Electrification accompanying the bursting of bubbles in water and dilute aqueous solutions

Abstract

The electric charges carried on the drops ejected from air bubbles bursting at the surface of water and aqueous solutions have been measured in relation to the bubble size and the concentration of the solution. Drops ejected from pure water and solutions of concentration less than about 10^–4 M carry a negative charge, the magnitude of which decreases rapidly with increasing concentration and becomes vanishingly small at concentrations greater than about 10^–4 M. For more concentrated solutions the drops carry a small positive charge. The negative charging of the drops is explained quantitatively by a thin film of water rising from the inner surface of the bubble cavity to form a small jet that breaks up to produce the drops, their charge resulting from the rupture of the electrical double layer at the air/water interface. The depth of the diffuse double layer is less in solutions of higher concentration and this accounts for the smaller charges on the drops. The positive charging of the drops at high concentrations is attributed to the separation of charge during the break-up of an initially uncharged varicose jet, when water containing an excess of positive ions is forced into the swelling regions that form the drops from the constricting necks between them.