Growth of toric domains in the smectic phase of oxadiazoles

In a previous paper (Phase Transitions, 80(9), 987, 2007) we discussed the smectic and nematic textures of some mesomorphic oxadiazole compounds with terminal Cl-substituent. Optical microscope investigations showed a very interesting behaviour of smectic and nematic phases; the smectic phase has fan-shaped and toric textures and the nematic phase has spherulitic domains, which disappear as the sample is further heated, the texture changing into a smooth one. Here, we investigate four oxadiazole compounds with the same structure but terminal Br-substituent. The behaviour of the smectic and nematic phases is like that observed in the compounds with Cl. The focus of the paper is on the growth of toric domains from the nematic melt and on the role of defects in the domain structure.