Specific ion adsorption on alkyl carboxylate surfactant layers

Mixtures of dodecyl carboxylate, CsOH, RbOH and octanol in D2O were investigated to determine the relative ion specificity of Cs+ and Rb+ in their interactions with dodecyl carboxylate in a liquid crystalline phase. Octanol as cosurfactant was necessary to obtain the lamellar liquid crystalline phase. The technique used was the measurement of the NMR quadrupole splitting of 137Cs and 87Rb. The ratio of Rb to Cs was varied as well as the concentration of surfactant and octanol, whereas the ratio of surfactant to octanol was kept constant at 1:3. It turned out that there is no significant difference between both ions in their affinity towards carboxylate head groups.