The surface charge of an open water surface is crucial
for solvation
phenomena and interfacial processes in aqueous systems. However, the
magnitude of the charge is controversial, and the physical mechanism
of charging remains incompletely understood. Here we identify a previously
overlooked physical mechanism determining the surface charge of water.
Using accurate charge measurements of water microdrops, we demonstrate
that the water surface charge originates from the electrostatic effects
in the contact line vicinity of three phases, one of which is water.
Our experiments, theory, and simulations provide evidence that a junction
of two aqueous interfaces (e.g., liquid–solid and liquid–air)
develops a pH-dependent contact potential difference Δϕ due to the longitudinal charge redistribution between two contacting
interfaces. This universal static charging mechanism may have implications
for the origin of electrical potentials in biological, nanofluidic,
and electrochemical systems and helps to predict and control the surface
charge of water in various experimental environments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.