Forces and charges on an undeformable droplet in the DC field of a plate condenser

Abstract

A single conducting drop resting on the lower plane electrode of a horizontal condenser and surrounded by a dielectric fluid is considered. When a DC field is applied to the electrodes, the drop acquires electric charges and is subjected to an electrostatic force normal to the electrode. This driving force may eventually detach the drop if the applied field strength exceeds a threshold value. For small drops, the gravitational field and the electrical force effect can be neglected with respect to the surface tension. In this case, it may be assumed that drops are undeformable and keep a spherical cap shape. Based on this model, charges and forces are calculated analytically in any wetting conditions. To this end, previous studies concerning solid spheres are conveniently extended. The usefulness of the above model is then considered to determine the lift-off threshold value. For non-wetting conditions, new experimental results are presented: they fit precisely the derived theoretical lift-off conditions. For wetting conditions, the preceding calculations are shown to be unable to provide any testable criterion. The undeformability assumption has to be relaxed.

Wetting and evaporation of a sessile drop under an external electrical field: A review

“…The experimental studies summarised in Table 1, focused on the change in the contact angle for dielectric liquids under an external electric field varying from 1 to 25 kV/cm. The overall mean of these results suggested an increase or decrease in the contact angle with increasing magnitude of the electric field [17,[45][46][47][48][49][50].…”

Electro-Manipulation of Droplets for Microfluidic Applications

“…Previous experimental work on the deformation of sessile conductive drops in this geometry has included work on soap bubbles [2], polymer drops [13], water drops in air [3,6,14], water drops immersed in dielectric oil [15], and various alcohols in air [4,5,18]. As well as different liquids, these experiments also considered different substrate treatments (untreated, hydrophilic and hydrophobic), and therefore the initial contact angles of the drop varied greatly (specifically from from 15 to 160 degrees) [19].…”

Electric field induced deformation of hemispherical sessile droplets of ionic liquid

“…Previous quantitative experimental and theoretical work on the distortions produced in conducting liquids in this geometry includes on soap bubbles [13] [14] [15], water droplets [16], and water droplets immersed in dielectric oil [17]. In the current work we consider small distortions, in which the voltage-induced height increase is less than 5% of the initial height, for droplets with contact angles close to 90°.…”