Dynamic surface tension of aqueous surfactant solutions. 6. Compounds containing two hydrophilic head groups and two or three hydrophobic groups and their mixtures with other surfactants

Dynamic surface tensions (γ_t)—measured by the maximum bubble pressure method—of some surfactants containing two hydrophilic (sulfonate) groups and two or three hydrophobic groups in the molecule (“gemini surfactants”), and of their mixtures with a nonionic surfactant or an amine oxide, have been measured at 25°C in 0.1 M NaCl. Linearity of the plots of surface pressure vs. square root of the surface age indicated that the systems studied were all diffusion-controlled. For the individual surfactant systems, the apparent diffusion coefficient decreases with an increase in the number of alkyl chains and the bulkiness of the surfactant molecules. For the mixtures, when interaction between the two surfactants is weak, γ_t at short times (t<1s) is close to that of the component with the lower surface tension; at longer times, it is closer to that of the component with the lower equilibrium surface tension. When interaction is strong, γ_t at short times is greater than that of either component. The molar ratio at which maximum effect on γ_t is observed depends upon the strength of the interactions between the two surfactants.