Interaction between negative corona discharge and droplet emission from liquid Taylor cone

Abstract

We investigated the behavior of droplets, the Taylor cone tip, and discharge current characteristics in electrospraying with negative corona discharge, and analyzed the interaction among them in the time scale of several micro seconds. Negative corona discharges using 1 wt% sodium dodecyl sulfate solution or ethylene glycol as liquid cathode were investigated, and the discharge current pulse had a distinctive structure with serial pulse trains. The pulse train structure indicated that the discharges from the Taylor cone are in the form of Trichel pulses with a dynamic cathode. We found that the electric field, liquid conductivity, and liquid viscosity had no significant effect on the discharge current characteristics, with the exception of the current peak value, whereas a higher electric field or higher liquid viscosity led to extended pulse train intervals and durations. These effects can be attributed to the change in time scale of the cone tip curvature variation. The above results indicate that the curvature radius of the cone tip dominates the discharges from the Taylor cone. The emission and transfer of droplets between electrodes were observed using back-lit images and Mie-scattered light images taken by a high-speed camera. The droplet emission was synchronized with the leading current in the Trichel pulses. The terminal velocity of the droplets transferring discharge gap was proportional to the revised electric field. The experimental results indicate that the droplet emission mechanism from the Taylor cone with discharges is supposed to differ from that without discharges explained by the Rayleigh limit. The reasonable explanation for the droplet emission mechanism is that the droplets are torn off the liquid cone tip by the strong electric field associated with discharges.