Study of Phase Transitions Involving the Mesophases of Cholesteryl Linoleate

Abstract

An investigation of the structural properties of cholesteryl linoleate was performed by using several techniques. In particular, the following phase transitions occurring in the cholesteryl linoleate were investigated by X-ray diffraction, DSC and polarizing microscopy: solid-isotropic liquid, isotropic liquid-cholesteric, cholesteric-smectic. This study follows a previous similar one on the cholesteryl oleate. Both these substances are interesting for their peculiar physical properties and biological implications. As in the case of cholesteryl oleate the smectic phase appears to be S_A. The structural properties of cholesteryl linoleate appear to be similar to those of cholesteryl oleate as expected; in spite of some observed differences which should be attributed to the presence of two double bonds in the cholesteryl linoleate instead of a single one in the cholesteryl oleate. A phase coexistence was observed during the solid-isotropic liquid phase transition. Strong pretransitional effects were observed at the cholesteric-smectic phase transition. In particular, the longitudinal coherence length ξ_|| appears to diverge as the critical temperature is approached in the cholesteric phase by cooling the sample.