What is Liquid Crystal Display?
Liquid Crystal Display
Liquid crystals are of two types: thermotropic liqid crystals prepared by heating the substance and lyotropic liquid crystal made by mising two or more compounds. Some of the imporatant liquid crystals that belong to the first category are p-azoxyanisole cholesteryl nonanoate and p-n octyloxybenzoic acid. In the second category sodium stearate and alpha-lecithin are the two imporatnat liquid crystals. Liquid crystals are used in used in colour TV and electronic display tubes sensitive tapes and electronic device for digital clocks watches and calculators. Liquid crystal displays work on two principles viz dynamic scattering and field effects.
In displays the liquid crystals are sandwiched between two transparent electrodes. The thickness of a liquid crystal film varies from 6 to 25 microns. The cell is sealed to eliminate oxygen and moisture. In dynamic scattering if no electric field is applied the cell is transparent. On applying electric field to the crystal the cell becomes opaque. Digital displays are made by photoetching a seven-segment pattern on tin or indium-coated glass plate. The field effect displays are mostly used in watches and calculators. The output of quartz crystal is given to seven segments of liquid crystalin a watch. Polarizers are also used for liquid crystal cells. Electric field changes the molecular alignment by which liquid crystal becomes opaque on account of a mirror behind the second polarizer.
