(162s) The Motion of a Conducting Droplet in Dielectric Fluid under the Electric Field

The research field of an electrically charged droplet is wide, encompassing various branches from electrohydrodynamics to colloidal and interface phenomena. In the present work, electrical charging phenomenon of a conducting droplet in dielectric fluid on the electrode surface has been studied. At the moment a droplet touches the surface of the electrode, it is discharged the own charges into the electrode and get charged by the electrode. Then the droplet is repulsed from the electrode due to Coulombic force and is moved to the opposite electrode. The droplet, which approaches the opposite electrode, also shows a similar behavior. This process repeats itself. This is the so-called contact charging phenomenon. This phenomenon has two interesting parts. First is the deformation of the water droplet near electrode. Charges on the surface of the water droplet cause the shape deformation of the water droplet into the cusped shape due to the charge transfer from a droplet into the electrode. Second is the motion of a water droplet between two electrodes. Because the drop is in the steady state in the middle region, the electric charge on the water droplet can be determined from force balance between the columbic force and the drag force. Accordingly, the effects of the electric field, the bulk viscosity, and the droplet size in this phenomenon were investigated. The drag force of a liquid droplet is assumed to be governed by Hadarmard-Rybczynski solution. The experimental observations of the motion of the water droplet using the high speed CCD camera are used to the calculation of an electrical charge and to capture the droplet deformation near the electrode. It is shown that the more electrical charging occurs with larger drop size and higher electric field. The effect of the bulk viscosity is more complicated. In the case of not so high viscosity, the amount of charge increases with the bulk viscosity. However, in the very high viscosity case, the trend may be reversed. The framework is outlined to describe the dynamics of a charged droplet in dielectric fluid under the electric field.

Key word: electric charge, water droplet, deformation, electric field