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 Cs-137 and Rb-87. 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. (C) 2014 Elsevier B.V. All rights reserved.