Ion-dipole induced interaction between cationic gemini/TTAB and nonionic (Tween) surfactants: interfacial and microstructural phenomena

Abstract

The present work is focused at studying the interactions between alkanediyl-α, ω-bis(tetradecyldimethylammonium) dibromide type cationic gemini surfactants, 14-s-14 (s = 4, 5, and 6) and conventional nonionic Tweens (Tween 20, Tween 40, Tween 60, and Tween 80) and to attain a comparison with their monomeric counterpart tetradecyltrimethylammonium bromide (TTAB). The critical micelle concentrations (cmc) of mixtures of varying compositions have been evaluated using surface tension measurements. The molecular interaction parameters (β) at the monolayer air–water interface and in bulk, standard free energy of micellization (ΔG°_mic), excess free energy of mixing (ΔG°_ex), Gibbs energy of adsorption (ΔG°_ad), and activity coefficients for the constituents in the mixtures (f_i) were evaluated by employing the Clint, Rubingh, and Rosen approaches. All the parameters indicate synergism in the systems and effective involvement of the nonionic (Tween) component in the mixtures. Micelle aggregation numbers (N_agg), obtained using steady-state fluorescence quenching technique, also indicate enrichment of mixed micelles with Tweens. The micropolarity, dielectric constant and Stern–Volmer binding constants (K_sv) of the mixed systems have also been evaluated from the fluorescence data. Three-dimensional fluorescence spectroscopy has also been performed for better understanding of the quenching experiments.