Electrostatic formation of liquid drop in pin-to-plate discharge system

A preliminary investigation was conducted on electrostatic formation of a liquid drop. High voltage was applied between an insulative capillary tube filled with water and a metal plate electrode. Formation of a water drop was observed at the dark discharge under conditions of appropriate voltage application and water level. Although the electrostatic attractive Coulomb force is small, in the order of 10 μN at the voltage lower than the corona onset, it is large enough to separate the water drop to the capillary tube against surface tension at certain conditions. The diameter of the drop was about one millimeter. At the beginning of corona discharge, however, water mist was dispersed at wide angle from the tip of the tube due to the Coulomb repulsive force of charged mist. When the applied voltage was further icreased, water mist became to be dispersed like spray, because the ionic wind prevented the separation and spread of the droplet. Application of adjusted pulse voltage can form a droplet of which formation is synchronized with the pulse. The diameter of the droplet depended on the applied voltage and the tube diameter. The droplet volume was in the order of several hundred picoliters. Preliminary inkjet printing on a paper was also demonstrated. This phenomenon is expected to be utilized for a new inkjet print head.