Micellization behaviour and thermodynamic parameters of 12-2-12 gemini surfactant in (water + organic solvent) mixtures

The effect of organic solvents on micellization behaviour and thermodynamic parameters of a cationic gemini (dimeric) surfactant, C12H25(CH3)2N+–(CH2)2–N+(CH3)2C12H25·2Br−, (12-2-12) was studied in aqueous solutions over the range of T = (293.15 to 323.15) K using the conductometric technique. Ethylene glycol (EG), dimethylsulfoxide (DMSO) and 1,4-dioxan (DO) were used as organic solvents with three different contents. The critical micelle concentration (cmc) and the degree of counter ion dissociation (α) of micelles in the water and in the (water + organic solvent) mixtures including 10%, 20%, and 30% solvent contents were determined. The standard Gibbs free energy (ΔGm∘), enthalpy (ΔHm∘) and entropy (ΔSm∘) of micellization were estimated from the temperature dependence of the cmc values. It was observed that the critical micelle concentration of the gemini surfactant and the degree of counter ion dissociation of the micelle increased as the volume percentage of organic solvent, and temperature increased. The standard Gibbs free energy of micellization was found to be less negative with the increase in the organic solvent content and temperature.

► The cmc and α   values of surfactant increased with increasing solvent content and temperature.
► The values of (ΔGm∘) are negative in all cases for the micelle formation becomes less favourable.
► The values of negative enthalpy indicate importance of the London dispersion forces for the micellization.
► The positive entropy is due to a contribution supplied from the solvent.