Isoelectric point (iep) of water at inert and hydrophobic surfaces was found to be close to pH 3 which means that interfacial water is negatively charged in a broad pH region above e.g. pH 4. Accordingly, the charge of interfacial water layer contributes to net charge of colloid particles dispersed in aqueous medium so that isoelectric points of silver halides measured at pH 7 do not represent electroneutral surface with respect to adsorption of silver and halide ions. However, values of iep measured at pH 3 may be used as electroneutrality point. The equlilibrium constants for adsorption of silver and halide ions, as obtained from surface potential data, were corrected accordingly. Interpretation of electrokinetic and surface potential data for water/air interface leads to conclusion that ionization of interfacial water layer is significantly more pronounced with respect to the bulk water.

Water at inert and hydrophobic surfaces

244th National Meeting (2012)

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