Formation of highly charged nanodroplets by condensation–electrospray device

Abstract A novel electrospray device is developed to generate highly charged nanodroplets from dew-condensed water. The device is composed of a discharge electrode with a spherical tip, ground electrode, Peltier cooling device, and high voltage power supply. When the surface temperature of the discharge electrode reaches the dew point of surrounding room air, a liquid water film is formed on the discharge electrode. Pulsating cone-jet mode electrospray is generated by applying negative 5 kV high voltage to the discharge electrode. Highly charged macrodroplets are ejected from the tip of water cone and they are externally charged by the collision of unipolar negative ions. As the droplets shrink by the evaporation while keeping the number of charges, the droplets undergo Coulombic fission and/or electron emission when the number of charges exceeds the charge retention limits. The resulting change in the electrical mobility distribution and the number of charge are measured by the aerosol measurement techniques. It is found that droplets carry 3 to 23 elementary charges and the charge distribution has a peak at n =8.