Also contains definitions of: cholesteric phase, nematic phase
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
- 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
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
on page 584