Liquid crystal is a phase state, in which a substance has both liquid, and solid properties at the same time. In other words, a substance possesses fluidity and anisotropic properties. Liquid crystals have a structure of viscous fluids, which is composed of the molecules of a disk-like shape. Orientation of these molecules can change due to the interaction with electric fields.
Liquid crystals (LC) are usually divided into two groups:
- Thermotropic liquid crystals, which are formed due to heating of a solid substance. These LCs are able to exist under specific temperature and pressure. They in turn are divided into three types depending on the molecules’ arrangement:
- Smectic LCs: they have a layer-like structure, with the layers being able to displace with respect to each other. The layer density can change, when approaching to a surface. These LCs have relatively large viscosity.
- Nematic LCs: they do not have a layer-like structure. Their elongated molecules slide continuously along their long axes, while rotating around them. These LCs are similar to liquids.
- Holistic LCs: they form in the combinations of different steroids, for example, cholesterol. They have a lot in common with nematic LCs, except for the position of molecules. Long axes of the molecules of the holistic LCs are rotated with respect to each other so that the molecules have a spiral shape. The molecules of the LCs of this type are extremely sensitive to any changes in temperature and change its orientation and therefore the spiral itself with respect to temperature. Depending on the spiral, the holistic LCs change its color. Because of the latter property, these LCs found a wide application in different fields of human activity.
- Liotropic liquid crystals, which form in the mixtures of rod-shaped molecules of the given substance and polar solvents (for example, water)
Application of LCs is very wide. LCD monitors, thermography, and electronic indicators are among the most common uses of LCs.