T型微通道中液滴半阻塞不对称分裂行为研究

液滴不对称分裂是获得不同尺寸微液滴的优选方法,研究液滴不对称分裂行为对于生物医学、能源化工及食品工程等领域具有重要意义.本文研制T型微通道芯片并设计搭建T型微通道液滴半阻塞不对称分裂行为可视化实验平台,研究流量调控对微液滴分裂比的影响规律,并建立理论模型对分裂比进行预测,得到以下结论:液滴不对称挤压分裂过程分为挤压前期、挤压后期和快速夹断阶段,在挤压前期,液滴颈部宽度随时间呈线性变化,在挤压后期,颈部宽度随时间呈指数关系,而在快速夹断阶段,液滴颈部向心收缩的界面附加压力占主导,液滴颈部宽度剧烈收缩,呈断崖式减小;调控分支通道流量可对液滴不对称分裂比进行调控,且调控作用受毛细数影响较大;基于液液流动压降模型的液滴分裂比预测模型能够有效预测液滴分裂比.

Semi-obstructed splitting behaviors of droplet in an asymmetric microfluidic T-junction

Asymmetric droplet splitting is a common method to obtain micro-droplets of different sizes.The study of droplet asymmetric splitting behaviors is of great significance to the fields of biomedicine,energy,chemical industry and food engineering.In this paper,the control flow is introduced into a branch of the T-shaped microchannel to control the pressure distribution in the channel and precisely control the size of the daughter droplets.The method is simple to operate and is a preferred method for asymmetric microfluidic splitting.Existing studies have analyzed droplet splitting modes,critical conditions for flow pattern transitions,and splitting dynamics,but the theoretical prediction of droplet asymmetric splitting behaviors needs to be strengthened.Moreover,compared with tunnel splitting and obstructed splitting,which are more abundantly studied,neither semi-obstructed splitting as an intermediate state of tunnel splitting nor obstructed splitting is analyzed sufficiently.Therefore,a microfluidic T-junction chip is designed and fabricated,with which asymmetrical splitting behaviors of droplets with a tunnel in a microfluidic T-junction are investigated experimentally.The influence of flow rate regulation on the droplet splitting ratio is studied.And a theoretical model is also established to predict the splitting ratio.The results are concluded as follows:1)the process of asymmetrical droplet splitting is divided into three stages i.e.early squeezing,late squeezing and rapid pinch-off stage.In the early stage of squeezing,the radius of curvature of the droplet neck is sizable,and the additional pressure of interfacial tension is minor.Compared with the additional pressure that hinders neck contraction,the upstream continuous phase driving force is dominant,and the width of the neck changes linearly with time;in the process of late squeezing,the upstream pressure driving effect is still greater than the hindering effect of the additional tension,and the neck width changes exponentially with time;However,in the rapid pinch-off stage,the interfacial tension pointing to the center of the cross section of droplet neck dominates the pinch-off stage.Then,the droplet neck shrinks sharply.2)Adjusting the flow rate of the branch channel can effectively control the asymmetric splitting ratio of the droplets,and under the current semi-obstructed asymmetric splitting of the droplets,the regulation effect is less affected by the size of the mother droplet,but more affected by the capillary number.3)The prediction model of droplet splitting ratio based on the pressure drop model can effectively predict the droplet splitting ratio.