Cholesteric liquid crystalline state

Kishi R, Sisido M, Tazuke S (1990) Liquid-crystalline polymer gels. 1. Cross-linking of poly (y-benzyl L-glutamate) in the cholesteric liquid-crystalline state. Macromolecules 23 3779-3784... 

A detailed insight into the freezing-in process is given by optical investigations. As described in 2.3.1.4 for nematics, 2.3.2.3 for cholesterics and 2.3.3.3 for smectics, the optical uniaxial character of the polymers in the liquid crystalline state has been proved by birefringence measurements and the state of order was calculated from these measurements. This method also provides information about the glassy state. For conventional l.c s it has been demonstrated, that the temperature dependence of... 

In an attempt to discern the factor(s) most responsible for ordered solvent induced alterations of reaction rates and specificities, we have investigated the influence of cholesteric liquid-crystalline and other optically active media upon the induction or loss of optical activity in the atropisomers of 1,1 -blnaphthyl (BN, equation 1). We find that optical induction is negligible from thermal (ground-state) lsomerizations (usually <0.1%) but is larger for excited-state lsomerizations conducted in cholesteric mesophases (up to 1.1%). The factors responsible appear to be the geometry and polarizability of the 15N triplet state and rather specific solvent-solute interactions in ordered... 

There have been a lot of studies of cholesteric films and gels in order to exploit their potential as specific optical media and as other functional materials. Most of the preparations were achieved by modification or improvement of previous attempts to immobilize the cholesteric structure of cellulose derivatives into the bulky networks either by crosslinking of cellulosic molecules with functional side-chains in the liquid-crystalline state [203], or by polymerization of monomers as lyotropic solvents for cellulose derivatives [204-206],... 

The recent studies on the structure and properties of polypeptide liquid crystals, which are formed in solution as well as in the solid state, are reviewed in this article. Especially the cholesteric pitch and the cholesteric sense (right-handed or left-handed), which are characteristic factors of cholesteric liquid crystals, are discussed in detail in relation to the effects of temperature, concentration, and solvent. Further cholesteric liquid crystalline structure retained in cast fdms and thermotropic mesomorphic state in some copolypeptides are also discussed. 

Because the molecular forces producing liquid crystalline states are very weak, the structures are easily affected by changes in mechanical stress, electromagnetic fields, temperature, and chemical environment. Three main categories have been recognized smectic, nematic, and cholesteric ... 

Liquid Crystallinity. The liquid-crystalline state is characterized by ori-entationally ordered molecules. The molecules are characteristically rod- or lathe-shaped and can exist in three principal structural arrangements nematic, cholesteric, smectic, and discotic (5,6). 

The book is subdivided into three parts. The first three introductory chapters include consideration of the nature of the liquid crystalline state of matter, the physical properties of mesophases related to their electroop-tical behavior, and the surface phenomena determining the quality of liquid crystal cells giving birth to many new effects. The second part (Chapters 5-7) is devoted to various electrooptical effects in nematic, cholesteric, and smectic mesophases including ferroelectric compounds. Here major emphasis is given to explaining the physical nature of the phenomena. The last part (Chapter 8) is a rather technical one. Here recent applications of liquid crystalline materials in electrooptical devices are discussed. 

Reinitzer discovered liquid crystallinity in 1888 the so-called fourth state of matter.4 Liquid crystalline molecules combine the properties of mobility of liquids and orientational order of crystals. This phenomenon results from the anisotropy in the molecules from which the liquid crystals are built. Different factors may govern this anisotropy, for example, the presence of polar and apolar parts in the molecule, the fact that it contains flexible and rigid parts, or often a combination of both. Liquid crystals may be thermotropic, being a state of matter in between the solid and the liquid phase, or they may be lyotropic, that is, ordering induced by the solvent. In the latter case the solvent usually solvates a certain part of the molecule while the other part of the molecule helps induce aggregation, leading to mesoscopic assemblies. The first thermotropic mesophase discovered was a chiral nematic or cholesteric phase (N )4 named after the fact that it was observed in a cholesterol derivative. In hindsight, one can conclude that this was not the simplest mesophase possible. In fact, this mesophase is chiral, since the molecules are ordered in... 

The phase transitions of cholesteryl nonanoate have been studied with a new apparatus for thermal analytical microscopy. The enantiomer ratio of some chiral sulphoxides can be changed from racemic to a modest preference for one enantiomeric form by dissolution in a cholesteryl ester in its liquid-crystalline ( cholesteric ) state. 5,6-Epoxycholestan-3-yl p-nitrobenzoates exhibit liquid-crystal properties, but 5,6-diols and dibromides are inactive. ... 

The systematic synthesis of non amphiphilic l.c.-side chain polymers and detailed physico-chemical investigations are discussed. The phase behavior and structure ofnematic, cholesteric and smectic polymers are described. Their optical properties and the state of order of cholesteric and nematic polymers are analysed in comparison to conventional low molar mass liquid crystals. The phase transition into the glassy state and optical characterization of the anisotropic glasses having liquid crystalline structures are examined. 

With these properties a wide field of application is revealed As the l.c. side chain polymers can be orientated in the l.c. state by an electric or magnetic field, it is possible to store any information obtained in the l.c. state by cooling the liquid crystalline polymer down to the glassy state. Obvious applications are e.g. optical filters or reflectors, prepared for linearly or circularly polarized light by cholesteric polymers. Furthermore the glassy polymers can serve as anisotropic matrices for dissolved molecules. 

The article covers synthesis, structure and properties of thermotropic liquid-crystalline (LC) polymers with mesogenic side groups. Approaches towards the synthesis of such systems and the conditions for their realization in the LC state are presented, as well as the data revealing the relationship between the molecular structure of an LC polymer and the type of mesophase formed. Specific features of thermotropic LC polymers and copolymers of nematic, smectic and cholesteric types are considered. 

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