The double layer potentials at the toluene–aqueous interface in the presence of CTAB/NaBr. Implications for Ion-Selective Electrodes

The interfacial tension isotherms for cetyltrimethylammnonium bromide (CTAB) in the presence of sodium bromide at the aqueous–toluene interface are discussed. In accordance with previous observations for an aqueous–air interface, the presence of a non-surface active electrolyte (NaBr) has strong influence on the interfacial activity of CTAB at the aqueous–toluene interface. The results were analysed within the framework of the Surface quasi-Two Dimensional Electrolyte model (STDE), assuming that the non-surface active bromide counterions partially penetrate the Stern layer formed by cetyltrimethylammonium cations adsorbed at the interface. This analysis allowed for calculation of the electrical double layer (EDL) potentials (Stern potential and the diffuse double layer potential). The calculated EDL potentials were compared with the membrane potentials generated in the Ion-Selective Electrodes (ISE) containing neither ionophore nor ion-exchanger, when exposed to aqueous solutions of CTAB.