Noncontact rebound and fission of oppositely charged droplets

Abstract

Oppositely charged droplets rebound and break up under high enough electrical fields before they contact each other. By using high-speed microscopy, we present a detailed experimental study of the noncontact bouncing and breakup process of oppositely charged droplets for liquids of different conductivities. Under different applied voltages, the breakup morphology of oppositely charged droplets with various ion concentrations has been accurately captured, and an image-processing technology was used to analyze the effect of several parameters on the breakup process. The breakup structures based on ion concentrations were measured to build up their relationship to study the dynamic behavior of oppositely charged droplets. For poorly conducting or nonconducting liquids, no breakup behavior was observed regardless of the applied voltage. However, various breakup structures are detected as the applied voltage increases for high-conductivity liquids. The behavior of bouncing without breakup is caused by air discharge, which is achieved prior to the ion concentration on the droplet tip reaching the Rayleigh charge limit. The behavior of bouncing with breakup is a form of Coulomb fission, which means that the surface charge on the droplet tip reaches the Rayleigh charge limit prior to air discharge. The fitting curves are given to demarcate bouncing and breakup behaviors. Droplets with high conductivity exhibit the maximum change in breakup volume, indicating that high-conductivity liquids are more sensitive to changes in electric field strength.