Liquid Crystals Their Structures and Physical Properties

Chandrasekhar S 1998 Columnar, discotic, nematic and lamellar liquid crystals Their structures and physical properties Handbook of Liquid Crystals Vol 2B. Low Molecular Weight Liquid Crystals I ed D Demus, J Goodby, G W Gray, H-W Spiess and V Vill (New York Wiley-VCH)... 

Chapter VIII Discotic Liquid Crystals Their Structures and Physical Properties. . . 749 S. Chandrasekhar... 

Thennotropic and lyotropic liquid crystals share a common state of matter with many analogies in their structural and physical properties. However, these two fields of liquid crystal research are usually treated completely separately. This is partially due to historical reasons, but also to striking differences in some aspects of these two classes of liquid crystals. One of these differences is the occurrence of thermotropic phases which do not have a lyotropic counterpart A compelling example of this is the thermotropic ferroelectric SmC phase. Due to its unique chirality effects, i.e. ferroelectricity and a helical configuration of the tilt-direction, this phase attracted considerable scientific interest over the last decades. However, there are no reports found in literature about a SmC analog phase in lyotropic liquid crystals. 

Sect. 2.5. General discussions of the classical phases and their transitions can be found in your favorite physics, chemistry, or physical chemistry text. Liquid crystals are treated by DeGennes PG (1974) The Physics of Liquid Crystals. Clarendon Press, Oxford Brown GH (1975) Advances in Liquid Crystals. Academic Press, New York Gray GW (1962) Molecular Structure and the Properties of Liquid Crystals. Academic Press, New York. Plastic crystals by Sherwood N, ed. (1979) The Plastically Crystalline State (Orientationally-disordered Crystals). Wiley, Chichester. For the condis state see Wunderlich B,MollerM,Grebowicz J, Baur H (1988) Conformational Motion and Disorder in Low and High Molecular Mass Crystals. Springer Verlag, Berlin (Adv Polymer Sci Vol 87). 

The Liquid Crystals book series publishes authoritative accounts of all aspects of the field, ranging from the basic fundamentals to the forefront of research from the physics of hquid crystals to their chemical and biological properties and, from their self-assembhng structures to their applications in devices. The series will provide readers new to liquid crystals with a firm grounding in the subject, while experienced scientists and liquid crystallographers will find that the series is an indispensable resource. 

The existence of such building blocks or fragments is a fundamental principle in experimental structural and physical chemistry [7]. For example, individual molecules carry well-defined spectroscopical and structural properties. These properties are essentially preserved although they are more-or-less influenced by the various chemical environments in crystalline phase, in a liquid, or in different solutions. This feature that a considerable number of molecular properties remain practically the same in quite different circumstances, is called transferability [8]. The transferability of molecular properties is associated with the weakness of the intermolecular forces as compared to the intramolecular interactions, which govern these molecular properties. Molecules are very suitable building blocks of the matter provided their size does not exceed a certain limit. Small molecules may be considered as building blocks in molecular crystals, liquids, solutions and in general in various condensed phase systems. 

The properties of materials are consequences of their structures at the molecular level. Solids are the mainstays of technology, and it is hardly surprising that so much effort has gone into the development and understanding of their properties. We dealt with their electrical properties in Sections 3.13 and 3.14. Here we explore some of their other physical properties as well as the properties of the much softer materials known as liquid crystals. 

We briefly discussed the origin and structure of liquid crystals in Section 4.13. The last decade has witnessed a surge of interest in liquid crystals because of their applications in display devices (devices that convert an electrical signal into visual information). The design of liquid crystal (LC) devices relies on the relation between the molecular structure and the phase behaviour (relative smectic-nematic tendency, NI etc.) as well as the physical properties of the liquid crystals (Chandrasekhar, 1994). 

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