Droplet generation by induced electric field between charged surface and dielectric material

Abstract

The dispensing of tiny droplets is a basic and crucial process in a myriad of applications, such as DNA/protein microarray, cell cultures, chemical synthesis of microparticles, and digital microfluidics. Therefore, many methods for droplet generation is proposed such as inkjet jetting, piezo-electric jetting, thermal jetting, and electrohydrodynamic(EHD) jetting. The deformation of charged surface by electric field during dispensing process in EHD jetting resulted in the creation of much smaller droplets than the nozzle unlike other printing methods. As one of the EHD jetting method, electric charge concentration (ECC) method is introduced to dispense the droplet by electric field between charged surface and target substrate. The fact that electric induction happens in both conductive and dielectric materials means that ECC method can apply to those materials. First, the ECC experiment in this study was conducted by limiting the target material with a dielectric material, since the electric induction mechanism depends on the substrate characteristics. It is believed that the ECC method can be an alternative to the currently used droplet dispensing method, because dielectric materials work as target substrate where the droplet is dispensed in various applications such as micro-channel or printed electronics. In chapter II, the demonstration of dispensing droplet by ECC method is applied on both solid and fluid, which are dielectric material. The dispensing regime of ECC method to dispense the droplet into oil is examined, and the size of droplet dispensed is experimentally measured. The effect of ground electrode is examined experimentally with the glass, and the demonstration of dispensing oil droplet onto the solid is successfully fulfilled. In chapter III, the applicability of ECC dispensing method to practical applications is demonstrated. Finally, in the chapter IV, numerical simulation is fulfilled to interpret the ECC dispensing phenomenon.