Study on Mixed Micelles of Cationic Gemini Surfactants Having Hydroxyl Groups in the Spacers with Conventional Cationic Surfactants: Effects of Spacer Group and Hydrocarbon Tail Length

Gemini surfactants, being more surface-active than their conventional counterparts, have potential applications in various industries. The properties of mixed surfactant systems are far better than those of neat surfactants in many cases, and as a result, mixed surfactants are used in many industrial applications. In the present work, the micellar properties of binary mixtures of the monomeric cationic surfactants hexadecyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB) with the cationic gemini surfactants 1,3-bis(dodecyl-N,N-dimethylammonium bromide)-2-propanol and 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol were studied in aqueous solution at 303.15 K by means of conductivity, steady-state fluorescence, and fluorescence anisotropy techniques. The presence of a small amount of gemini surfactant was found to improve the physicochemical properties of the conventional surfactant For example, the cmc value of DTAB was reduced to one sixth of its original value in the presence of 0.1 mole fraction of a gemini surfactant. The spacer group of the gemini surfactant and the hydrocarbon chain of the monomeric surfactant play a significant role in the interactions between the surfactants in mixed micelles. These interactions are greatest when there are similarities in the structures of their hydrocarbon chains; however, the micellization process is favored by increasing hydrophobicity of the monomeric surfactant. The microenvironments of mixed micelles were studied using fluorescence techniques.