Induction of chirality in nematic phases

Abstract

2014 Des dispositifs de visualisation ou d'affichage à cristaux liquides utilisent les propriétés électrooptiques ou thermotropiques particulières à la phase cholestérique quand le pas de son hélice est de l'ordre de la longueur d'onde de la lumière et quelques micromètres. Les composés les plus connus présentant naturellement cette phase avec des pas appropriés sont les esters de cholestérol; malheureusement ces corps ne sont pas très stables chimiquement. Des nématiques stables tordus, soit par mélange avec un composé chiral, soit par adjonction d'un radical chiral permettent aussi de réaliser cette phase. Dans ce cas le pas dépend d'un grand nombre de facteurs. Cet article rassemble les prédictions théoriques sur l'influence des concentrations, de la température ou du radical adjoint sur le pas et les confronte à un ensemble très complet de résultats expérimentaux originaux ou déjà connus.Abstract. 2014 Some electrooptic and thermooptic effects of cholesteric phase are used in liquid crystal visualisation and display systems provided spiral pitch is equal to a visible wavelength or several micrometers. Liquid crystals with cholesteric properties were generally cholesteric esters. Unfortunately these materials are chemically nonstable. More stable nematic liquid crystals twisted by mixing with chiral materials or by adding assimetric side chain have also cholesteric phase. In this case spiral pitch depends on many factors. This report unites theoretically predicted temperature and concentration dependence of pitch and compares it with some original or known results. Revue Phys. Appl. 16 (1981) 193-208' ' MAI 1981, Classification Physics Abstracts 61.30

Through-space transfer of chiral information mediated by a plasmonic nanomaterial

“…Furthermore, we show that chirality is induced into the achiral plasmonic surface of the substrate by enantiomeric analytes. This is a new phenomenon of chirality induction that is fundamentally different to previously reported mechanisms [23][24][25][26][27][28][29] . We observe a symmetry breaking of surface plasmons interacting with a resonant dye molecule once they are tethered to chiral molecules.…”

Liquid crystal bubbles forming a tunable micro-lenses array

“…The cholesteric pitch was determined by the concentration c, of the chiral agent: p ¼ 1/(HTPÁc), where HTP is the helical twisting power of the chiral agent. 24 The cells were assembled so to obtain a confinement ratio C ¼ d/p % 1. All direct optical observations were carried out at room temperature by using a polarizing optical microscope in conjunction with a CCD camera.…”

Cholesteric Liquid Crystal Mixtures Sensitive to Different Ranges of Solar UV Irradiation

“…In the case of the cholesterics, as our experiments showed, the phototransformation of the molecules, together with the ''nematic monolayers'' [19][20][21] parameters, changes as well the supramolecular parameter -the helix pitch. The helical twisting power of induced cholesterics depends on the characteristics of both components: the optically active dopant and the nematic host [19][20][21].…”

“…The helical twisting power of induced cholesterics depends on the characteristics of both components: the optically active dopant and the nematic host [19][20][21]. Thus, the experimentally observed decrease of the pitch in the case of the photoisomerizable nematic host is connected not only with the lowering in concentration of the nematogenic trans-isomer FIGURE 12 Absorption spectrum for a mixture with 99% of an UV transparent nematic and 1% of the photoisomerizable ZLI-811.…”