Effect of polar organic solvents on the surface adsorption and micelle formation of surface active ionic liquid 1-dodecyl-3-methylimidazolium bromide in aqueous solutions and comparison with the traditional cationic surfactant dodecyltrimethylammonium bromide

Abstract

The effects of polar organic solvents methanol, ethanol, n-propanol, n-butanol, ethylene glycol and propylene glycol on the micellization and surface adsorption behavior of surface active ionic liquid (SAIL) 1-dodecyl-3-methylimidazolium bromide (DDMIm-Br) and traditional cationic surfactant dodecyltrimethylammonium bromide (DTAB) have been studied by experimentally measured electrical conductivities and surface tensions. The main focus was on the effect of added organic solvents on the critical micelle concentration (cmc), degree of counterion dissociation on the micelles (α), surface tension at the cmc (γcmc), adsorption efficiency (pC20), effectiveness of surface tension reduction (Πcmc), the maximum surface excess concentration (Γmax), minimum surface area per molecule (Amin) at interface of air/solution and standard Gibbs free energy of micellization (ΔGm∘) of both the investigated surfactants in aqueous solutions. The results show that methanol, ethanol, ethylene glycol and propylene glycol act as a cosolvent and slightly increase the cmc of both surfactants in aqueous solutions. However the more hydrophobic solvents n-propanol and n-butanol, act as a cosurfactant and decrease the cmc by their presence. The accepted correlations were found between the different interfacial properties and the relative permittivity of the added organic solvents. As the difference between the relative permittivity of added organic solvent and that of pure water becomes smaller than about 35, the adsorption and micellization behavior of the surfactants in different organic solvents–water mixed media shifts to those in pure water. Finally a comparison was made between the surface active imidazolium-based ionic liquids and traditional cationic surfactants in respect to the effects of organic solvents on their surface activity and aggregation behavior in aqueous solutions.