Measurements of the Krafft Point of Surfactant Molecular Complexes: Insights into the Intricacies of “Solubilization”

Abstract

Of the surfactant molecular complexes widely obtained by us in the system of quaternary ammonium cationic surfactants such as CTAB (cetyltrimethylammonium bromide) and various aromatic substances as additives, we have already reported several solution characteristics which reveal them to be novel surfactant species. In the report it was disclosed that they had their own critical micelle concentrations (cmc's) different from those of the mother surfactants and that the solubilization of such surfactants−solubilizates (additives) was just the dissolution of the surfactant complexes generated in the solubilization processes. In this successive study through measurements of the Krafft point of the surfactant molecular complexes, it will again be clarified that the “solubilization” is not a special phenomenon but merely one which is recognized to be the dissolution of those surfactant complexes like that of any other crystalline material. The facts that the solubilization is obviously operative even at such a low surfactant concentration as below its cmc and that the presence of surfactants far above their cmc suppresses the solubilization to such an extent that it is much lower than that of the solubility of the solubilizates in pure water might be explained only by the novel concept we already presented, by which the obsolete theory for the solubilization so far should be substituted.