What are liquid crystals? Some organic solids having long rod-like molecules which do not melt to give the liquid substances directly. They instead, pass through an internet state called the liquid crystal state, often referred to as the liquid crystal. Thus the liquid crystal state is intermediate between the liquid state and the solid state.
The liquid crystals have a structure between that of a liquid and that of a crystalline solid.
In a liquid the molecules have a random arrangement and they are able to move past each other. In a solid crystal the molecules have an ordered arrangement and are in fixed positions. In a liquid crystals, however, molecules are arranged parallel to each other and can flow like a liquid.
Thus the liquid crystals have the fluidity of a liquid and optical properties of solid crystals.
Types of Liquid Crystals
According to their molecular arrangement, the liquid crystals are classified into three types.
Nematic liquid crystals: They have molecules parallel to each other like soda straws but they are free slide or roll individually.
Semectic liquid crystals: The molecules in this type of crystal are also parallel but these are arranged in layers can slide past each other.
Chlosteric liquid crystals: As in nematic crystals, in this type of crystal the molecules are parallel but arranged in layers. The molecules in successive layers are slightly rotated with respect to the layers above and below so as to form a spiral structure.
Application of Liquid Crystals
On account of their remarkable optical and electrical properties, liquid crystals find several practical applications.
Number Displays
When a thin of nematic liquid crystal is placed between two electrodes and an electric field is applied, the polar molecules are pulled out of alignment. This causes the be opaque.
Transparency returns electrical signal is removed. This property is used in the number displays of digital watches, electronic calculators, and other instruments.
Monitoring Body Temperature
Like the solid crystals, liquid crystals can diffract light. Only one of the wavelength of white light is reflected by the crystal which appears colored. As the temperature changes, the distance between the layers of molecules also changes. Therefore the colour of the reflected light changes correspondingly. These cholesteric liquid crystal undergoes a series of a color changes with temputure. These crystals are used indicator tapes tapes to monitor body temperature or to spot areas of overheating in mechanical systems.
