Biaxial order parameter in the homologous series of orthogonal bent-core smectic liquid crystals

Abstract

This version is available at https://strathprints.strath.ac.uk/47177/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.PHYSICAL REVIEW E 88, 012504 (2013) Biaxial order parameter in the homologous series of orthogonal bent-core smectic liquid crystals The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter (S) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: S for the long axes and C for the ordering of the short axes of molecules. The temperature dependencies of S and C are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-AP A ) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both S and C, particularly the temperature dependency of the latter, are being experimentally determined. Results show that S in the orthogonal smectic phase composed of bent cores is higher than in Sm-A calamatic LCs and C is also significantly large.

Molecular theory of proper ferroelectricity in bent-core liquid crystals

“…As observed in ref. [13], the spontaneous polarization in the ferroelectric bent-core smectic phase appears to be very large which is consistent with large values of the orientational order parameter reported very recently in [14].…”

“…One notes that the ferroelectric ordering in orthogonal bent-core smectic phases, which has recently been observed experimentally, is further stabilized by the high orientational order of long molecular axes (see a recent paper [14] where high values of the nematic order parameter have been measured). In the case of high nematic order of long molecular axes the transverse dipoles of bent-core molecules are restricted to the plane of the smectic layer.…”

Occurrence of Five Different Orthogonal Smectic Phases in a Bent-Core (BC) Liquid Crystal

“…Here we report a new BC material with symmetric terminal chain lengths which exhibits a phase sequence of three different polar orthogonal smectic phases (Sm-AP A , Sm-AP AR and Sm-AP R ) in addition to optically biaxial non-polar Sm-A b on cooling down from the optically uniaxial Sm-A. Occurrence of these phases was confirmed by biaxiality measurements [20][21][22][23], second harmonic electro-optic response [23] and dielectric spectroscopy [24]. It is obviously of enormous to significance to find the five different mesophases at relatively lower temperature region in a low molar pure BC compound having a highly polar cyano group attached to the middle of the core.…”

Observation of an anomalous SmA-SmC-SmA phase sequence in a bent-core liquid crystal derived from 4-cyanoresorcinol

“…The common characteristics of these phases are (a) constituent molecules are achiral but (b) they possess long-range in-layer polarization and biaxiality, and these arise from the C 2v symmetry. The temperature dependences of both primary and secondary (i.e., biaxial) order parameters in orthogonal BC phases were studied earlier [9,10]. The characteristics and the structures of the bent-core LC systems have been reviewed [11,12].…”

“…Table S1 in the Supplemental Material [27] gives an overview of our present understanding of the phase sequence of 1/16. When cooling from the isotropic state, it transforms to an orthogonal SmAlike phase [9,10,12] at higher temperatures with a series of paraelectric (SmCP R ) and polar tilted (B2-like) SmC phases (SmC S P hel F , SmC A P A ) exhibited at lower temperatures [34,36]. The most fascinating feature of these long chain compounds is the formation of a heliconical phase designated as SmC S P hel F , identified first by the observation of a helical structure in planar-aligned samples of 1/16 and 1/18, by AFM of 1/16 [34], and these were unambiguously confirmed in 1/14 by soft resonant x-ray scattering [35].…”