Control Methods And Experimental Research Of Droplet’s Moving Into Parallel-plates Structure

With the advantages of less consume of sample, higher analysis efficiency and easier of integration, microfluidic systems especially Digital Microfluidics(DMF) systems have got a very wide application in the field of chemical analysis and biomedical. There are two main tapes of DMF. The one is closed system(parallel-plate) and the other is open system(single-plate). Because each structure has its own ability, so a system combining both closed and open systems on a chip comes out. Droplet should be able to move back and forth between these two structures, but to the big droplets, it is so difficult to moving into parallelplate structure with a narrow gap. For the purpose of moving the droplet into the gap in a spontaneous way we improve the structure of upper plate and propose a new way of driving the droplets.First, this dissertation analyzed the factors which effect the process of droplet’s moving into the gap. The whole process was divided into two parts which were named spontaneous moving and pressure moving respectively. Based on the Molecular dynamics theory and the simulation made by COMSOL Multiphysics, this dissertation concluded that the spontaneous moving was effected by either the thickness, the wettability and the shape of upper plate or the width of the gap. Based on this conclusion, this dissertation optimized the shape and the thickness of upper plate. Besides that, combined with the model of the droplet’s moving in unparalleled plates’ structure, we propose a scheme which pushing droplet into parallel-plate structure by moving the upper plate up and down.Second, a simulation about the process of droplet’s moving into the gap has been made. First, a procedure about microdroplet based on the library function OPENGL and Smoothed Particle Hydrodynamics Method(SPH) has been written. A simulation about the droplet’s forming on a plate and moving into the gap was achieved. We analyzed each parameter during this moving in detail. The procedure was verified by comparing the simulation results of the forming of droplet and our common sense. By comparing the moving situations with different widths of gap and different shapes of upper plate, the effect made by the width of gap and the shape of upper plate was verified.At last, the verification experiments has been carried out. First the hydrophobic surface which covered by Teflon was taken as the platform of moving droplet. The theory and simulation of the factors about droplet’s spontaneous moving was verified by comparing the different situations of droplet’s spontaneous moving with different widths of gap. After setting up the controlling machine, the upper plate’s up and down were achieved. After that, the big droplet, even larger than 10μL, was moved into the gap of parallel-plates. At last, we even popularized this scheme to the hydrophilic surface.This dissertation analyzed the moving process of droplet into parallel-plates structure and optimized this moving, laid the foundation for the further research of droplet’s moving.