title: Direct Observation of Confinement-Induced Charge Inversion at a Metal Surface.
abstract: Surface interactions across water are central to areas from nanomedicine to colloidal stability. They are predominantly a combination of attractive but short-ranged dispersive (van der Waals) forces, and long-ranged electrostatic forces between the charged surfaces. Here we show, using a surface force balance, that electrostatic forces between two surfaces across water, one at constant charge while the other (a molecularly smooth metal surface) is at constant potential of the same sign, may revert smoothly from repulsion to attraction on progressive confinement of the aqueous intersurface gap. This remarkable effect, long predicted theoretically in the classic Gouy-Chapman (Poisson-Boltzmann) model but never previously experimentally observed, unambiguously demonstrates surface charge reversal at the metal-water surface. This experimental confirmation emphasizes the implications for interactions of dielectrics with metal surfaces in aqueous media.
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Ran
authors.initials: R
authors.lastname: Tivony
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Dan Ben
authors.initials: DB
authors.lastname: Yaakov
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Gilad
authors.initials: G
authors.lastname: Silbert
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Jacob
authors.initials: J
authors.lastname: Klein
mesh_terms: D008670:Metals / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D008670:Metals