X-ray diffraction study of cholesterol-cholesteryl oleate binary mixtures

The phase transitions for binary mixtures of cholesteryl oleate (CO) and cholesterol (CH) have been investigated by X-ray diffraction, differential scanning calorimetry and optical microscopy. The phase diagrams on heating, involving the solid-solid and solid-isotropic liquid transitions, and on cooling, involving the cholesteric and smectic mesophases, have been derived. In particular, a strong supercooling effect of liquid cholesterol and a progressive decrease of the isotropic liquid-cholesteric and cholesteric-smectic transition temperatures were observed. Moreover, some structural modifications induced in the smectic A and in the cholesteric phase by the presence of CH in CO were detected. Finally the dependence of intermolecular distance in the isotropic liquid phase was studied as a function of temperature and mixture composition