Phase behavior and dynamic properties in mixed systems of anionic and cationic surfactants: lithium perfluorooctanesulfonate/diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) and lithium dodecyl sulfate/DEFUMAC aqueous mixtures

Two ternary phase diagrams of the cationic perfluorosurfactant diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) with an anionic perfluorosurfactant lithium perfluorooctanesulfonate (LiFOS) and an anionic hydrocarbon surfactant lithium dodecyl sulfate (LiDS) have been established at 25°C. The total surfactant concentration was less than 20wt%. In a wide mixing region of the LiFOS/DEFUMAC system, a lamellar-type phase,Pβ, was identified by its texture under a polarization microscope and by its x-ray diffraction pattern. Dispersed fragments ofPβ-phase are present in the dilute solutions in which one surfactant was in excess. The anisotropy of electrical conductivity, flow birefringence, dynamic light scattering, and electric briefringence demonstrate that thePβ fragments are disk-like with a radius of 0.7 μm. The disk-likePβ particles are transformed by shear into a spherical aggregate ofLα above a critical shear gradient. LiDS/DEFUMAC mixed solution forms dispersed and precipitatedLα in the dominant region. Radius and micropolarity of the dispersedLα aggregates are decreased as the ratio of LiDS:DEFUMAC approaches 1:1. On the basis of x-ray diffraction measurement the structure of precipitatedLα-phase seems to consist of monolayers.