AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Coulombic Fission of Ionic Salt Solution Droplets at Super-Rayleigh Limits
ASIT RAY, Kuo-Yen Li, University of Kentucky
Abstract Number: 355 Working Group: Aerosol Physics
Abstract Evaporation of neutral solvent from a charged solution droplet causes reduction in the droplet size, and an increase in the surface charge density. Ultimately, the charge density attains a critical limit where the droplet becomes unstable, and it regains stability by emitting a fraction of its charge and mass in the form of progeny droplets. The process is referred to as the Coulombic fission which has been confirmed to occur at the Rayleigh limit by numerous experiments. In this study we have examined the effects of ionic salts on Coulombic fission of evaporating microdroplets. Experiments were conducted on single charged droplets that were suspended in an electrodynamic balance. A resonance based light scattering technique was used to determine the size and the size change of a droplet at a charge instability induced fission, while the charge level and the charge loss were obtained from the dc voltages required to gravitationally balance the droplet. We have studied diethylene glycol and triethylene glycol droplets containing lithium chloride or calcium chloride at varying concentrations. The results of the present study on droplets containing ionic salts show that droplet fissions occur at significantly higher charge levels than the Rayleigh limit. The charge limit at a fission depends on the salt concentration in a droplet and increases as the concentration increases. When a droplet undergoes multiple fissions we observed that the charge level of a succeeding fission is always higher than preceding one due the concentrating effect of the salt. The observed charge limit increases linearly with the increasing concentration below the saturation point, and above the saturation value, the dependence of the charge stability limit on the concentration changes considerably due to the precipitation of solute at the droplet surface. Lithium chloride had more pronounced effect on the observed charge limit than calcium chloride.