engleski

Charging of water at inert surface

Electrokinetic measurements of bubbles (argon or nitrogen) in aqueous electrolyte solution obeyed negative surface charge (charge of stagnant interfacial water layer) in the region of pH > 3, and positive in the region pH < 3 [1]. This finding was interpreted as preferential accumulation of OH– ions at the surface, with respect to H3O+ ions accumulation. Similar findings were obtained for the interfacial properties of other inert (hydrophobic) materials (such as hydrocarbon oils, Teflon, ice, diamond, etc.) [2]. The fast and simple method for measurement of electrokinetic properties of argon bubbles in aqueous electrolyte solution was introduced. It was found that bubbles in a contact with the ceramic frit of reference electrode affected the measured electrode potential i.e. contact potential. The contact potential depends on pH (it is zero near pH ≈3) and ionic strength (decreasing with increase of electrolyte concentration) [3]. Surface tension data for air/water interface was interpreted by comprehensive thermodynamic treatment without assumption of constant surface content. The theoretical analysis predicted a minimum of surface tension data and explained the experimental finding [4]. Additionally the surface properties of hydrophobic silver halides were analyzed from the results of surface potential and electrokinetic measurements [5]. It was found that pH doesn't influence the surface potential but shifts the isoelectric points of silver halides. This finding supports the hypothesis of different affinities of H3O+ and OH– ions within the interfacial water layer near hydrophobic surfaces.

inert surfaces ; electrokinetics ; air water interface ; electrical interfatial layer ; surface charge ; surface potential

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