On some liquid crystalline phases exhibited by compounds made of bent-core molecules and their mixtures with rod-like molecules

摘要

In most homologous series of compounds made of bent-core (BC) molecules, the B2, B1 and B6 phases occur as the chain length decreases. We have studied binary mixtures of the compound 1,3-phenylene bis[4-(3-methylbenzoyloxy)]4'-e?‘?-dodecylbiphenyl 4'-carboxylate (BC12) which exhibits the B2 phase with the compound 4-biphenylyl 4''-e?‘?-undecyloxybenzoate (BO11) made of rod-like (R) molecules. We ???nd the above sequence of occurrence of the B phases with increasing concentration of BO11. In this paper we describe the physical origin for the formation of these phases in both pure compounds and in the mixtures. We have also found the occurrence of the biaxial smectic A phase when the BO11 concentration is increased to 87a€“95.5 mol%. We also report on another binary system composed of BC12 and 4-e?‘?-octyloxy 4'- cyanobiphenyl (8OCB) made of R molecules. This system exhibits the biaxial smectic A phase down to 30?°C. Using polarized infrared spectroscopy we ???nd that the mutual orientation of the R and BC molecules in the SmAdb liquid crystal is such that the arrow axes of the BC molecules are along the layer normal of the partial bilayer smectic structure formed by the rods. We also describe unusual growth patterns obtained when the nematic phase transforms to the SmAdb phase in a mixture with 24 mol% of BC12.