Liquid crystals are a class of molecules that, under some conditions inhabit a phase in which they exhibit isotropic, fluid-like behavior – that is, with little long-range ordering – but which under other conditions inhabit one or more phases with significant anisotropic structure and long-range ordering, but still with an ability to flow.
Liquid crystals find wide use in liquid crystal displays, which rely on the optical properties of certain liquid crystalline molecules in the presence or absence of an electric field. In the presence of electric field, these molecules align with electric field, altering polarization of the light in a certain way.
The ordering of liquid crystalline phases is extensive on the molecular scale, but does not extend to the macroscopic scale as might be found in classical crystalline solids. The ordering in a liquid crystal might extend along one dimension, but along another dimension, might have significant disorder.
Important types of liquid crystals include
- nematics (most nematics are uniaxial but biaxial nematics are also known)
- smectics (smectic A, smectic C, and hexatic)
- columnar phases
- de Gennes, P.G. and Prost, J. The Physics of Liquid Crystals, Claredon Press (1993).