Macroscopic description of the isotropic to antiferroelectric B2 phase transition in banana-shaped liquid crystals

摘要

We present a mean-field description of the phase transitions, which are obtained when cooling from the isotropic liquid to the first liquid crystalline phase in compounds composed of achiral banana-shaped molecules. We put special emphasis on the isotropic to antiferroelectric B2 phase transition. The free energy is written in terms of the coupled order parameters including the antiferroelectric polarization. We present a detailed analysis of the different phases that can occur and analyze the question under which conditions a direct isotropic to antiferroelectric B2 phase transition is possible when compared with other phase transitions. The theoretical results are found to be in qualitative agreement with all published experimental results.