Conductometric and tensiometric studies on the mixed micellar systems of surface-active ionic liquid and cationic surfactants in aqueous medium

Abstract

Physicochemical properties of aqueous surfactant solutions can be suitably modified by the addition of room temperature surface-active ionic liquids (SAILs). As green solvents, these SAILs are used as the ideal additives for modifying the aqueous surfactant properties. Such mixed surfactant + SAIL systems in aqueous solutions find enormous applications in several technological fields. The changes in the micellar behavior of cationic surfactants cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) have been investigated in the presence of SAIL 1-decyl-3-methylimidazolium chloride [C10mim][Cl] employing conductometric and tensiometric methods. Micellar and interfacial parameters such as critical micelle concentration, cmc micellar mole fraction, X1, of component 1 (CPC/CPB), micellar interaction parameter, β, activity coefficients ƒ1 and ƒ2 of component 1 and component 2 (SAIL) in the mixed micelles, excess Gibbs free energy of micellization, ΔGex0, standard Gibbs free energy, ΔGmic0, enthalpy, ΔHmic0, and entropy, ΔSmic0 of micellization, surface excess concentration, Гmax, minimum surface area per molecule, Amin, and standard Gibbs free energy of adsorption ΔGad0 at the interface were evaluated. In addition, packing parameters of amphiphiles in the micelles, P, volume contribution of the hydrophobic chain, v, and its effective length, lC have also been evaluated for the pure and mixed systems. The interactions between CPC/CPB and SAIL in the mixtures are found to be non-ideal and synergistic, and that mixed micelles are richer in CPC/CPB monomers. Of the several interactive interactions, hydrophobic interaction seems to be dominant between the components of the mixed systems. Adsorption of SAIL molecules at air-solution interface is found to be richer in SAIL than CPC/CPB molecules, which is also supported by the higher negative ΔGad0 values than ΔGmic0values. The micelles/ mixed micelles formed have spherical geometry.