Thermotropic liquid crystals translational order

Liquid crystal phases, or mesophases, are characterized by a partial order, intermediate between the full orientational and translational disorder of the isotropic liquid phase and the full orientational and translational order of the crystalline phase. Thermotropic liquid-crystal phases are obtained for a given compound (or possibly a mixture) as a function of temperature, while the so-called lyotropic liquid-crystal phases are obtained as a function of the concentration of a given solute in a solvent Typical examples of the latter systems are the various types of aggregates formed by amphiphilic molecules either in water or in organic solvents. In this chapter we will be interested only in thermotropic systems. An interesting review on lyotropic ionic liquid crystals can be found in Ref. [2],... 

Thermotropic liquid crystal Substance showing one or more liquid phases appearing as a function of temperature between the solid and the isotropic liquid, in which the constituent molecules show partial orientational ordering and possible partial translational order. 

The simplest structure with translational order is a one-dimensional layered structure (Fig. 1.2). In thermotropic liquid crystals, there are a number of such smectic phases formed by molecules in a weakly layered arrangement (Section 5.2.2). Amphiphiles also form smectic phases, but they are usually... 

The difference between direct ordering of molecules and the indirect ordering of molecules via supermolecular aggregates is one of the distinctions between different types of soft material. Thermotropic liquid crystal phases result from partial orientational and translational order of the molecules. In contrast, the symmetry of lamellar, micellar and bicontinuous phases is specified by the location of supermolecular aggregates. The molecules within the aggregate do not have the same orientational and translational order as the mesoscopic structure itself in fact, they can be relatively disordered . 

Thermotropic liquid crystal phases are formed by anisotropic molecules with long-range orientational order, and in many types of structure some degree of translational order. The main types of mesogens are those that are rod-like or calamitic and those that are disc-like or discotic. 

All thermotropic liquid crystal phases are characterized by long-range orientational order of the mesogens. However, the extent of translational order... 

Mesogens are compounds which generate mesophases, intermediate between the crystal phase and the liquid or solution phase. Mesophases possess some of the order of crystals, but are fluid like liquids. There are different classes of mesophases, principally thermotropic where temperature is the principal variable in phase changes and lyotropic where there is additional solvent and concentration is an important variable. The different classes of thermotropic phases relate to the different types of partial ordering of the molecules in nematic phases there is orientational order of the molecules, and in smectic phases there is translational order. 

Features of liquid crystallinity (both lyo- and thermotropic) are also to be found in exclusively inorganic systems. For example, metal carbonates can be crystallized in gels to form dense pm-sized aggregates of many crystallites that are themselves orientationally ordered, and devoid of any translational ordering. So, while the material is (micro)crystalline, its mesostructure on the pm scale deserves to be recognized as liquid crystalline. 

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