Simulation And Experiment Of Droplet Ejection Based On A Hybrid Pneumatic Electrohydrodynamic Method

The droplet ejection is a new type of technology that has received extensive attention in recent years,and is mainly used to form micro droplets or apply a small amount of samples.Its main applications are 3D printing,microelectronic packaging,genetic engineering,and biomedical engineering.Traditional droplet ejection technologies include piezoelectric method,thermal bubble method,electrostatic method,pneumatic method,and electrohydrodynamic（EHD）method.In this paper we analyzed the main advantages and disadvantages of the pneumatic method and the EHD method.The advantages of the pneumatic method are that the drop-on-demand mode is more stable,and the disadvantage is that the droplet size is larger;the advantage of the EHD method is that the droplet size is smaller,and the disadvantage is that the drop-on-demand mode cannot be achieved.Therefore,a Hybrid Pneumatic-Electrohydrodynamic（HPEHD）ejection method is built,which combines the advantages of the above two methods and circumvents the disadvantages.A high-voltage electrostatic field is applied between the nozzle and the collection substrate.A small amount of liquid is squeezed out in the pneumatic process but not enough to form droplets,and the strong electric field stretches the squeezed liquid to break up to form droplets.Compared with the pneumatic method,the droplet diameter of the HPEHD method can be reduced by more than 50%,and the stability of the drop-on-demand mode is close to that of the pneumatic method.By the finite element analysis method COMSOL Multiphysics is used to build a model suitable for the pneumatic method,EHD method,and HPEHD method,whith is to study the basic properties of the three methods and to explore the feasibility of the HPEHD method.An ejection device suitable for HPEHD method is built in the laboratory.Its basic structure is improved by installing electrodes on the pneumatic ejection device.Machine vision is used to observe the stability of the ejection process and measure droplet size.We verified the feasibility and advantages of the HPEHD method,observed the droplet ejection process and verified its ejection mechanism.The three main conditions that affect the HPEHD ejection are the gas source pressure P₀,the solenoid valve opening timeΔt,and the electrostatic voltage V₀.The increase in gas source pressure P₀ and solenoid valve opening timeΔt will increase the droplet size within a considerable range,and the electrostatic voltage V₀ has little effect on the size of droplets.Finally,bioink ejection is achieved by HPEHD method.HPEHD method has little effect on cell viability,and the cell survival rate is 98.7%,which proves that it has certain application prospects in the field of biomedicine engineering.