Electrically charged droplet: case study of a simple generator

We studied the behavior of a simple apparatus that allows to charge droplets by induction. We imposed the following constraints (1) any liquid should be charged (mainly whatever its surface tension) and (2) the system is to remain as simple as possible. The design of the device results of a compromise regarding both constraints. The device developed is based on a planar capacitor in which the droplet are generated. The influence of the nature of the liquid (i.e. presence of ions in solution, polarity, surface tension and conductivity) on the charge induced was measured and was found to be independent of the liquid properties (except for the silicone oil). We deduced that, in the considered configuration, fluids behave like a “perfect conductor” as soon as conductive relaxation time is smaller than the droplet ejection time. Under this condition, the charge has the time to move in the droplet to reach the electrostatic regime.