Micellization behavior of gemini surfactants with hydroxyl substituted spacers in water and water-organic solvent mixed media: The spacer effect

Abstract

The micellization behavior of cationic gemini surfactants 1,3-bis(dodecyl-N,N-dimethylammonium bromide)-2-propanol [12-3(OH)-12,2Br−] and 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol [12-4(OH)2-12,2Br−] have been investigated in binary mixed media of water and organic solvents [1,4-dioxane (DO) and ethylene glycol (EG)] by conductivity measurements. The micellization behavior in aqueous medium has been studied using conductivity, steady-state fluorescence, zeta potential and dynamic light scattering measurements. The process of micellization is delayed with increasing amount of an organic co-solvent, as a result, there is a progressive increase in critical micelle concentration (cmc), Gibbs free energy of micellization (ΔGom) and Gibbs free energy of transfer (ΔGotrans). A good correlation between ΔGom and Gordon parameters suggests that the cohesiveness of the mixture is reduced in presence of an organic co-solvent. Better proneness of micellization in EG as compared to that in DO as co-solvent is because of resemblance of EG with water. Also, the chemical structures of spacer group of gemini surfactants have shown a significant effect on the aggregation and the thermodynamic properties of micellization. The micellization of 12-4(OH)2-12,2Br− is comparatively delayed than that of 12-3(OH)-12,2Br− in a given solvent system. The possible factors those can be responsible for the difference in cmc and that in ΔGom between two studied geminis have been discussed. There is compensation between enthalpy and entropy for the formation of micellar aggregates.