Status: this preprint was under review for the journal ACP but the revision was not accepted.
The mechanism of spray electrification: the waterfall effect
James K. Beattie
James K. Beattie
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
Abstract. The waterfall effect describes the separation of charge by splashing at the base of a waterfall. Smaller drops that have a net negative charge are created, while larger drops and/or the bulk maintain overall charge neutrality with a net positive charge. Since it was first described by Lenard (1892) the effect has been confirmed many times, but a molecular explanation has not been available. Application of our fluctuation-correlation model of hydrophobic hydration accounts for the negative charge observed at aqueous interfaces with low permittivity materials. The negative surface charge observed in the waterfall effect is created by the preferential adsorption of hydroxide ions generated from the autolysis of water. On splashing, shear forces generate small negative drops from the surface, leaving a positive charge on the remaining large fragment. The waterfall effect is a manifestation of the general phenomenon of the negative charge at the interface between water and hydrophobic surfaces that is created by the preferential adsorption of hydroxide ions.
Received: 30 Oct 2015 – Discussion started: 13 Apr 2016
It has been known since the 19th c that the air around the base of a waterfall is negatively charged. These "air-ions" are thought to have beneficial health effects. From the acid-base properties of the droplets it was inferred that the negative charge was due to adsorbed hydroxide ions but the origin of these was obscure. In other work we have shown that water behaves similarly at all interfaces with low dielectric materials, whether air, oil or inert solids like Teflon.
It has been known since the 19th c that the air around the base of a waterfall is negatively...
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