Ana Čop

Reversible charging of the ice–water interface: II. Estimation of equilibrium parameters

An ice electrode was constructed in order to measure dependency of the surface potential on pH. The electrode had a Plexiglas body with a platinum plate on the bottom, which was cooled by passing the cooling liquid through a tube mounted inside the electrode. The temperature inside the electrode was -7 degrees C, while the electrolyte solution was kept at 0.02 degrees C, so that an ice layer was formed on the platinum plate. In the acidic region fast equilibration of electrode was observed. The slope dphi(0)/dpH was found to be between -40 and -46 mV. The maximum of the slope was observed at pH 4.4, which coincides with the isoelectric point of ice-water interface. In the basic region the equilibration was slow and more pronounced deviation from the Nernstian behavior was observed. The results were explained on the basis of the surface complexation model, assuming an amphotheric nature of surface OH groups. In the basic region the surface bears high negative charge so that binding of sodium ions at the interface influenced the results. Copyright 2000 Academic Press.

Interfacial equilibria at a goethite aqueous interface in the presence of amino acids

Adsorption of o-, m- and p-aminobenzoic acid on goethite was investigated by means of adsorption and electrokinetic measurements and was interpreted on the basis of the surface complexation model (SCM). All three acids examined showed similar behavior, with adsorption maximum at pH 4.5, while the adsorption affinity decreased in the order p-, o-, m-aminobenzoic acid. Electrokinetic measurements indicated that isoelectric points of goethite with adsorbed amino acids were shifted to lower pH values with respect to goethite in absence of amino acids, suggesting adsorption of negatively charged species (-1). This conclusion was confirmed by calculations based on the SCM. The equilibrium constant for exchange of Cl- ions with amino acid ions (-1) were determined as logK A/L = 2.62 ± 0.13 for o-aminobenzoic acid, logK A/L = 2.37 ± 0.11 for m-aminobenzoic acid and logK A/L = 2.85 ± 0.14 for p-aminobenzoic acid.

Equilibrium of counterion association in micellar systems: cetyltrimethylammoniumbromide

Equilibrium of counterion association in micellar systems: cetyltrimethylammoniumbromide Surface Complexation Model was applied for the analysis of counterion association in the micellar systems. The equilibrium in cetyltrimethylammoniumbromide (CtaBr) solution was examined. Thermodynamic equilibrium constant was calculated using experimental data obtained with ion-selective electrodes (silver/silver bromide and surfactant electrode).