Investigation of the Cholesteryl Oleate Mesophases by X-Ray Diffraction

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Abstract
The following phase transitions occurring in the cholesteryl oleate were investigated by X-ray diffraction: solid-isotropic liquid, isotropic liquid-cholesteric, cholesteric-smectic. The sample purity was 98%. Strong pretransitional effects were observed at the solid-isotropic liquid phase transition and at the cholesteric-smectic phase transition. At this last transition the longitudinal coherence length ξ∥ appears to diverge as the critical temperature is approached in the cholesteric phase, whereas the transversal coherence length ξτ increases at the critical temperature in the smectic phase in an abrupt way. It seems from the temperature dependence analysis of the angular position of the low angle peak that the smectic phase is a smectic A phase and that a progressive melting of chains occurs at the temperature increases.