High-speed imaging of Rayleigh breakup of charged droplets levitated in an electrodynamic balance

Electrospray is a well-known method for production of aerosols of nanometre size for various applications. An important question pertains to the Rayleigh break-up mechanisms which are responsible for the transformation of the micrometre sized droplets ejected from the Taylor cone into nano-sized particles. However, being a fast process, it is nearly impossible to carry out controlled observations of the break-up process in electrospray itself and hence the droplet is levitated in an ED balance. The quantitative observations such as jet diameter, charge and mass loss have been made on the droplets of about 70 to 200 μm size, having fissility 0.15-0.3. As the droplet undergoes evaporation, the droplet size decreases increasing the fissility, and it is observed that finally, the droplet breaks up in a succession of multiple ejections. All the successive events of droplet oscillations, deformation, breakup and relaxation of the drop after ejection have been captured by a high-speed camera connected with stereo-zoom at 130-220k fps. The experiments yield loss of about 29-40 % of original charge and 2 to 3 % of the original mass of the drop, with a jet diameter of 1 to 6 μm. The paper will discuss the quantification of these data along with the results of BEM simulations.