Micellization and interaction properties of aqueous solutions of mixed cationic and nonionic surfactants

The micellization process of binary surfactant mixtures containing cationic surfactants viz. dodecyl pyridinium halide (C₁₂PyX; X=Cl, Br, I), tetradecyl pyridium bromide (C₁₄PyBr), and hexadecyl pyridium halide (C₁₆PyX; X=Cl, Br) and a nonionic surfactants viz. dodecyl nonapolyethylene glycol ether (C₁₂ E₉), dodecyl decapolyethylene glycol ether (C₁₂ E₁₀), dodecyl dodecapolyethylene glycol ether (C₁₂ E₁₂), and dodecyl pentadecapolyethylene glycol ether (C₁₂E₁₅) in water at different mole fractions (0-1) were studied by surface tension method. The composition of mixed micelles and the interaction parameter, β evaluated from the CMC data obtained by surface tension for different systems using Rubingh's theory were discussed. Activity coefficient (f1 and f2) of cationic surfactant (C_nPyBr)/C₁₂E_m (n=12, 14, 16 and m=10, 12, 15) mixed surfactant systems were evaluated, which shows extent of ideality of individual surfactant in mixed system. The stability factors for mixed micelles were also discussed by Maeda's approach, which was justified on the basis of steric factor due to difference in head group of nonionic surfactant.