Interaction of oxy-diester-linked cationic gemini surfactants with nonionic amphiphiles in aqueous medium

We have investigated the interaction of nonionic conventional surfactants, Brij 35 and Brij 58, with three homologous oxy-diester-linked cationic gemini surfactants, 2,2′-[(oxybis(ethane-1,2-diyl))bis(oxy)]bis(N-alkyl-N,N-dimethyl-2-oxoethanaminium) dichloride (C _m -DEG-C _m , m = 12, 14, 16), by the surface tension measurements at 30 °C. The tensiometric data were used to calculate the critical micelle concentration (cmc) of the pure and mixed (equimolar) gemini–conventional surfactant systems. cmc values of the gemini surfactants are well below those of their monomeric counterparts which contain the same number of carbon atoms in the hydrophobic tail per polar head group. From the experimentally obtained cmc values of the binary surfactant mixtures (1:1), various physicochemical parameters were calculated. Lower cmc values of the binary solutions than the ideal cmc and also the negative β ^m values indicate that the interactions between the component surfactants of the mixed systems are synergistic in nature; the C₁₆-DEG-C₁₆ + Brij 58 system is an exception, in which antagonism is observed. The occurrence of mixed micellization is indicated by the decrease in cmc of the binary surfactant solutions and nonideality of the mixed systems. Interaction parameters (β ^m , β ^σ ) of the mixed systems were evaluated by using the theoretical models suggested by Clint, Rubingh, and Rosen. Negative values of β and \( \varDelta {G}_{\mathrm{ex}}^m \) (excess free energy of mixing) indicate an overall attractive force in the mixed state. The cationic gemini surfactant with lower chain length shows higher interaction with the nonionic conventional surfactants.