Why say liquid crystal is neither nor liquid?
Solids are generally divided into two broad categories: crystalline and noncrystalline (amorphous), such as quartz, mica, ice, metal, etc., crystalline. The crystal has a regular geometric appearance. When it is heated to a certain temperature, the crystals will begin to liquefy at the melting point until eventually turning into a liquid. Crystals also have some special properties. For example, graphite, when heated, expands in some places but shrinks in others; When peeling off the thin mica sheet, we can often see it like this: in the direction parallel to the thin mica plate, it is easy to separate it, but in the perpendicular direction, a great force must be used to be able to tighten the thin lids. That property of a crystal is called anisotropy. Also, like glass, paraffin, rubber, etc., tense is noncrystalline. Noncrystalline has no clear shape, also has no melting point, much less anisotropy.
As early as 1881, it was discovered that, during the liquefaction process, some crystals do not have to turn into ordinary liquids, are isotropic, have only one melting point, but can appear as two melting points. At the two melting points, the crystal state is not the same. When the temperature reaches the first melting point, the crystal liquefies into a messy viscous liquid. As the temperature rises to the second melting point, the liquid becomes visibly clear. We call the first melting point of the crystal and the second melting point of the crystal. When the temperature is within the range of melting point and transparency, the crystal is called the liquid crystal state. Objects that enter a liquid crystal state have both the liquid’s flowability and the heterosexual directions of the crystal. But ordinary fluids are homosexual, so the liquid crystal is not a liquid. Absolutely crystal has a certain geometric shape, so it is impossible to consider liquid crystal as crystal.
There are many types of liquid crystals, in which a molecular structure of a liquid crystal displays a spiral, called a cholesteric liquid crystal. Under the sun’s irradiation, following the rising temperature, this liquid crystal will appear in different colors in order: red, orange, yellow, green, blue, indigo, purple as evil magic. When the temperature drops, it will revert in the reverse order. Some liquid crystals are highly sensitive and discoloration occurs rapidly when the outside temperature changes less than 1 ° C.
Taking advantage of this feature of the liquid crystal, liquid crystal detectors and indicators have been made to check the temperature. When you wear an electronic watch on your hand, the numbers that constantly blink and change in turn are the characteristic expression of the liquid crystal.