Molecular field theory for polar, biaxial bent-core nematics

Abstract

We have studied a polar, biaxial nematic liquid crystal formed from bent-core molecules using molecular field theory. The model includes a simple Heisenberg-form dipolar intermolecular interaction in addition to the usual quadrupolar nematic interaction, and mimics a system consisting of nematogenic bent-core molecules with an large transverse dipole along the bisector of the two molecular arms. Such systems are regarded as good candidates for biaxial nematic liquid crystals. In principle, the molecular dipoles can align, thus stabilizing the ordering of the minor axes. Our calculations predict that, for suitable values of the bent-core interarm angle, the biaxial nematic phase can be stabilized at higher temperatures than in the absence of the transverse dipole. In general, the transverse macroscopic polar order stabilizes the biaxial nematic phase. In particular, for a large enough dipolar interaction, the Landau point in the pure biaxial nematic develops into a line of first-order polar biaxial nematic-to-isotropic phase transitions.

Molecular field theory for biaxial nematics formed from liquid crystal dimers and inhibited by the twist-bend nematic

“…We follow the notation convention of Teixeira et al [39], but with different scaling (see also Dunmur and Luckhurst [40] and Luckhurst [41]). Some of this material can also be found elsewhere [42]. The functions are:…”