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 a 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 stabilising 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 stabilised at higher temperatures than in the absence of the transverse dipole. In general, the transverse macroscopic polar order stabilises 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.

Graphical Abstract

KEYWORDS:

• Biaxial nematics
• polar nematics
• molecular field theory
• bent-core nematics
• V-shaped molecules

Acknowledgements

TBTT acknowledges financial support from the School of Mathematical Sciences, University of Southampton, through a School Ph.D. Studentship. TBTT thanks Prof. E.G. Virga for a helpful discussion. The final parts of this research were carried out while TJS and TBTT were participants in the ‘Mathematics of Liquid Crystals’ programme at the Isaac Newton Institute for Mathematical Sciences, University of Cambridge (January-July 2013). They thank the organisers of this programme for the invitation to participate, and the Director of the Institute for his hospitality during the course of the programme.

Disclosure statement

No potential conflict of interest was reported by the authors.