title: Short range attraction between two similarly charged silica surfaces.
abstract: Using an atomic force microscope we measure the interaction between two identically charged silica surfaces in the presence of a saline solution. For pure NaCl the interaction is always repulsive. Upon addition of cobalt hexamine ions, Co(NH(3))(6)(+3), the repulsion is gradually suppressed and a pronounced attraction develops at distances much shorter than the screening length. Higher concentrations of cobalt hexamine turn the attraction back into repulsion. Measurements of surface charge renormalization by the trivalent cations provide their surface density and their association constant to the negatively charged silica surface. These estimates tend to exclude interaction between two condensed Wigner crystals as an explanation for the attraction.
authors.affiliation: Faculty of Physics and the Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology, Haifa.
authors.forename: Ohad
authors.initials: O
authors.lastname: Zohar
authors.forename: Ilya
authors.initials: I
authors.lastname: Leizerson
authors.forename: Uri
authors.initials: U
authors.lastname: Sivan
mesh_terms: D000327:Adsorption; D003035:Cobalt / Q000737:chemistry / Q000494:pharmacology; D007477:Ions; D018625:Microscopy, Atomic Force; D012822:Silicon Dioxide / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D007477:Ions; C032300:hexaamminecobalt(II); D003035:Cobalt; D012965:Sodium Chloride; D012822:Silicon Dioxide