Loading a High-Viscous Droplet via the Cone-Shaped Liquid Bridge Induced by an Electrostatic Force

Working Regime Criteria for Microscale Electrohydrodynamic Conduction Pumps

We investigated the microscale electrohydrodynamic (EHD) conduction pumps in a wide range of working regimes, from the saturation regime to the ohmic regime. We showed that the existing macro- and microscale theoretical models could not accurately predict the electric force of microscale EHD conduction pumps, especially for the cases of a strong diffusion effect. We clarified that the failure is caused by a rough estimate of the heterocharge layer thickness. We revised the expression of heterocharge layer thickness by considering the diffusion effect and developed a new theoretical model for the microscale EHD conduction pumps based on the revised expression of heterocharge layer thickness. The results showed that our model can accurately predict the dimensionless electric force of the microscale EHD conduction pumps even for the cases of a strong diffusion effect. Furthermore, we developed a working regime map of microscale EHD conduction pumps and found that the microscale EHD conduction pumps more easily fall into the saturation regime compared with the macroscale EHD conduction pumps due to the enhanced diffusion effect; in other words, the microscale EHD conduction pumps have a wider saturation regime. We showed that the conduction number C0 could not distinguish the working regime of the microscale EHD conduction pumps because it does not take the diffusion effect into account. By employing the revised expression of heterocharge layer thickness, we proposed a new dimensionless number, C0D to distinguish the working regimes of microscale EHD conduction pumps.

Study on the Formation and Controllable Movement of Polymer Liquid Columns Based on Dynamic Control of Spatial Electric Field Distribution

Liquid deformation and motion are very common natural phenomena and of great value in various practical applications. In this study, a dielectric fluid column formation and directional flow phenomenon are presented. Dielectric fluid can grow upward to form a liquid column through a spatial electric field and realize directional and controllable operation of the liquid column by regulating spatial electric field distribution. First, the adjustable electric field space is constructed by connecting the two parallel electrodes to the high-voltage DC power supply. Then, the regional electric field distribution was adjusted by the upper plate graphic and power supply regulation to drive the polymer liquid on the lower plate electrode to form a liquid column at different positions. The results show that the polymer liquid column can be driven by the spatial electric field distributed dynamic control method and that the height and the narrowest width of the liquid column are directly controlled by the voltage. With the experiment conditions that the distance between two parallel electrodes is 5-15 mm, the formation of liquid columns with a height of 5-15 mm can be controlled. In addition, the liquid column can be driven by adjusting the on-states of different conductive regions. When the voltage is 10 kV, the liquid column directional movement speed can reach 1 mm/s. The higher the voltage, the faster the directional movement. The research results can be used as producing polydimethylsiloxane stamp, localized heating and temperature control, fabricating a pulsating heat pipe, and so on.

Polarization Effect and Improvement of the Electroinduced Formation Efficiency of a Highly Viscous Liquid Bridge

In the electroinduced formation of a highly viscous liquid bridge, improving the efficiency of formation is important for industrial applications. This paper presents the preregulation method of the polarization status to shorten the formation time of a liquid bridge. The hindering effect of high viscosity on the polarization of liquid suspensions was investigated. The formation time of the liquid bridge is shortened, and stability is improved by prepolarizing the initial liquid film, with a maximum reduction in the average and standard deviation of times by 12.65 and 2.52 s, respectively. These effects are confirmed at different viscosities and voltages. In addition, this method has no obvious influence on the shape of the liquid bridge. This study provides an approach to improve the electroinduced formation.

Stretching breakup of a conical liquid bridge with a moving contact line

The stretching breakup of a conical liquid bridge is the core process of micro-dispensing. To precisely control the droplet loading and improve the dispensing resolution, a detailed study of bridge breakup with a moving contact line is required. A conical liquid bridge is established by an electric field and stretching breakup is investigated here. The effect of contact line state is investigated by examining the pressure at the symmetry axis. Compared to the pinned case, the moving contact line causes a shift of the pressure maximum from the bridge neck to top, and it facilitates the evacuation of the bridge top. For the moving case, factors affecting the contact line motion are then considered. The results show that the increase of the stretching velocity U and the decrease of the initial top radius R _top accelerate the contact line motion. And the amount of contact line movement is basically constant. To analyze the influence of the moving contact line on bridge breakup, neck evolution is tracked under different U. An increase of U decreases the breakup time and increases the breakup position. Based on the breakup position and the remnant radius, the influences of U and R _top on remnant volume V _d are examined. It is found that V _d decreases with an increase of U and increases with an increase of R _top. Accordingly, different sizes of remnant volume can be obtained by adjusting U and R _top. This is helpful for the optimization of liquid loading for transfer printing.

Parallel Microdispensing Method of High-Viscous Liquid Based on Electrostatic Force

Parallel microdispensing of high-viscous liquid is a fundamental task in many industrial processes. Herein, a smart printing head is developed, including the probe array, the electric control module, the contact force measurement module, and the extra force balance module. The parallel dispensing of high-viscous liquid in nL level is achieved. The interacting effect between probes on the loading process is analyzed too. According to the result, the interacting effect between probes has a strong influence on the loading process. Therefore, the strategy of serial electrical loading and parallel transfer printing is utilized. Finally, the dependency of transfer printing volume on probe size, etc., is experimentally investigated. The volume of the loaded droplet can be controlled by the lifting velocity of the probe array, and the volume of the transferred droplet can be adjusted by the size of the probe instead of the contact force. The advantage of the proposed method is to realize the highly repeatable parallel dispensing of high-viscous liquid with a relatively simple device.