Toroidal-droplet instabilities in the presence of charge.

Abstract

Neutral toroidal droplets can break via the surface-tension-driven Rayleigh-Plateau instability. They can additionally exhibit a shrinking instability, which is also driven by surface tension, whereby the handle progressively disappears. We find that charging a toroidal droplet can qualitatively change the behavior and cause the droplet to expand. We successfully model the transition from shrinking to expanding, considering the pressure balance across the interface of the torus. However, despite the change in behavior, charged toroidal droplets end up breaking into spherical droplets. We quantify how the wavelength of the fastest unstable mode associated to this breakup depends on the applied voltage and compare the results with theoretical expectations for charged cylindrical jets.