International Tables for Crystallography

Scattering from mesomorphic structures
P. S. Pershan. International Tables for Crystallography (2010). Vol. B, ch. 4.4, pp. 547-566  [ doi:10.1107/97809553602060000776 ]


The terms mesomorphic and liquid-crystalline are used synonymously. The order of mesomorphic phases is intermediate between that of liquids and crystals. The progression from the completely symmetric isotropic liquid through the mesomorphic phases into the crystalline phases can be described in terms of three separate types of order. The first kind, molecular orientational order, results from the molecules having some preferential orientation, as found in nematic phases. The second type of order is referred to as bond orientational order and the third kind of order is a positional order of an indefinite lattice of the type that defines the 230 space groups of conventional crystals. For mesomorphic phases with a layered structure, this positional order can be separated into positional order along the layer normal and perpendicular to it, or within the layers. In this chapter, mesomorphic phases are classified according to the different kinds of order present and the scattering from each kind of phase is described. Discotic and other kinds of mesomorphic structures are also discussed.

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About International Tables for Crystallography

International Tables for Crystallography is the definitive resource and reference work for crystallography. The series consists of nine volumes and comprises articles and tables of data relevant to crystallographic research and to applications of crystallographic methods in all sciences concerned with the structure and properties of materials.