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.
Source:
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
1994))
on page 584
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
