Acidic microemulsions of dodecane/p-dodecyl-benzenesulfonic acid/water/mineral acid part 1. HLB acidity and phase behavior

Abstract The influence of strong mineral acids, such as hydrochloric and sulfuric acids, on the solubility regions in the system dodecane/ p -dodecylbenzenesulfonic acid/water was investigated. The solubility of the surfactant in water as well as the extent of the aqueous micellar solution are extremely sensitive to mineral acid concentration. An increase in the acid concentration causes a gradual change in the surfactant hydrophilic-lipophilic balance (HLB) value, transferring surfactant solubility from the aqueous phase to the oil phase via an intermediate surfactant phase, analogous to the behavior observed for nonionic surfactants with increasing temperature. Formation of the surfactant phase occurs at an optimum inorganic acid concentration or HLB acidity. The HLB acidity corresponds to the minimum amount of acidic surfactant which is able to dissolve concurrently large amounts of water and oil.