Experimental observation of end-pinching in the Rayleigh breakup of an electrodynamically levitated charged droplet
The experimental time-lapse images of the breakup phenomenon of a charged droplet (diameter ~100-300 micro-m) levitated in an electrodynamic (ED) balance is reported. During the breakup process, a levitated charged droplet undergoes evaporation leading to a reduction in droplet size and increase in the corresponding surface charge density. As the surface charge density reaches to a critical value, known as the Rayleigh limit, the droplet undergoes breakup by forming a jet which further ejects highly charged progeny droplets. All the successive events of the droplet breakup process such as drop deformation, breakup, and relaxation of the drop back to spherical shape after ejection of progeny droplets have been recorded using the high-speed camera at 1.3 hundred thousand frames per second. The droplet is observed to eject 3-5 progeny droplets from a jet indicating end pinching mode of breakup. The jet is then observed to relax back after ejecting 31% of the total charge and ~3\% of the total mass. A suitable theory is provided to supplement the experimental observations, and a reasonable agreement is observed. Additionally, the theory is extended for the prediction of total mass loss and the entire lifetime of a charged droplet.