Research On Microdroplet Drive Based On Dielectric Effect

Dielectric effect is an important droplet driving technology in microfluidics.It is caused by a non-uniform electric field to generate a polarized dipole moment,and the droplet is subjected to deformation or movement by the dielectric power.Due to the strong manipulating ability of microdroplets,the dielectric effect is not only prominent in digital microfluidics,but also favored by researchers in liquid lens.As a typical representative of microfluidic optics,the zoom liquid lens uses liquid as an optical medium,and uses microfluidic technology to control the shape of the liquid-liquid or liquid-vapor interface to achieve automatic zooming.Liquid lens has the advantages of fast response,compact structure,low cost,low power consumption and easy integration.It has broad application prospects in the fields of portable camera,imaging technology and medical endoscope.However,the existing liquid lens mostly use conductive liquid and direct pressurization to achieve focal length regulation,which generally have the disadvantages of poor thermal stability,narrow operating temperature range,and high driving voltage.This article describes a miniature dielectric liquid lens.The principle is that the droplets are subjected to dielectric power to change shape and change in motion state,and the dielectric power is due to an uneven electric field.The research content of this paper mainly includes the following aspects:(1)In view of the problems of bubbles,temperature limitation and evaporation caused by electrolysis in the conductive salt solution commonly used in liquid lenses in the past,this paper uses a more stable transparent dielectric liquid to replace the conductive solution?The dielectric liquid itself is non-conductive or non-conductor,which can avoid electrolytic breakdown during the driving process.Moreover,the dielectric liquid can be selected in a wider range and more stable in nature.The dielectric power generated by the non-uniform electric field enhances and controls the wettability of the dielectric liquid to achieve the effect of manipulating the droplet deformation and displacement.At the same time,the experiment compared the driving effects of the common four dielectric liquids.(2)The experimental research on the influencing factors of micro-droplet driving based on dielectric effect was carried out.The effects of electrode pattern,dielectric layer thickness and dielectric droplets on the driving effect were discussed by experiments,and the optimal parameter combination was determined.Electrode shape is a necessary condition for generating uneven electric field.In this paper,staggered structure and interdigital electrode are designed for lateral diffusion and circular diffusion of droplets respectively,and they are applied to discretized droplet drive and liquid lens.expected result.The 5 ?m thick PDMS film prepared by the spin coating method has the dual function of the dielectric layer and the hydrophobic layer,which can increase the initial contact angle and facilitate the change of the droplet shape.(3)In view of the driving method of direct pressurization in the past,the innovative improvement of this paper is the method of frequency modulation and pressurization,so that the initial driving voltage of the droplet is greatly reduced.This method is the driving effect of voltage and frequency acting on the droplet at the same time,which is further affected by the influence of the single research voltage on the driving effect.At the same time,simple external circuits are also easy to integrate and miniaturize.On this basis,the digital droplet control chip involved in droplet transport,splitting,merging and other manipulations.(4)Compared with the common liquid lens driving method and its mechanical structure,a dielectric liquid lens based on frequency modulation method is designed and fabricated.The organic material is packaged into a classic circular structure,and the focal length and imaging quality of the dielectric effect liquid zoom lens are studied according to the geometric optics theory.Experiments verify the interaction between applied frequency and voltage amplitude,frequency and contact angle,frequency and focal length,and aperture.The dielectric effect liquid lens has the advantages of small size,good recovery and zoom effect.The zoom distance is 6~8cm,the response time is about 375 ms,and the power consumption is about 17.7mW.