Electric-Discharge-Mediated Jetting, Crowning, Bursting, and Atomization of a Droplet

We observe bursting, crown or jet formation, and atomization phenomena when electric discharge is confined at the base of a liquid droplet. Emulating an electrowetting-on-dielectric setup, a hemispherical droplet is placed on a cathode-isolator platform while a pointed anode from the top stimulates the discharge inside the drop. Beyond a critical intensity of the applied electric field, the dielectric layer under the droplet suffers breakdown to generate the discharge. Within a few milliseconds, the electric discharge stimulates crown or jet formation or bursting of the droplet. A lower (higher) salt loading in the droplet at lower (higher) field intensity leads to the jetting (bursting). The crown formation happens only for an intermediate window of salt loadings and electric field intensities. The energy conversion efficiency is found to be approximately $25\mathrm{%}$--$30\mathrm{%}$ for droplet bursting while the same is less than 2% for jet or crown formation. The experiments and simulations uncover that the location of the pointed electrode in the droplet and the separation distance of electrodes can be some crucial factors in varying the location of discharge, which eventually leads to the aforementioned flow morphologies. Further, the interplay between surface tension, viscous, and electric field forces inside the droplet is found to play crucial roles to engender the flow patterns. The setup transiently shows up the formation of end pinching of jets, microjets, high-aspect-ratio liquid threads, upward moving jet, liquid spikes riding on a crown rim, and capillary breakup of jets. Such electric-discharge-mediated droplet disintegration resembles closely the previously reported laser or plasma-induced phenomena. Further, with proper tuning of the aforementioned control parameters, the proposed methodology is expected to find its application in several cutting-edge technologies, such as inkjet printing, tissue ablation, or electroporation etc.