Notizen: Bestimmung des Helixdrehsinnes cholesterischer Phasen mit der Grandjean-Cano-Methode / Determination of the Helical Sense of Cholesteric Liquid Crystals Using the Grandjean-Cano Method

1977 ◽  
Vol 32 (8) ◽  
pp. 899-902 ◽  
Author(s):  
G. Heppke ◽  
F. Oestreicher
Keyword(s):  
Molecular Structure ◽  
Liquid Crystals ◽  
Nematic Phase ◽  
Ring System ◽  
Cholesteric Liquid Crystals ◽  
Cholesteric Phase ◽  
Chiral Compounds ◽  
Helix Pitch

Abstract A simple way of determining the helix screw sense of a cholesteric phase using the Grandjean-Cano method is described. The helix pitch as well as its sense is investigated for ten cholesteric phases, induced by mesogenic chiral com­pounds in the nematic isomere mixture of 4-methoxy-4′-n-butylazoxybenzene (Nematic Phase 4, Merck). For the chiral compounds with nematic-like molecular structure it is found that the screw sense alternates with the number of bonds between the chiral centre and the ring system.

THE INFLUENCE OF NEW D-SECO-ESTRONE DERIVATIVES ON THE BEHAVIOR OF THE CHOLESTERIC LIQUID CRYSTALS BINARY MIXTURES

2006 ◽  
Vol 20 (21) ◽  
pp. 2999-3013 ◽  
Author(s):  
D. Ž. OBADOVIĆ ◽  
M. STOJANOVI ◽  
S. JOVANOVIĆ-ŠANTA ◽  
D. LAZAR ◽  
A. VAJDA ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Binary Mixtures ◽  
Average Distance ◽  
Molecular Mechanic ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
Cholesteric Liquid Crystals ◽  
Cholesteric Phase ◽  
Molecular Length

We have studied the influence of the new chiral non-mesogenic seco-estrone derivatives 1-7, synthesized in several synthetic steps starting from estrone, onto the physical characteristics of the binary mixtures of cholesteric liquid crystals. We have examined the phase transitions of the mixture of cholesteryl laurate and cholesteryl enantate with the added chiral non-mesogenic additives 1-7 (45%-45%-10%; Mix.1-Mix.7, respectively). A considerable shift of the I → Ch phase transition temperature, as well as of the temperature of the SmA * phase formation, was observed. X-ray diffraction data enabled the determination of the molecular structures of the compounds 3, 5, 6 and 7, the crystal lattice parameters of the new chiral additives and their molecular length (ℓ) and width (d*), as well as some parameters of the mixtures Mix.1-Mix.6: the thickness of smectic layers and the longitudinal spacing distance in the cholesteric phase (d) and the average distance between the long axes of neighbouring molecules (D). Using molecular-mechanic calculations, on the basis of solved molecular structures, the most probably conformation of the other compounds (1, 2 and 4) used in this work is determined. We have also investigated the influence of these chiral additives onto the pitch of the cholesteric helix of a binary mixture of cholesteric liquid crystals.

Rotatable Diffraction Gratings Based on Cholesteric Liquid Crystals with Phototunable Helix Pitch

2015 ◽  
Vol 3 (9) ◽  
pp. 1273-1279 ◽  
Author(s):  
Alexander Ryabchun ◽  
Alexey Bobrovsky ◽  
Joachim Stumpe ◽  
Valery Shibaev
Keyword(s):  
Liquid Crystals ◽  
Diffraction Gratings ◽  
Cholesteric Liquid Crystals ◽  
Helix Pitch

Temperaturfunktionen der durch Mehrfachdotierung mit chiralen Verbindungen in einer nematischen Phase induzierten Helixganghöhe / Temperature Dependence of the Induced Helical Pitch of a Nematic Phase Using Several Chiral Additives

1979 ◽  
Vol 34 (5) ◽  
pp. 594-599
Author(s):  
A. Göbl-Wunsch ◽  
G. Heppke
Keyword(s):  
Temperature Dependence ◽  
Nematic Phase ◽  
Temperature Behaviour ◽  
Helical Pitch ◽  
Chiral Compounds ◽  
Helix Pitch ◽  
Helix Structure ◽  
Nematic Phases ◽  
Good Agreement

Abstract A helix structure can be induced in nematic phases by adding chiral compounds. In general the helix pitch increases with temperature. It is shown that by using two suitable doping agents, each of which would give different senses of helix rotation when used individually, a particular temperature behaviour can be obtained. Depending on the concentrations, a temperature independent pitch, for example, or a helix inversion can be achieved. The results of experiments using the nematic phase N 4 (Merck) show good agreement with the theoretically predicted temperature dependence of the pitch.

scholarly journals Statistical Theory of Elastic Constants of Cholesteric Liquid Crystals

2002 ◽  
Vol 57 (3-4) ◽  
pp. 105-118 ◽  
Author(s):  
Andrzej Kapanowski
Keyword(s):  
Statistical Theory ◽  
Liquid Crystals ◽  
Elastic Constants ◽  
Binary Systems ◽  
Cholesteric Liquid Crystals ◽  
Cholesteric Phase ◽  
Small Density ◽  
Nematic Phases ◽  
The Stability ◽  
The One

A statistical theory of cholesteric liquid crystals composed of short rigid biaxial molecules is presented. It is derived in the thermodynamic limit at a small density and a small twist. The uniaxial (biaxial) cholesteric phase is regarded as a distorted form of the uniaxial (biaxial) nematic phase. The chirality of the interactions and the implementation of the inversion to the rotation matrix elements are discussed in detail. General microscopic expressions for the elastic constants are derived. The expressions involve the one-particle distribution function and the potential energy of two-body short-range interactions. It is shown that the elastic constants determine the twist of the phase. The stability condition for the cholesteric and nematic phases is presented. The theory is used to study unary and binary systems. The temperature and concentration dependence of the order parameters, the elastic constants and the twist of the phase are obtained. The possibility of phase separation is not investigated.

Automated determination of n-cyanobiphenyl and n-cyanobiphenyl binary mixtures elastic constants in the nematic phase from molecular simulation

2020 ◽  
Vol 5 (6) ◽  
pp. 1131-1136
Author(s):  
Jiale Shi ◽  
Hythem Sidky ◽  
Jonathan K. Whitmer
Keyword(s):  
Liquid Crystals ◽  
Molecular Simulation ◽  
Elastic Properties ◽  
Binary Mixtures ◽  
Elastic Constants ◽  
Nematic Phase ◽  
New Techniques ◽  
New Applications ◽  
Automated Determination

This work explores new techniques in molecular simulation which can be used to precisely determine and engineer elastic properties of liquid crystals for new applications.

Oll the Odd-Even Effect in the Helix of Non-Sterol Cholesterogens

1979 ◽  
Vol 34 (11) ◽  
pp. 1359-1361
Author(s):  
B. W. van der Meer ◽  
G. Vertogen
Keyword(s):  
Molecular Structure ◽  
Ring System ◽  
Chiral Compounds

A model is proposed to explain the alternation of the screw-sense of the helix with the number of bonds between the chiral centre and the ring system in chiral compounds with nematic-like molecular structure

Torsional Shear Flow of Nematic and Cholesteric Liquid Crystals. Part I: Nematic Phase

1979 ◽  
Vol 34 (7) ◽  
pp. 818-831 ◽  
Author(s):  
J. Wahl
Keyword(s):  
Liquid Crystals ◽  
Shear Flow ◽  
Electric Field ◽  
Simple Shear ◽  
Nematic Phase ◽  
Simple Shear Flow ◽  
Cholesteric Liquid Crystals ◽  
Material Constants ◽  
Torsional Shear

The simple shear flow of a homeotropic nematic layer in an electric field normal to the layer is studied theoretically and experimentally. Several material constants of MBBA are determined as a function of temperature.

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