Adsorption dynamics of binary mixture of Gemini surfactant and opposite-charged conventional surfactant in aqueous solution

The maximum bubble pressure technique has been used to study the adsorption kinetics of binary mixtures of an anionic Gemini surfactant C9pPHCNa with a cationic conventional surfactant C10TABr in aqueous solutions. The dynamic surface tension data were analyzed using the revised Ward and Tordai equations as well as the micelle dissociation kinetic model suggested by Joos et al. The apparent diffusion coefficient Da below the cmc, the adsorption barrier epsilona and the micelle dissociation constant kmic were obtained. The Da s at short times and at long times were respectively 0.2-16 x 10(10) and 0.08-0.9 x 10(10) m2s(-1), the latter corresponded to the adsorption barrier epsilona of 10-20 kJ mol(-1). The minimum epsilona appeared at the mole fraction of C9pPHCNa (alpha1, on a surfactant-only basis) in the bulk solution being 0.33. The kmic s of the mixed micelles were about 16-2300 s(-1). The most stable mixed micelles were formed at alpha1=0.2 rather than at alpha1=0.33 owing to great discrepancy of hydrophobicity between the two components. These results indicated that the composition of mixed solution was an important factor affecting the adsorption kinetics and the micelle stability.