Electrosorption from pseudobinary surfactant mixtures: II. Binary surfactant mixtures of weakly adsorbable components investigated by electrocapillarity

Abstract

The electrocapillary curves of the mixtures hexahydrophenol/i-butanol and n-butanol/triethylamine-hydrochloride, respectively, were measured by the drop time technique in aqueous electrolyte solutions (1 M KCl) at different mole fractions and concentrations of the surfactants. The electrocapillary data were evaluated by the method of Hutchinson, and the total surface excess concentrations, the surface excess concentrations of the components in the mixed adsorption layer, and their mole fractions have been determined. In the system hexahydrophenol/i-butanol the adsorbability is different but both components have the same potential of maximum adsorption. It could be shown that the hexahydrophenol is adsorbed preferably above the concentration c > 3 × 10 −3 M; i.e., the mole fraction of hexahydrophenol in the interface is larger than the mole fraction of i-butanol. In the system n-butanol/triethylaminehydrochloride the adsorbabilities at the potentials of maximum adsorption are similar, but the potentials of maximum adsorption are very different ( E = −0.6 V; E = −1.0 V). It could be shown that at very negative potentials, a potential-dependent “demixing” of the surface phase occurs; i.e., at very negative potentials only triethylaminehydrochloride is adsorbed while the n-butanol molecules are displaced from the electrode surface.