Mixed Micellization and Density Functional Theory (DFT) Studies on the Molecular Interactions between Gemini and Nonionic Surfactants

In the present study, the mixed micellization behavior of gemini surfactant-1, 5-bis (N-hexadecyl- N, N-dimethylammonium) pentane dibromide (G5) with non-ionic surfactant triton X-100 (TX-100) was investigated in the micellar phase by utilizing the conductometric technique. The deviation of ideal critical micelle concentration (cmc*) from experimental critical micelle concentration (cmc) has been estimated using well-known Clint's theory of mixed micelles. The regular solution approximation was used to determine the interaction parameter (β) and found to be negative. The negative values of β at all mole fractions confirm an attractive interaction between two mixed components. The activity coefficients and excess Gibbs free energy of mixed micelles have been calculated by using different approximations, like Rubingh, Lange and Motomura. Counterion binding (g) computed from the post and premicellar slopes of specific conductance vs. concentration graph. Overall, in most of cases, in presence of TX-100, the counterion binding of gemini surfactant was found to be less in magnitude. The molecular interaction was also investigated by the density function theory (DFT). A polarizable continuum model (PCM) was used (with water as a solvent) to optimize the single surfactants and their mixture. The computational process was carried out by the B3LYP method and the 6-31G basis set.