engleski

Solid Phase Transitions of Thermotropic Compounds

A novel catanionic symmetric and asymmetric surfactants are prepared from equimolar aqueous solutions of cationic and anionic surfactants. The composition, structure, morphology and thermal behavior of new compounds are determined by chemical, X-ray powder diffraction, IR, NMR spectra analyses, differential scanning calorimetry, thermogravimetry and polarizing microscopy. The thermal behavior of solid crystalline catanionic surfactants shows a complex polymorphism and thermotropic mesomorphism from the stable crystalline phase to the isotropic phase. The number of polymorphs, all of the bilayered structure, depends on the symmetry between the lengths of surfactant tails. An increase of the basic lamellar thickness with temperature is observed. Microscopic examination reveals characteristic textures of the smectic phase. The thermotropic behavior of sugar-based surfactant, and crown ether-based surfactant metal complexes are investigated, too.

catanionic surfactants; thermal behaviour; phase transitions

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