Liquid crystal is a substance that can flow like a liquid, yet has properties that are characteristic of a solid crystal. The most common use of liquid crystals is in liquid crystal displays (LCD’s). Those displays range from small units for watches, calculators, cellular telephones, and handheld computers called personal digital assistants (PDA’s) to large displays for automobile dashboards, computer screens, and television sets.
The most useful property shared by solid and liquid crystals is the arrangement of the tiny particles of which they are composed. In a solid crystal, the particles are atoms, and the atoms are aligned with one another. In a liquid crystal, the particles are molecules, and normally the molecules are lined up—though not as uniformly as in a solid crystal.
A unique property of liquid crystals enables scientists and engineers to make use of their molecular alignment: The alignment can be disrupted electrically, magnetically, or by a temperature change. A crystal that is normally clear becomes murky. A colored crystal changes color.
An LCD uses voltage to disrupt the alignment. The display consists of many small pixels (picture elements). Each pixel is made up of many liquid crystals that are normally clear. Applying a small voltage to a pixel disrupts the alignment of its liquid crystal molecules. The pixel may become black or various shades of gray.
In a color LCD, light from the liquid crystal passes through filters that produce the colors. Liquid crystal thermometers use crystals that change color as their temperature varies.
See also Thermometer (Liquid crystal thermometers) ; Watch (Quartz watches) .
