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.
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. See LCD
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
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.