OPTICAL INVESTIGATIONS ON A LIQUID-CRYSTALLINE SIDE-CHAIN POLYMER WITH BIAXIAL NEMATIC AND BIAXIAL SMECTIC-A PHASE

A liquid-crystalline side-chain polymer with laterally incorporated naphthalene groups in the mesogenic moiety is investigated in binary mixtures with an optical uniaxial low-molar-mass liquid crystal. Mixtures with up to 50 mol-% content of the monomeric liquid crystal show a biaxial nematic phase. At lower temperatures a new biaxial smectic phase is observed, which corresponds to the smectic A phase. The angles between the optical axes are measured in dependence of temperature and mixture composition. Starting from the neat polymer, the angles decrease in the nematic as well as in the smectic phase with increasing mole fraction of the uniaxial liquid crystal. From the results a phase transformation uniaxial nematic to biaxial nematic can be inferred.