Fluorocarbon−Hydrocarbon Nonionic Surfactants Mixtures:  A Study of Their Miscibility

Binary mixtures of fluorocarbon and hydrocarbon nonionic surfactants derived from the tris(hydroxymethyl)acrylamidomethane (THAM) have been examined by ¹⁹F NMR spectroscopy and UV−visible spectroscopy in the presence of pinacyanol chloride as a probe. Aqueous solutions have been studied as a function of total surfactant concentration over a range of fluorocarbon/hydrocarbon ratios. For molar fractions in fluorinated surfactant lower than 0.7, the variations of both the ¹⁹F chemical shift and of the absorbance show two inflection points as a function of surfactant concentration. This was assigned to two critical micelle concentrations (cmc's). Above the second cmc, two kinds of micelles (fluorocarbon-rich and hydrocarbon-rich) should coexist as a result of the incompatibility between the two types of surfactants. The experimental results cannot be adequately described by current models on demixing micellar systems. An explanation of this behavior is suggested, by taking into account the interactions between the polyhydroxylated headgroups of the surfactants.