Whenever we study the properties of crystalline solids, we come to know that the pure solids melt sharply. The temperature remains constant at the melting point until all the solid melts.
In 1888, Frederick Reinitzer, an Austrian botanist discovered a universal property. He was studying an organic compound cholesteryl benzoate. This compound turns milky liquid at 145 degree Celsius and becomes a clear liquid at 179 degree Celsius. When the vape juice substance is cooled, the reverse process occurs. This turbid liquid phase was called liquid crystal.
Up til now, it has been reported that there are many crystalline solids which melt to a turbid liquid phase before finally melting to a clear liquid. These turbid liquid phases can flow as liquids. They have the properties like liquids as surface tension, viscosity, etc. But it is very interesting to know that the molecules of such turbid liquids posses some degree of order as well. It means that these turbid liquids resembles crystals in some properties and the most important properties are optical once. These turbid liquids are hence called liquid crystals. So, a liquid crystalline state exist between two temperatures that is the melting temperature and clearing temperature. A crystalline solid may be isotropic or anisotropic, but liquid crystals are always isotropic.
From 1888 to until about thirty years ago, they were largely are laboratory curiosity. But now they have found a large number of applications.
Those substances which make the them are often compose of long rod like molecules. In normal liquid phase these molecules are oriented in random directions. In liquid crystalline phase, they develop some ordering of molecules. Depending upon the nature of ordering, it can be divided into:
The properties of liquid crystals are intermediate between those of crystals and isotropic liquids. They have the fluidity of the liquids and the optical properties of the crystals.
Uses Of Liquid Crystals:
Due to the remarkable optical and electrical properties, they have many practical applications. Many organic compounds and biological tissues behave as fluid crystals. The unique properties of crystals have intrigued the scientists since their discovery, nearly hundred years ago.
Some of their important uses are as follows:
- Diffraction Of Light:
Like solid crystals, they can diffract light. When one of the wavelength of white light is reflected, from a liquid crystal it appears colored. As the temperature, changes the distances between the layers of molecules of liquid crystals change. Therefore, the color of reflected light changes accordingly. Thus they can be used as temperature sensors.
- Detection Of Potential Failure:
They are used to find the point of potential failure in electrical circuits. Room thermometers also contain them with the suitable temperature range. As the temperature changes, figures show up in different colors.