Micellization and interfacial behavior of binary surfactant mixtures based on cationic geminis and nonionic Tweens

The behavior of mixed cationic gemini–nonionic surfactant systems in solution and at interface have been studied by surface tension measurements. Cationic geminis used were alkanediyl-α,ω-bis(dimethylhexadecylammonium bromide) and nonionic surfactants were the Tweens (Tween 20, 40, 60 and 80). The critical micelle concentration (cmc) values of the mixtures are lower than the values of individual surfactants and decrease with the increase in stoichiometric mole fraction of Tweens in the solution. This shows nonideal, synergistic mixing of the two components. Other parameters calculated were cmc at ideal mixing conditions (cmcid), surface excess concentration (Γexc) and minimum area per surfactant head group (Amin). The Gibbs energy of micellization ( Δ G m o ), Gibbs energy of adsorption ( Δ G ad o ), mole fraction of surfactants in mixed micelles ( X 1 m ) and monolayers ( X 1 σ ) , and interaction parameters (βm, βσ) were also evaluated. These values also indicate synergism in the system and greater contribution of the nonionic component in the mixtures.