SOLID-PHASE TRANSITIONS OF CATIONIC SURFACTANTS

A series of catanionic surfactants were prepared by making an equimola r mixture of cationic (alkylammonium chloride) and anionic(sodium alky l sulfate) surfactants, both containing an isomer of the same chain le ngth, namely, C-10, C-12, or C-14 The prepared compounds exhibited com plex thermal behavior, characterized by several successive phase trans itions in the solid state as proved by differential scanning calorimet ry, X-ray diffraction, and optical birefringence observation using a p olarizing microscope. On heating, three main phase transitions were ob served for all compounds; solid crystalline-solid crystalline, solid c rystalline-liquid crystalline, and liquid crystalline-isotropic liquid . On cooling, all three compounds underwent reversibly the isotropic l iquid-liquid crystalline phase transition, while the liquid crystallin e-solid crystalline phase transition displayed peculiar properties. Ph ase transition temperatures increased with an increase in hydrocarbon chain length. (C) 1997 Academic Press.