Fluorocarbon surfactant/water mesomorphic phases. Part 1.—A study of the ammonium perfluoro-octanoate + water system by optical microscopy and low angle X-ray diffraction

Abstract

The phase diagram of ammonium perfluoro-octanoate + water has been determined over the temperature range 298–373 K using a polarizing microscope. Low angle X-ray scattering measurements confirmed the existence of one isotropic and one lamellar liquid crystalline phase at 298 K. Evidence for the existence of a second isotropic phase was also obtained. The fluorocarbon + water phase diagram differs from the hydrocarbon + water system in that no hexagonal phase is formed, and the lamellar phase is formed at lower surfactant concentrations. The thickness of the fluorocarbon layer in the lamellar phase is less than that of the corresponding hydrocarbon at equivalent concentrations.