Effect of ethylene glycol on micellization and surface properties of Gemini surfactant solutions

Using surface tension and conductivity measurements, micellization of didodecyl dicationic dibromide Gemini surfactants of different methylene spacer lengths, 12-s-12, 2Br(-) (where s = 2, 4-methylene groups), is investigated in water-ethylene glycol (EG) mixtures with vol. percent of EG changing within the range of 0-30. Gibbs energy of mixed micellization (Delta G(mic)degrees) is obtained from the critical micelle concentration (CMC) and degree of counter-ion dissociation (alpha) values. Differences in the Gibbs energies of micellization of Gemini surfactants between water and water-EG mixtures are calculated in order to monitor the influence of EG on the micellization process. We determine transfer free energy (g(tr)) micelle formation for Gemini surfactants in mixed solvents using the Flory interaction parameter. CMC and micellar ionization degree increase with increase in the vol. percent of EG. The surface excess concentration (Gamma(max)) decreases and the minimum area per surfactant molecule (A(min)) increases with increase in the amount of EG present in the mixture. (C) 2010 Elsevier B.V. All rights reserved.