A cholesteric liquid-crystal display (ChLCD) is a display containing a

liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. T ...

with a

helical Helical may refer to: * Helix, the mathematical concept for the shape * Helical engine, a proposed spacecraft propulsion drive * Helical spring, a coilspring * Helical plc, a British property company, once a maker of steel bar stock * Helicoil A t ...

structure and which is therefore

chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from ...

. Cholesteric liquid crystals are also known as '' chiral nematic liquid crystals''. They organize in layers with no positional ordering within layers, but a director axis which varies with layers. The variation of the director axis tends to be periodic in nature. The period of this variation (the distance over which a full rotation of 360° is completed) is known as the pitch, p. This pitch determines the wavelength of light which is reflected (

Bragg Reflection In physics and chemistry , Bragg's law, Wulff–Bragg's condition or Laue–Bragg interference, a special case of Laue diffraction, gives the angles for coherent scattering of waves from a crystal lattice. It encompasses the superposition of wave ...

). The technology is characterized by stable states i.e. focal conic state (dark state) and planar state (bright state). Displays based on this technology are called “bistable” and don’t need any power to maintain the information (zero power). Because of the reflective nature of the ChLCD, these displays can be perfectly read under sunlight conditions. Examples of compounds known to form cholesteric phases are

hydroxypropyl cellulose Hydroxypropyl cellulose (HPC) is a derivative of cellulose with both water solubility and organic solubility. It is used as an excipient, and topical ophthalmic protectant and lubricant. Chemistry HPC is an ether of cellulose in which some of t ...

and

cholesteryl benzoate Cholesteryl benzoate, also called 5-cholesten-3-yl benzoate, is an organic chemical, an ester of cholesterol and benzoic acid. It is a liquid crystal material forming cholesteric liquid crystals with helical structure. It can be used with choleste ...

. Some companies, such as

Chiral Photonics Chiral Photonics, Inc. is a photonics company based in Pine Brook, New Jersey, founded in 1999. The company is developing a new class of optical devices based on twisting glass optical fibers. These in-fiber devices aim to displace discrete optical ...

, have begun to explore CLCs as the basis for

photonic Photonics is a branch of optics that involves the application of generation, detection, and manipulation of light in form of photons through emission, transmission, modulation, signal processing, switching, amplification, and sensing. Though ...

devices. A US company, Kent Displays, has developed "no power"

Liquid Crystal Displays A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...

using Polymer Stabilized Cholesteric Liquid Crystals: these are known as ChLCD screens. A drawback of ChLCD screens is their slow refresh rate, especially at low temperatures. In 2009, Kent demonstrated the use of a ChLCD to cover the entire surface of a

mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...

, allowing it to change colours, and keep that colour even when power is cut off. The Industrial Technology Research Institute has developed a flexible ePaper called i2R based on ChLCD technology
ITRI
The German compan
BMG MIS
(formerly AEG MIS) has developed “Geameleon”- ChLCDs full color and monochrome in various sizes and resolutions. These ChLCDs can be used in extremely wide temperature applications i.e. for outdoor application. Various update versions can be applied to achieve a reasonable update time even at very low temperatures. Because of its very low power consumption, this technology is highly preferred to be used in self-sustaining applications (solar power applications).

References

Liquid crystals {{crystallography-stub