Salt Effect on Mixed Micelle and Interfacial Properties of Conventional Cationic Surfactants and the Ionic Liquid Surfactant 1-Tetradecyl-3-methylimidazolium Bromide ([C14mim]Br)

The surface properties and mixed micellization behavior of binary combinations of an ionic liquid surfactant, namely, 1-tetradecyl-3-methylimidazolium bromide (C₁₄mim]Br) with common cationic surfactants viz. tetradecyltrimethylammonium bromide and tetradecylpyridinium bromide in the presence of sodium bromide (NaBr) were investigated by surface tension and conductivity measurements. The critical micelle concentration (CMC) and interfacial parameters, such as the maximum surface excess (Γ_max), minimum area per molecule (A_min) and surface pressure at the CMC (π_CMC) were determined from the surface tension data. The CMC and Γ_max values were found to decrease with increasing salt concentrations. The $ \Updelta G_{\text{ad}}^{ \circ } $ and $ \Updelta G_{\text{m}}^{ \circ } $ values are negative indicating the spontaneity of micelle formation.