Asian Journal of Chemical Sciences

The effect of selected alcohols on the surface characteristics of the cationic gemini surfactant hexanediyl-1,6-bis (dimethyldodecylammonium bromide) (12-6-12) was investigated using surface tension measurements at 303.15 K. The evaluated surface parameters included the critical micelle concentration (CMC), C₂₀ (the concentration required to decrease the surface tension of water by 20 mN m^-1), maximum surface excess (Γ_max), minimum molecular area (A_min), the CMC/C₂₀ ratio and surface pressure at the CMC (Π_CMC). These parameters were used to assess the influence of selected alcohols on mixed micelle formation and adsorption behaviour. The results showed that alcohol addition appreciably affected the interfacial and micellization properties of the gemini surfactant. In all systems studied, increasing the alcohol concentration caused a progressive decrease in the CMC, indicating facilitated micelle formation. The extent of this effect depended on the molecular structure and chain length of the alcohol, suggesting favourable hydrophobic interactions between the alcohol molecules and the surfactant aggregates. The calculated thermodynamic parameters, including the standard Gibbs free energy of adsorption (ΔG°_ads) and the minimum free energy at the air-water interface (G^(s)_min)), indicated that alcohol addition promoted spontaneous adsorption and improved interfacial stability. The increase in surface excess, together with the reduction in molecular area, further indicated closer packing of surfactant molecules at the interface.