Optical textures in TGBA mesophases

In this paper, we present the results of polarized optical microscopy obser vations performed on different series of compounds exhibiting twist grain b oundary mesophases (TGB). From all the compounds investigated, it appears t here are two main typical optical textures which characterize TGBA mesophas es in general. One type of texture is characteristic of a planar helical st ructure, while the other is a cylindrical (or marginally cone-like) domain texture, resembling the developable domains observed in columnar systems. M oreover, both textures can coexist in the same sample over the whole temper ature range of the TGB phases. The detection, at the same temperature, of t hese two types of textures could then be considered as one of the signature s of the TGBA mesophases.