The Mechanism of Coalescence of Liquid Drops

Abstract

The coalescence of two liquid drops, pressed against each other while a voltage is applied across the drops, has been studied with high-speed photography. The delay between contact and coalescence is of the order of milliseconds for distilled water, alcohols, and aqueous solutions of hydrochloric acid. The inverted value of this time, the rate of coalescence, is proportional to the voltage between the drops at low voltages and to the square of the voltage at high voltages. In both cases, the plot of rate against voltage extrapolates to zero rate at zero voltage. In the linear case the rate is proportional to (??1)½, in the parabolic case to ?, where ? is the dielectric constant. The following interpretation of the data is offered: Coalescence is effected by the formation of bonds across the interface between the drops. This may occur in two ways, by breaking of bonds and formation of new bonds, or by gradual rearrangement of bonds. In the former case, the rate is proportional to the energy in the drops and thereby to ? and the square of the voltage. In the latter case, the rate is proportional to (??1)½ and the voltage.