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At one time it was firmly believed that there were three, and only three, states of matter: solid, liquid, and gas. This was the case in 1888, when an Austrian chemist named Friedrich Reinitzer, working at the University of Prague, was working on a cholesterol-based substance that didn’t seem to fit his expectations. As he tried to determine the melting point, he found that the substance, which was a solid crystal at room temperature, had two distinct melting points at 293.9ºF (145.5º C) and 353.3ºF (178.5ºC). In between those two points, it was a cloudy liquid, and when heated above the second point, it became transparent. Reinitzer consulted Otto Lehmann, an expert in crystal optics, who realized that the cloudy liquid was an unspecified state of matter, for which he coined the name liquid crystal.
A liquid crystal is a substance that is considered to be in between its solid and liquid phases. Often, its molecules are shaped like plates or rods — shapes that tend to align in a certain direction. The molecular order in liquid crystal can be altered by exposing it to electric, magnetic, or mechanical forces.
There are two main phases for a liquid crystal. In the nematic phase, which is close to being liquid, molecules float, but stay ordered. In this phase when a liquid crystal is what is called cholesteric, the crystals can create a twisted structure and reflect visible light in a temperature-dependent color pattern. The link between temperature and color allows them to be used in thermometers.
The other phase is the smectic phase. In this phase, the crystal is close to solid, and is ordered in layers. The liquid crystals move within layers, but not between layers.
The liquid crystal display (LCD) was developed in Princeton, New Jersey, at the David Sarnoff Research Center in 1963. Monochrome LCD digital watches were first manufactured in the 1970s, and the first commercial LCD television was built in 1988. LCD color computer monitors began to be sold in the 1990s, and outsold CRT monitors for the first time in 2003. As prices for LCD technology fell, more LCD televisions than either plasma televisions or CRT televisions were sold in the 2007 Christmas season.
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