PRESSURE-DEPENDENCE OF OPTICAL-ACTIVITY IN THE ISOTROPIC-PHASE OF A CHIRAL LIQUID-CRYSTAL

Optical activity measurements in the isotropic liquid phase of cholesteryl oleyl carbonate just above the liquid-crystal transition pressure were performed for various temperatures up to 200 MPa. The observed optical activity exceeds the molecular activity and can be explained as a pretransitional phenomenon. The maximum value, which the optical activity reaches as the transition to the liquid-crystal phase is approached, first decreases then increases when clearing temperature and pressure are raised. A theoretical relationship between the pretransitional optical activity and two structural modes is used to interpret this unusual behaviour.