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

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