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

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 11,4-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 (Delta G degrees(m)) and Gibbs free energy of transfer (Delta G degrees(trans)) A good correlation between Delta G degrees(m) 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 Delta G degrees(m), between two studied geminis have been discussed. There is compensation between enthalpy and entropy for the formation of micellar aggregates. (C) 2011 Elsevier B.V. All rights reserved.