The Interaction between Zwitterionic Hydrocarbon and Anionic Fluorocarbon Surfactants in Dilute and Concentrated Aqueous Solutions

The interaction between a zwitterionic hydrocarbon surfactant, N-tetradecyl-N,N-dimethyl betaine (TNB) and an anionic fiuorocarbon surfactant, lithium perfluorooctanesulfonate (LiFOS) in dilute aqueous solution in the presence of 0.01 moldm^-3 LiCl has been investigated by means of surface tension, static and dynamic light scattering, solubilization of water-insoluble dye, fluorescence probing and rheological measurements. The same system in concentrated aqueous solution has been characterized from the phase diagram. In the concentrated system, the lamellar liquid crystal phase forms at low surfactant concentrations over a wide region. The L₃ phase has been observed at composition weight ratio of TNB:LiFOS = 0.7:0.3 (molar function of TNB, X_TNB = 0.8). On the other hand, the mixed system in dilute aqueous solutions has shown a composition dependence of micellar properties and synergistic effect. At X_TNB = 0.8, the solubilized amount of a water-insoluble dye and relative viscos ities have shown maxima, whereas the diffusion coefficient has shown a minimum. A strong shear dependence has been observed at X_TNB = 0.8. The L₃ phase aggregates consist of plate-like micelles.