How specific are ion specificities? A pilot NMR study

Abstract

NMR quadruple splitting measurements are a useful technique to investigate the adsorption behaviour of ions near to charged surfaces in liquid crystals made of surfactants of different headgroups. In the present paper we show the differences in lithium and sodium adsorption on dodecyl carboxylate and dodecyl sulphate bilayers as a function of surfactant concentration and for two temperatures. To this purpose we mixed the pure surfactants and also mixtures of the lithium and sodium surfactants with octanol as a cosurfactant in appropriate ratios and concentrations to obtain liquid crystals. It turned out that the measured specific ion effects are much more pronounced in the case of carboxylates than for sulphates.