| Liquid metal is a kind of liquid at room temperature,with both metal and fluid characteristics,such as,good electrical conductivity,thermal conductivity,excellent fluidity and flexibility.Due to its unique physical and chemical characteristics,liquid metals have been widely used in thermal management of high-power density electronic devices,nuclear reactors,etc.In recent years,they have also been successfully applied in flexible electronic devices,intelligent actuators,electrochemical sensors,micro-electromechanical systems and other relative fields.Liquid metal microspheres with independent three-dimensional symmetric structure have attracted much attention in periodic advanced functional devices.However,due to its high surface tension and high density,how to split large liquid metal into homogeneous micro-scale microspheres has become an urgent problem needed to be solved.Meanwhile,liquid metal has excellent electrodynamic characteristics under the action of electric field,which has the potential to be utilized in fluid driving and fluid mixing when energized by electric field.It is expected to make breakthroughs in biological driving.Therefore,we take gallium indium tin alloy Galinstan liquid metal as the research object to investigate the production of liquid metal droplet at micro scale and the electrodynamic characteristics of liquid metal surface under the action of electric field.Based on the basic theory of micro-nano two-phase flow,the Plateau-Rayleigh instability model in the formation and droplet process was analyzed.A micro-needle induced approach was adopted to produced liquid metal microdroplets on the co-flowing capillary microfluidics.We established the Plateau-Rayleigh instability model for the inhibition of stickiness induced by micro-needle.A two-phase flow axisymmetric numerical model for liquid metal droplet formation induced by micro-needle induced was built based on phase field method and analyzed the formation process of liquid metal droplet.The effects of wettability,interfacial tension,external viscosity and internal and external fluid velocity on the diameter and production frequency of liquid metal microspheres were investigated,which laid a theoretical foundation for the preparation of microspheres wi th high surface tension.Based on the interface theory,electrochemical polarization process and electrodynamics theory,we established the electric double layer charging dynamics model for liquid metal/electrolyte,revealed the continuous electrowetting mechanism.Then we established the mathematical model of pressure drop on neighboring side of the liquid metal droplet surface,which provided the reference for investigating the droplet deformation and the resulted fluid flow around the conducting droplet.Based on the micro-needle induced viscous effect analysis,the co-flowing capillary microfluidic chip sysytem with micro-needle induced strategy for liquid metal microspheres was established.we experimentally investigated the liquid metal generation process and the shearing mechanical behavior of the droplet when the droplet was detached from the capillary tip.we comparatively analyzed liquid metal droplets uniformity between the traditionally co-flowing capillary microfuidics and the micro-needle induced approach,and analyzed the stability enhancement for micro-needle entrainment on the liquid metal droplet generation process.The influence of wall wettability on the droplet size distribution of liquid metal was studied by inserting the metallic micro-needles and glass capillary inside the inner phase glass capillary.The effects of the interfacial tension between two phase fluids,the ratio of the fluid velocity of internal and external phases on the liquid metal microspheres diameter were investigated.By adjusting the flow velocity of neighboring phases fluids,different sizes of liquid metal microspheres could be efficiently prepared,and the minimum diameter of droplet with 65 ?m could be obtained.Under the applied direct current(DC)bias electric field,the surface tension on both sides of the liquid metal slug could be adjusted due to the difference of electric potential,inducing the continuous electrowetting effect.Based on the the electric field regulating surface tension of liquid metal droplet,a liquid metal based motor was proposed based on the electro-induced surface tension driving mechanism.The experimental system for liquid metal enabled pump was establised to obtain the average velocity of liquid metal segment moving in micro-channel under the action of electric field.The influences of electrolyte concentration,voltage amplitude,driving electric field frequency and liquid metal droplet volume on the driving speed of the pump were studied experimentally.The oscillation and forward lo comotion while oscillating behaviors of the liquid metal under low frequency are studied,which provided the basis for the application of liquid metal in liquid motor with low power consumption and no wear.According to the theories of electric double layer,the induced charge electric osmosis and continuous electrowetting mechanism,we established the liquid metal/electrolyte interface electric double layer charging dynamics model when the alternating current(AC)was applied.The pressure drop for the ele ctric double layer caused simultaneously by the surface free charges of the charged droplet and the induced electric charges.We obtained the flow pattern induced by the the global viscous shear stress and the local viscous shear component.The fluid flow around the liquid metal droplet numerical model was established,and the influence of voltage magnitude and the driving frequency of AC electric field on continuous electric wetting effect were investigated.The pumping velocity and fluid velocity under the action of AC electrowetting were explored,which laid a theoretical foundation for fluid pumping and mixing.In addition,a high-throughput fluid micro-mixer was designed based on the chaotic advection surrounding the droplet surface caused by liquid metal deformation under the action of AC electric field,and the influence voltage amplitude,field frequency,electrolyte ion concentrations and inlet velocities on fluid mixing performance were explored.The mixing efficiency of the proposed micro-mixer was reach up to 91%.The electric properties of the conductive droplet regulated by electric field could provide theoretical value for its application in microfluidic. |
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