Droplet Self-actuation Principle And Control Method In Asymmetric Structure

Droplet based microfluidic technology is a new technology to realize the independent operation of microliter or sodium upgrade droplet.It has the advantages of less sample consumption,fast reaction speed and strong operability,and has been widely used in various biochemical experiments.Droplet self-actuation technology,as a common droplet microfluidic technology,realizes the actuation of tiny droplet by controlling the properties of the structure surface.Generally,there are two methods:one is to build wetting gradient on the surface through surface processing technology from the micro level,so as to generate wetting force to drive droplets;The second is from the macro point of view,by building an asymmetric structure(such as nonparallel plate structure)on the whole,thus producing an asymmetric surface tension to drive the droplet.In the existing studies,these two methods can only realize one-way droplet drive,which greatly limits the application of droplet self-drive.Therefore,how to find away to realize the bidirectional controlled operation of droplet and realize the controlled operation of droplet with this method is of vital importance.In order to realize the controllable operation of liquid droplets,this paper has carried out an in-depth study of two kinds of related operations layer by layer:first,the bidirectional controllable operation of liquid droplets in an asymmetric structure(that is,the bidirectional movement operation of liquid droplets in nonparallel plate structure);Secondly,the operation of droplet in and out of asymmetric structure is studied(that is,the transfer operation of droplet in open single-plate structure and closed double-plate structure).Firstly,by using these two principles,the self-actuating conditions of droplets in the structure of the nonparallel plates are analyzed,especially the self-actuating conditions of droplets in the hydrophobic unparallel plates are analyzed.Then,we analyzed and simulated the droplet's self-drive(liquid bridge formation process)in the single and parallel plates integrated structure,and obtained the model of liquid bridge formation and the influence of various parameters on the process.Secondly,we study the ratchet-like strategy.Firstly,we put forward an analysis method of droplet ratchet-like strategy based on "chord" method,and obtained a general conclusion that "the change rate of contact angle can be expressed explicitly by the change rate of chord length".After analysis method based on the chord length,we respectively analyzed the droplets in the nonparallel plate structure and single and single-parallel integrated structure driven by ratchet-like strategy,we found that the contact angle change rate throughout the asymmetry in the process is the root cause of this kind of drive can be successfully implemented,in order to verify this conclusion,we respectively through the simulation of two models are simulated,the results are in complete accord with theory.At last,the influence factors of self-actuating efficiency of the ratchet-like strategy are studied.Then,we combine the analysis of self-actuation in chapter 2 and the analysis of ratchet-like strategy in chapter 3,we apply it to drip-actuation control and complete the control optimization.The material parameters and control parameters in the nonparallel plate structures are analyzed and optimized.For the case of single-parallel integrated structure,we studied the influence of material parameters and control parameters and upper plate thickness on the motion efficiency,and obtained its optimal control scheme.Finally,the droplet driving simulation of the nonparallel plate structure and the single-parallel integrated structure is carried out to verify the feasibility of the optimization scheme in this paper.Finally,based on the above theoretical analysis,the droplet driven experiment under asymmetric structure is carried out.First of all,the influence of various parameters on self-actuation and opening and closing auxiliary actuation is verified from the experimental point of view for the single-plate and double-plate transition zone structure.After that,a special liquid drop tweezers was proposed based on the thin plate and the structure of hydrophobic non-parallel plate to realize the capture and release of liquid drops on various hydrophobic surface.The liquid drops on the hydrophobic surface(120° contact Angle)were successfully transferred to the superhydrophobic surface(150° contact Angle).Based on the above method,an integrated droplet tweezers were designed to simplify droplet capture and release process.The microdroplets containing zebra eggs and zebrafish larvae were successfully transferred without loss based on the forceps.Compared with other droplet transfer methods,this method has a low cost(less than 5 yuan),does not need external stimulation to ensure biological activity,and is easy to carry and manufacture(small size,not easy to damage).Therefore,it has a good application prospect.The principle and application of droplet self-drive and ratchet assisted drive are discussed in this paper.The theories,methods and conclusions used in this paper have certain enlightenment and guiding significance for further research and design of droplet based microfluidic technology.