Study On Droplet Actuation By Liquid Dielectrophoresis On Digital Microfluidic Platform

Digital microfluidics is a kind of technology that permits manipulation of nanoliter to microliter size droplets.With the advantages of less reagent consumption,rapid reaction and high integration,digital microfluidics has a good application value in biology,chemistry,medicine and other fields.In recent years,the manipulation of water droplet are easy to demonstrated on digital microfluidic chips,but oil droplet is difficult to manipulate due to the high-driving voltage.It limits the application of digital microfluidic.In this thesis,the principle of the droplet manipulation is explored,an electromechanical model for the electrowetting based microdroplet driving device,the actuation force for the parallel-plate device was derived.Based on the force calculation,the effects of droplet conductivity,dielectric constant,and the electric field frequencies on the electrical force exerted on the liquid droplet are studied.According to the electromechanical model,a low-voltage droplet manipulation scheme based on negative DEP effect is proposed.The droplet actuating platform is built,and four basic operations of droplet under 100 V voltage are successfully realized by using low-voltage droplet manipulation scheme.The movement rate of oil droplets in surfactant solutions of different kinds and concentrations under different frequency voltage is studied,and the effect of ion concentration on the movement rate is studied.The results show that the movement rate of oil drops increases with the increase of voltage frequency,under the same conditions,the movement rate of oil droplets is inversely proportional to the ion concentration of the solution.In order to explain the difference between the conclusion and the theory of the electromechanical model,the experiments of water droplets by common method are carried out.The movement rate of surfactant solutions with different kinds and concentrations under different frequency voltage is studied.The experimental results show that the driving rate of other droplets increases first and then tends to be stable with the increase of voltage frequency,except for the Silwet L-77 solution with concentration of 0.00125%(wt%),The possible causes of this phenomenon are discussed.The reasons for these phenomena may be related to the reversal of the dipole inside the liquid under low voltage.According to the low-voltage droplet manipulation scheme,a digital microfluidic chip is designed for the generation of on-chip double emulsion droplet,and the experiment of double emulsion droplet generation is carried out.The operation of water droplet and oil droplet is realized on a chip,and the oil drop and water drop with "tether" are successfully matched.It lays a foundation for the low pressure operation and application of the encapsulated droplets.