based on the physical field coupling software,two-dimensional models of glass capillary chips with tapered collecting channels,concave collecting channels and parallel collecting channels are constructed respectively.Through numerical simulation,the influence trend of external fluid viscosity,surface tension coefficient,two-phase flow ratio and channel structure on the formation of droplets in the capillary chip is analyzed and compared with the theoretical analysis results,which provides guidance for the experimental study.Thirdly,glass capillary chips with three different types of collecting channels are fabricated and the experimental system is established.The effect of continuous phase flow rate on the formation of single emulsion droplets in the chip is verified by experiments.The droplet in the tapered collecting channel is basically consistent with the theoretical analysis.In addition,the formulas for predicting droplet size in the other two chip shapes are fitted and the droplet size can be predicted well.Finally,glass capillary chips used to produce the double-emulsion droplets are fabricated.The influence of the three-phase fluid flow rate on the double emulsion droplet shell,inner core size and number of inner cores in different collecting channels is experimentally analyzed.And the relationship between them is deduced according to the law of conservation of mass to verify the experimental results.The distribution of the number of double-emulsion droplet cores under different fluid flow rates is experimentally studied.