OPTICAL INVESTIGATIONS IN THE VARIOUS PHASES OF AN ANTIFERROELECTRIC LIQUID-CRYSTAL

We report detailed results of optical rotatory power (ORP), slective reflection (SR), refractive index anisotropy (RIA), and anisotropic Rayleigh scattering (ARS) measurements in the antiferroelectric liquid crystal, 4-(1-methylheptyl-oxycarbonyl) phenyl-4'-octyloxy phenyl-4-carboxylate (MHPOBC). The ORP in Sm-A and Sm-C*(a) phases has been found to be zero or at least very weak compared to ordinary liquids with strongly chiral molecules. No helical pitch is observed in the Sm-A, Sm-C*(a) and Sm-C*(g)amma phases in the range 200-2200 nm. The combined use of ORP and SR allows the precise determination of the tilt angle of the smectic-C phases. Obtained values are found to be in good agreement with both theoretical calculations and experimental results obtained from RIA. Moreover, ARS reveals the local biaxial character of the Sm-C*(A) phase, while the absence of critical behavior of the Sm-A <-- Sm-C*(a) phase transition is a direct proof of the lack of biaxiality in the Sm-C*(a) phase.