A nematic-polar columnar phase sequence in new bent-shaped liquid crystals based on a 7-hydroxynaphthalene-2-carboxylic acid core

Abstract

Mesomorphic properties of new bent-shaped liquid crystals based on 7-hydroxynaphthalene-2-carboxylic acid are presented. The central unit of the molecular core was also modified by substitution of the chlorine atom or methyl group. Texture and calorimetric studies, as well as electrooptical, X-ray and dielectric measurements of selected compounds were performed. For long homologues the lamellar B₂ phase was observed, while for shorter homologues two-dimensional columnar phases were found, built of layer fragments with the electron density modulation plane perpendicular to polarization direction. Based on X-ray patterns, two types of modulated polar columnar phases were distinguished, having oblique or orthogonal centred crystallographic unit cells and differing in relative position of the neighbouring layer fragments. For some homologues above these phases the nematic phase was also formed.