Classification chiral nematics

J. Bezic and S. Zumer, Chiral nematic liquid crystals in cylindrical cavities A classification of planar structures and models of nonsingular disclination lines, Liq. Cryst. 14, 1695 (1993). 

The orthogonal arrangement of the disc-like molecules in the columns of and D id phases makes these phases uniaxial, while the tilted phases (Drd and Doh.d and Dt) are optically biaxial. There are two additional columnar phases labeled as and that have not yet been classified. The columnar phases were discovered before the observation of a nematic phase for disc-like molecules. Both chiral nematic phases and the re-entrant behavior have now been observed in discotics. The phase diagram and molecular structure of a typical discotic liquid crystal are shown in Fig. 1.11. Finally, it is noted that another classification scheme for the discotic mesophases has been used [1.26], which is based on the notation used for the conventional smectics. 

In addition to containing a wealth of information on microscopic techniques and materials, Friedel s article represented in 1922 the first classification of liquid crystals into types, i.e., nematic, smectic and cholesteric. Today, of course, cholesterics are known simply as chiral nematics with no need that they be derived from cholesterol, and we recognize the existence of several polymorphic smectic forms, whereas Frie-del allowed for only one (today s smectic A SmA). 

Classification of Chiral Nematic Liquid Crystalline Compounds.307... 

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