liquid crystals

The term liquid crystal is a paradox; Because the word crystal refers to a specific spatial network, but the formation of a crystal network in liquids is not possible. In these materials, specific molecular orientation occurs under certain conditions, so it is better to call them spherical heterogeneous liquids.

Matter has four states; solid, liquid, gas, and plasma.

In solids, molecules keep their alignment and maintain their position relative to the surrounding molecules, the behavior of molecules in liquids is the opposite; They can change direction and move anywhere.

Some substances are in an intermediate state, partly liquid and partly solid. Their molecules tend to keep their alignment (like solids) but also move (like liquids). Therefore, a liquid crystal is neither a solid nor a liquid, but it is closer to a liquid than a solid.

In a crystal, the molecules are arranged in a precise geometrical lattice, and although they vibrate in place, the electrical forces prevent them from disturbing their geometrical structure, unlike in liquids. Liquid molecules are free to move around and slide over each other, which is why they take the shape of their container. In liquid crystal, molecules show both behaviors and for this reason these substances usually have high viscosity (like honey). The molecules of these substances can be considered rods due to their extreme polarity. Under conventional conditions, electric attraction tends to arrange molecules in special patterns (a bit like hydrogen bonding in water).

It takes a considerable amount of heat to transform a suitable material from a solid to a liquid crystal, and a little more heat to transform that same liquid crystal into a true liquid. This explains why liquid crystals are so sensitive to heat and are used to make thermometers. This also explains why laptop screens behave strangely in cold weather and very hot days; Therefore, it is better to call them round inhomogeneous liquids.

Liquid crystals are neither completely liquid nor completely solid, physically they look like liquid flow, but they also have some properties of crystalline solids. Liquid crystals can be considered crystals that have lost some or all of their positional order, while retaining orientational order.

Between 1850 and 1888, researchers in the fields of physics, chemistry, biology, and medicine discovered that some substances exhibit strange behavior at temperatures close to their melting point. They observed that the optical properties of these materials change discontinuously with increasing temperature.

These materials (liquid crystals) consist of organic molecules that have an elongated shape with a fixed central region and flexible edges.

The anisotropic behavior of the liquid crystal is caused by the length of its molecules. The physical properties of molecules along parallel to the physical properties along perpendicular to the plane of the molecule are different. This difference in the properties of the molecules causes the difference in the bulk properties of that substance (large volume of the substance).

Imagine a large number of toothpicks placed irregularly in a rectangular box. When you open the toothpick box, the toothpicks are almost in the same direction, but not in the same direction, that is, the angle between each toothpick with a certain axis is different. (They are not exactly along a line, but their direction is, for example, inclined to the north). They move freely but the direction of their movement is the same. This type of liquid crystal is known as nematic.