Infrared study of orientational order parameters of a ferroelectric liquid crystal

Abstract

A method of determining the set of four order parameters S , D , P , and C for a ferroelectric liquid crystal, using complementary results for different sample geometries, is presented. IR measurements have been performed for homeotropic, planar heterogeneous and, planar homogenous sample geometries. Orientational order parameters were determined in two frames of reference to obtain complete information on molecular arrangement. Results for the D , P , and C parameters indicate the importance of both the intrinsic and extrinsic biaxialities. The molecular rotation around the long molecular axis is not free, and the carbonyl dipole and plane of the central phenyl ring are oriented close to the tilt plane. It has been found that transition dipole moments show significant correlations, antiparallel for longitudinal dipoles and parallel for transversal ones.

Recent NMR Studies of Thermotropic Liquid Crystals

“…The equilibrium probability p n is then obtained using Eq. (66). While S is used in calculating the proton T 1 , both S and p n are needed for calculating the spectral densities for each deuteron site.…”

“…prefers to align either more toward X or Y axis. It has been shown both theoretically [64] and experimentally [6,65,66] that P is usually small in a SmC phase.…”

Understanding liquid crystal order parameters deduced from different vibrations in polarised Raman spectroscopy

“…For nematic liquid crystals, the ODF is described in terms of the generalised Legendre polynomials and order parameters where the indices , and take integer values. There are many approaches to measuring the order parameter in liquid crystals including electron spin resonance spectroscopy [1,2], x-ray [3,4,5,6,7,8], optical techniques [9], neutron scattering [10,11], and analysis of infrared spectra [12,13,14] . However, polarized Raman spectroscopy (PRS) is an important optical technique since it can be used to obtain not only the second order term , but also the next higher order term with L = 4, a parameter that can be obtained by very few other experimental methods [3,15,16,17,18,19,20,21,22].…”

Temperature-Dependent Infrared Spectroscopy Studies of a Novel Antiferroelectric Liquid-Crystalline Thiobenzoate

“…Most experiments have been performed for planar sample configuration; however, in the early 2000s, the alternative way of studying the most important order parameters and the molecular tilt angle was proposed. 22,23 Finally, vibrational spectroscopy has become a relevant tool in the studies of de Vries type 24 or biaxial nematic phases. 25−27 As modern quantum chemistry allows us to predict the vibrational spectra with very good accuracy, the experimental data may be nowadays deeply understood and interpreted, giving even further information about the components of the related transition moments, despite the high complexity of the recorded data.…”

“…Since the early works by Kocot et al dealing with order parameters and molecular tilt angle, − many papers presenting successful application of infrared spectroscopy were reported. − In parallel, significant papers by Kim et al − have confirmed the applicability of Raman spectroscopy in related studies and opened the discussion for antiferroelectric liquid crystals. Most experiments have been performed for planar sample configuration; however, in the early 2000s, the alternative way of studying the most important order parameters and the molecular tilt angle was proposed. , Finally, vibrational spectroscopy has become a relevant tool in the studies of de Vries type or biaxial nematic phases. − As modern quantum chemistry allows us to predict the vibrational spectra with very good accuracy, the experimental data may be nowadays deeply understood and interpreted, giving even further information about the components of the related transition moments, despite the high complexity of the recorded data. − …”