Term: liquid-crystal transitions
https://doi.org/10.1351/goldbook.L03579

Definition:
A liquid crystal is a molecular crystal with properties that are both solid- and liquid-like. Liquid crystals are composed predominantly of rod-like or disc-like molecules, that can exhibit one or more different, ordered fluid phases as well as the isotropic fluid; the translational order is wholly or partially destroyed but a considerable degree of orientational order is retained on passing from the crystalline to the liquid phase in a mesomorphic transition.  Transition to a nematic phase. A mesomorphic transition that occurs when a molecular crystal is heated to form a nematic phase in which the mean direction of the molecules is parallel or antiparallel to an axis known as the director.  Transition to a cholesteric phase. A mesomorphic transition that occurs when a molecular crystal is heated to form a cholesteric phase in which there is simply a spiralling of the local orientational order perpendicular to the long axes of the molecules.  Transition to a smectic state. A mesomorphic transition that occurs when a molecular crystal is heated to yield a smectic state in which there is a one-dimensional density wave which produces very soft/disordered layers.  

Related Terms:
1) liquid crystal (http://doi.org/10.1351/goldbook.LT06856).
2) isotropic (http://doi.org/10.1351/goldbook.I03353).
3) mesomorphic transition (http://doi.org/10.1351/goldbook.M03847).
4) smectic state (http://doi.org/10.1351/goldbook.S05714).

Source: PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 584 (https://doi.org/10.1351/pac199466030577)

Citation: 'liquid-crystal transitions' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.L03579

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