engleski

Physico-Chemical Properties of Asymmetric Catanionic Surfactants

A series of novel catanionic surfactants was prepared by mixing equimolar solutions of cationic (hexadecyltrimethylammonium bromide) and anionic (sodium alkyl sulfate, with the chain length C10, C12 and C14) surfactants. New compounds were characterized by optical microscopy, X-ray diffraction, IR spectroscopy, 1H NMR, and chemical analyses. The asymmetric catanionic surfactants exhibited a complex thermal behavior. Several successive phase transitions in the solid state were detected as shown by calorimetric, thermogravimetric and X-ray diffraction data and polarizing microscopy observation. On heating, several solid crystalline-solid crystalline, solid crystalline-liquid crystalline, and liquid crystalline-isotropic liquid phase transitions were observed. On cooling, however, all hexadecyl-trimethylammonium alkyl sulfates underwent reversible changes, exhibited a temperature hysteresis and an advanced ordering in the crystal lattice.

catanionic surfactants ; liquid crystals ; phase transitions ; polymorphism ; thermal analyis

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