liquid crystal

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liquid crystal,

liquid whose component particles, atoms or molecules, tend to arrange themselves with a degree of order far exceeding that found in ordinary liquids and approaching that of solid crystals. As a result, liquid crystals have many of the optical properties of solid crystals. Moreover, because its atomic or molecular order is not as firmly fixed as that of a solid crystal, a liquid can be easily modified by electromagnetic radiation, mechanical stress, or temperature, with corresponding changes in its optical properties. In typical early uses, a small electrical impulse darkened the crystal so that it was clearly visible against the lighter background of neutral crystals. An array of seven lozenges, each of which can be darkened by a separate impulse, can yield any digit. Such liquid crystal displays (LCDs) have become the most common means of producing visual readouts on such devices as digital clocks and electronic calculators. Color LCD panels consisting of millions of pixels, or picture elements, each containing three subpixels (one each for red, blue, or green, with the color produced by a filter), are used as viewing screens in television sets, computer monitors, and other devices; the light source in LCD panels is now typically an LED backlight. LCDs have significantly lower energy requirements than the cathode-ray tubescathode-ray tube
(CRT), special-purpose electron tube in which electrons are accelerated by high-voltage anodes, formed into a beam by focusing electrodes, and projected toward a phosphorescent screen that forms one face of the tube.
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 formerly used in television sets and computer monitors. Some liquid crystals vary the color of the light that they reflect as their temperature changes. Since the colors reflected at any given temperature are quite specific, temperature can be measured by this means to an accuracy of 0.1°C;.

Bibliography

See D. Dunmur and T. Sluckin, Soap, Science, and Flat-Screen TVs (2011).

liquid crystal

[′lik·wəd ′krist·əl]
(physical chemistry)
A liquid which is not isotropic; it is birefringent and exhibits interference patterns in polarized light; this behavior results from the orientation of molecules parallel to each other in large clusters.

liquid crystal

A liquid crystal is a state of matter between liquid and solid (a "mesophase"). They change shape like a fluid but have the molecular alignment characteristics of a solid crystal. Liquid crystals are composed of organic, rod-shaped molecules that align in parallel, and the common types used in electronic displays are nematic, cholesteric and smectic. See LCD, LCD types and LCD categories.

Nematic LCs
Randomly positioned in parallel, nematic LCs react quickly to electric fields, which is why they are used in the great majority of LCD screens. Meaning "thread" in Greek, nematic LCs are monostable and return to their original alignment when the electric field is removed.

Cholesteric LCs (Chiral Nematic LCs)
Cholesteric LCs are lined up in separate layers that form a spiral (helix). The displays retain their image without power (bistable) but are slower to react to changes than nematic screens. See cholesteric LCD.

Smectic LCs
Positioned side-by-side in layers, smectic LCs are bistable with similar attributes as cholesteric LCs. They retain their image without power and are slower to react than nematics. Smectic means "soapy" in Greek.

Discovered in the 19th Century
In 1888, liquid crystals were identified by Austrian botanist Friedrich Reinitzer and German physicist Otto Lehmann. Studying the cholesterol in carrots using a temperature-controlled polarizing microscope, they noticed that the light passing through the carrot compound (later known as "cholesteryl benzoate") exhibited the refraction effect of a solid crystal when heat was applied. By 1907, Germany-based Merck was selling "liquid and flowing crystal" chemicals.
References in periodicals archive ?
k is the bending rigidity, H is the mean curvature, [K.sub.A] is the nematic elastic constant (elastic isotropy approximation), [n.sup.y] represent the components of the director field and g is the metric tensor.
Azimuthal scans were fit to a bimodal Gaussian function, capable of capturing the shapes of the nematic peaks (20), (38).
General expressions for the nematic configuration considering all these phenomena have been recently obtained for a nematic slab under arbitrary boundary conditions [31].
Because of the fact that the fundamental hydrodynamics of the nematic director and rigid rods are identical (Eq.
Zannoni, "Nematics with quenched disorder: how long will it take to heal?" Physical Review Letters, vol.
1, depending on the relative magnitudes of the three elastic constants [k.sub.11], [k.sub.22] and [k.sub.33], associated, respectively, with splay, twist and bend deformation of the nematic structure.
The LC cell was filled with the nematic LC mixture E7 (Merck) in isotropic phase and then slowly cooled down to room temperature.
The flat plate of X-ray diffraction patterns for all copolymers shows only one broad diffuse halo at angles corresponding to 4.6-4.8 [Angstrom], which is characteristic [TABULAR DATA FOR TABLE 1 OMITTED] for a nematic structure.
viscosity increasing downstream because of the reduction of the initial orientation in the nematic melt; 2.
Disclinations are topologically stable line defects, characteristic of the nematic phase, around which the molecular orientation rotates by an integer multiple of [Pi] radians (10).
The Landau-de Gennes and Oseen-Frank models are the two most widely used continuum models to characterize equilibrium orientational properties of materials in the nematic liquid crystal phase.