The Surface Activity of Tetrabutylammonium Halides in the Aqueous Solutions

Abstract

Abstract The surface activity of the tetrabutylammonium halides at the air/aqueous solution interface or at the hexane/aqueous solution interface has been studied. The surface or inter facial tension versus the concentration curves of the electrolytes are markedly dependent on the kind of their counter-ions, just as with these electrolytes in aqueous solutions. The surface activity of tetrabutylammonium iodide is fairly strong; it approximately corresponds to that of the surface-active straight-chain electrolyte with an octyl group. From the thermodynamic parameters of the adsorption of tetrabutylammonium iodide, it is found that the standard free energy of adsorption becomes negative as a result of the large positive values of the standard entropy of adsorption, irrespective of the positive values of the standard enthalpy change. This suggests that the adsorption is a “hydrophobic” effect; that is, the “icebergs” around the nonpolar groups of the electrolyte return to the original water by the process of the transfer of the hydrophobic ions from the aqueous solution to the surface phase.