Eur. Phys. J. E (2014) 37: 79
https://doi.org/10.1140/epje/i2014-14079-0

Regular Article

Molecular theory of proper ferroelectricity in bent-core liquid crystals

¹ Department of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, Richmond Street, Glasgow, Scotland, UK
² Faculty of Physics, Mathematics and Computer Science, Tadeusz Kościuszko Cracow University of Technology, Podchora̧żych 1, Kraków, Poland

^* e-mail: grzegorz@th.if.uj.edu.pl

Received: 2 May 2014
Revised: 4 August 2014
Accepted: 6 August 2014
Published online: 12 September 2014

Abstract

Antiferro- and ferro-electric ordering has been discovered in orthogonal smectic phases composed of nonchiral bent-core molecules. These systems are the only proper fluid ferroelectrics confirmed experimentally so far. We consider a molecular theory of proper ferroelectric ordering in isotropic, nematic and smectic A phases and conclude that the delicate balance between the tendencies for local parallel and antiparallel ordering of molecular electric and steric dipoles is strongly shifted in restricted geometries. This is a reason why dipolar ordering is more likely to occur within a smectic layer. We derive model interaction potentials for polar bent-core molecules and present the results of the mean-field theory of ferroelectric ordering in the orthogonal smectic phase taking into account also the molecular biaxiality. Order parameter profiles have been calculated numerically and phase diagrams are presented which enable one to analyze the relative importance of dipole-dipole interaction and intermolecular attraction modulated by polar bent-core molecular shape.