Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power

1999 ◽  
Vol 54 (12) ◽  
pp. 747-754 ◽  
Author(s):  
Reiner Memmer ◽  
Folkert Janssen
Keyword(s):  
Liquid Crystalline ◽  
Dopant Concentration ◽  
System Size ◽  
Chiral Molecules ◽  
Cholesteric Phase ◽  
Chiral Induction ◽  
Chiral Liquid Crystal ◽  
Liquid Crystalline Phases ◽  
Helical Twisting Power

Abstract The chiral induction in liquid crystalline phases was studied by Monte Carlo simulation of the chiral Lebwohl-Lasher model. Binary guest-host systems composed of achiral and chiral molecules as well as of different chiral molecules were investigated in dependence on the composition. A cholesteric phase was induced by dissolving a small fraction of chiral molecules in a nematic phase. For dilute solutions the equilibrium pitch was found to be a linear function of the chiral dopant concentration. Independent of system size effects the application of self-determined boundary conditions enabled the determination of the symmetry adapted quantities for the chiral induction, the helical twisting power (HTP) and the achiral helical twisting power (AHTP). Additionally, a different orientational behaviour of enantiomeric dopants in the chiral surroundings of a cholesteric host phase has been determined.

Mixed-dimer formation in binary systems of 4-substituted benzoic acids and structure considerations

2008 ◽  
Vol 86 (6) ◽  
pp. 525-532 ◽  
Author(s):  
Maren Roman ◽  
Annett Kaeding-Koppers ◽  
Peter Zugenmaier
Keyword(s):  
Benzoic Acid ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Binary Systems ◽  
Benzoic Acids ◽  
Dimer Formation ◽  
Crystalline Phases ◽  
Cholesteric Phase ◽  
Liquid Crystalline Phases ◽  
Substituted Benzoic Acids

The phase behavior of binary systems of 4-substituted benzoic acids is governed by the formation of mixed dimers. This study was conducted to determine the effect of the components’ structural difference on mixed-dimer formation in crystalline and liquid-crystalline phases. The phase diagrams of two systems, with 4-[(S)-(–)-2-methylbutoxy]benzoic acid (MBOBA) as one component and 4-(hex-5-enoxy)benzoic acid (HOBA) and 4-(dec-9-enoxy)benzoic acid (DOBA), respectively, as the second component, were determined by differential scanning calorimetry, polarized-light microscopy, and X-ray diffraction. The MBOBA-HOBA system exhibited a cholesteric phase, two solid solutions, and above 58 °C for compositions between 40 and 80 mol% HOBA a crystalline phase of mixed dimers. The MBOBA-DOBA system showed a crystalline phase of mixed dimers at all compositions, a cholesteric phase, and a twisted smectic C phase, which was dominated by mixed dimers at 60 and 70 mol% DOBA. We conclude that liquid-crystalline phases are generally dominated by mixed dimers, but in crystalline phases the formation of mixed dimers is promoted by a greater difference in molecular structure. The crystal structure of two of the pure compounds MBOBA and DOBA and comparable compounds have been determined for an evaluation of the arrangements of the molecules in the crystal and liquid-crystalline state.Key words: benzoic acid, crystal arrangement, phase diagrams, liquid crystal.

scholarly journals Cubic and tetragonal liquid crystal phases composed of non-chiral molecules: Chirality and macroscopic properties

2019 ◽  
Vol 42 (11) ◽  
Author(s):  
Helmut R. Brand ◽  
Harald Pleiner
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystalline ◽  
Triblock Copolymers ◽  
Similar Type ◽  
Chiral Molecules ◽  
Chiral Compounds ◽  
Liquid Crystalline Phases ◽  
Symmetry Properties ◽  
Crystal Phases ◽  
Liquid Crystal Phases

Abstract. We discuss the symmetry properties as well as the macroscopic behavior of the cubic liquid crystal phases showing large chiral domains of either hand in some non-chiral compounds reported recently in the group of Tschierske. These phases are tricontinuous. While they have O or I432 symmetry in each chiral domain, the overall symmetry is $ I m \bar{3} m$Im3¯m as there is no net chirality for compounds composed of non-chiral molecules. It turns out that a rather similar type of phase has also been reported for triblock copolymers. Here we analyze in detail the macroscopic static and dynamic behavior of such phases and we predict, among other results, that they show the analog of static and dissipative Lehmann-type effects in their chiral domains. A description of a cubic liquid crystalline phase of Th symmetry, which has not yet been found experimentally, is also included. Suggestions for experiments are outlined to identify such a phase. In addition, we discuss tetragonal liquid crystalline phases of D4h and D4 (I422) symmetry as they have been reported last year experimentally in connection to the Q phase. Graphical abstract

Synthesis and Characterization of Bowl-Shaped Liquid Crystals with a Core of Calix[6]arene

2011 ◽  
Vol 396-398 ◽  
pp. 2202-2205
Author(s):  
Dan Shu Yao ◽  
Feng Li ◽  
Hao Jie Wang ◽  
Xiao Yun Li ◽  
Mei Tian ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Liquid Crystalline ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Cholesteric Phase ◽  
Chemical Structures ◽  
Liquid Crystalline Phases ◽  
Clearing Temperature ◽  
Mesomorphic Properties

A new kind of bowl-shaped liquid crystals were designed and synthesized by esterification. They used a calix[6]arene as central unit and ω- cholesteric alkyl diacid monoester as mesogenic arms. Their chemical structures were confirmed by FTIR and 1HNMR spectra, their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-Ray Diffraction (XRD) measurements. The results showed that the kind of calix[6]arene bowl-shaped liquid crystals N1-N3 exhibited broad range liquid crystalline phases at moderate temperature, and they displayed cholesteric phase focal-conic texture in liquid crystal states. With increasing the flexibility of monomers M1-M3, the melting point and the clearing temperature decreased in the macromolecules.

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