Analysis of Surface and Micellar Phases in Binary mixture of Surfactant and Ionic Liquid by Surface Tension Measurement

Recently, ionic liquids with surface-active properties due to the specific characteristics (such as green solvent) have been considered. In this research, the interfacial and micellization behaviors of binary mixtures of an ionic liquid (1-hexyl 3-methylimidazolium chloride or C6mimCl) and cationic surfactant (Cetyltrimethyl ammonium bromide or CTAB) were studied at various mole fractions (0.1-0.9). The surface tension technique was used to determine CMC values of surfactants in pure and mixed states.
In the pure components, the weak interactions between C6mimCl and water (compared with CTAB and water) increase the tendency of CTAB to adsorb at the liquid–vapor interface (higher hydrophobicity and lower CMC for CTAB). The Experimental results were analyzed according to the regular solution model developed by Client, Rubingh, Rosen and others. Interaction parameter (βm), mole fractions ( ), activity coefficients ( ) were calculated and analyzed at the micellar phase.
Also, the thermodynamic parameters such as maximum surface excess (max), surface pressure ()and minimum area per molecule (Amin) calculated and investigated. The results show that the activity coefficients values are less than unity for studied system, indicating non-ideal behavior and attractive interactions between ionic liquid molecules and surfactants in the mixed micelles. Negative interaction parameter (βm) of the systems at the mixed micelle indicates the synergism of the mixing process. By reducing the surface tension (σ) increased the values of max (or decreased the values of Amin).