| Microfluidics and Nanofluidics have been studied for several decades.We are now proceeding into digital Microfluidics,which shows a prosperous future and huge potential for application,after the first generation of continuous Microfluidics and Nanofluidics.The micro-droplet preparation technology is the core of Microfluidics,due to the micro-droplet has being the basic target for manipulation in all of the technology.Thus,the quality of Micro-droplets preparation largely determines the quality of whole microfluidics system and the field of application.In a word,the droplet preparation has become the most important process and the basis of digital Micro-fluidics.In general,the size range of droplet situated around 0?m to 1000?m,moreover,the monodispersity of droplets is a more important qualification for the application.For example,the highly monodispersed droplets will be qualified into fields like drug test,bio-chemical,and chemistry.Normally,there are two kinds of methods for droplet preparation according to it principal.One is based on the inertial force of the continuous phase with high-throughput,including T-conjunction,cross focusing and shell flow;another one is based on the Laplace pressure of dispersing phase with high monodispersity of droplets,like the step emulsification.Step emulsification is proposed recently,which has high stability and monodispersity of emulsification even in a long time production.Moreover,it is impervious to flow change,which is a critical feature for monodispersity.While the vibration from pump and environment will might surpass the impervious range and causes size change among droplets,which breaks the monodispersity of droplet.Therefore,this research taking into the effect from surface tension and flow variation,propose a kind of device that utilizing electro-wetting technology to reduce the negative effect caused from flow fluctuation.The device is able to apply on fields which demand high droplet monodispersity.The workload of this study includes what listed below:1.Design and fabricate a microfluidics step chip with a contact angle control function: selecting materials for each layer of the electro-wetting step;try to understand the best process of PI coating for insolation layer;explain what the effect of electro-wetting may bring to the contact angle on the dielectric when immersed in air and silicon oil;fabricate a step for droplet creating which combining electrowetting technology to control the contact angle;measure and explain the impact brought from electro-wetting on the monodispersity of droplets;observe the critical phenomena of emulsification.2.simulate the step emulsification with VOF method to chase the phase which verifies the four process of emulsification in experiments.Expand the relation between surface tension and flow rate figure and explain the reason why the size of droplet varies with the flow rate and surface tension with the velocity map and pressure map.3.design and fabricate an automatic control system to decrease the reduction of monodispersity caused by flow rate fluctuation and vibration;design a flow rate sensor based on a pressure sensor;explore the method to utilize the electro-wetting technology to decrease the negative influence caused by flow rate change;coding the STM32 system to realize the goal.This study proposes a practical design of device which combines both electrowetting and step emulsification technology and assembly a control system to decrease the negative influence from flow rate pulse.It is useful to apply this device on long period and continuous droplet production where has high demand on droplet monodispersity. |
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