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Nematic liquid crystal is a translucent liquid that changes the polarity of light waves passing through it. The word “nematic” comes from the Greek word for thread, and describes the thread-like formations that can form in the liquid crystal. Nematic liquid crystal is frequently used in liquid-crystal displays (LCD) screens such as those on digital watches.
Liquid crystals are an intermediate melting stage between a solid state and a liquid state. In 1888, an Austrian scientist named Freidrich Reinitzer discovered the state as he conducted experiments on a substance called cholesterol benzoate. The substance, Reinitzer noticed, had two distinct melting points. In the first it became a cloudy liquid, and in the second it became transparent. Reinitzer’s observations included the concepts that the cloudy or crystalline state changed the polarity of light waves passing through it, a concept imperative to the development of LCD.
Reinitzer never developed practical applications of liquid crystal technology, and research on crystalline states was largely abandoned in the early 20th century. In 1969, a scientist named Hans Keller successfully created a substance that would crystallize nematically at room temperature. This discovery lead to the ability to commercialize the product, and nematic crystals became extremely useful in screen technology.
The three states of matter that most people learn about in science class are liquid, gas and solid. Liquid crystal is a fourth state, somewhere between liquids and solids, and allows some forms of matter to pass through it. Like liquid substances, liquid crystal molecules do not have any positional order, but like a solid substance, the molecules in liquid crystal can have organizational order, meaning that they tend to point toward one direction over time. The nematic liquid crystal is a high temperature phase of the crystallizing process, where molecules have long-range organizational order.
Light waves from natural or artificial light sources vibrate in many directions. If most of the vibrations tend in a specific direction, the light is said to be polarized. By running light waves through nematic liquid crystal, the polarization changes, typically by rotating 90 degrees. If an electrical field is added to the crystal solution, the direction and amount of polarization can be controlled by the voltage of electricity.
In creating an LCD screen, two polarized pieces of glass are used, one with a thin filter of nematic liquid crystal. The glass is then hooked to two electrodes that can provide electrical charges. By running controlled charges through the glass, the nematic liquid crystal will twist and untwist, allowing only the electrically requested areas of light to go through. Screens using twisted nematic liquid crystal are common features in modern technology, used in laptops and digital clocks and watches.