Investigations of the Mechanisms of the Electrostatic Droplet Ejections

Abstract

This paper presents an experimental investigation of a micro dripping mode of electrostatic droplet ejection for the liquid solvents, such as DI water, acetone, dioxane, dioxane+ DI water (10% ,25% ,50% ,66.7%), of different physical properties. Emphasis is given to how the electrical conductivities of liquid solvents affect the stability of a micro dripping mode of drop-on-demand droplet ejection. The experimentation is based on a pair of electroplate with a hole at the center and a micro capillary tube with a pole inside, and on capturing the images of droplet ejection by a high speed camera. The results clearly demonstrate the influence of the applied voltage, the liquid conductivity and the in-flow rate on the formation of stable droplets for a micro dripping mode of droplet ejection. Especially, it is discovered that, given the applied voltage and flow rate, there exists an optimal range of conductivity, from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> S/cm, required for stable droplet ejection in a micro dripping mode. This may be compared with the earlier report on the range of liquid conductivity, from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-17</sup> S/cm to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> S/cm or larger, necessary for successful electrostatic spraying of liquid paraffin. This could be accounted for in terms of the electric force high enough for pulling away a droplet from the meniscus, but low enough for keeping the droplet from atomizing, which is something to do with charge relaxation time