The instability of evaporating charged drops

Abstract

These studies constitute an extension of the work of Doyle, Moffett & Vonnegut (1964).Experiments showed that the evaporation of a charged droplet of water, aniline or toluene supported in a vertical electric field is accompanied by no discernible loss of charge and a consequent increase in electrical pressure in the drop surface owing to the decrease in radius. When the relationship between drop charge Q and radius R becomes consistent with the Rayleigh criterion the drop disintegrates at its uppermost point, where the electrical pressure is a maximum, to eject about 25% of its mass in the form of highly charged droplets. The measured relationship between the quantity of ejected charge, ΔQ, the mass loss, ΔM, and R was close to that derived theoretically from Rayleigh's equation, indicating that the value of ΔQ for a particular ΔM and R is approximately the theoretical minimum and that an individual drop may undergo a sequence of disintegrations, as was observed. The range of droplet radii studied by means of this technique was 30–200 μ.The absence of disintegrations during the evaporation of much larger charged drops suspended from insulating fibres was attributed to corona discharge.