Experimental analysis of the evolution of an electrified drop following high voltage switching

We report experimental results on the electrohydrodynamic behavior of drops following high voltage switching. A pendant drop was placed between two parallel electrodes. Then, a DC high voltage power supply was switched on. The voltage difference between the two electrodes reached the prescribed value through an exponential relaxation process with a characteristic time of the order of some tenths of a second. The drop's free surface deformation was precisely measured as a function of time. The drop's evolution can be regarded as a quasi-equilibrium process for subcritical voltages. The instantaneous free surface deformation perfectly matched the equilibrium solution for a voltage which increased over time. The rate at which the electric charge migrated to the free surface was measured precisely by fitting the equilibrium solution to the experimental free surface deformation. For supercritical voltages, the drop's evolution consisted of two stages: a quasi-equilibrium process until the voltage difference reached its critical value, and a dynamical regime driven by the surface tension force and leading to the drop's breakage. (c) 2012 Elsevier Masson SAS. All rights reserved.