1. Basic knowledge and physical properties of liquid crystals
1.1 basic knowledge of Liquid Crystal
In nature, most materials change with temperature only in three states: solid state, liquid state and gaseous state.
Liquid crystal (liquid crystal) is a new material state which is different from the usual solid, liquid and gaseous state,It is the material state of liquid and crystal in a certain temperature range. It is also called liquid crystal phase or intermediate phase, so it is also called the fourth state of matter. The liquid crystal was first discovered by Leni F M, a botanist in Austria in 1888 (F.Reinitzer).
The liquid crystal is an organic compound with the regularity of molecular arrangement between a solid and liquid crystal, generally the most commonly used for nematic liquid crystal (nematic), molecular shape is slender rod shape, length and width is about 1~~1 0nm, in different current electric field, the liquid crystal molecules will do regular rotation of 90 DEG arrangement. Have the transmittance difference, so the power supply is switched on and switched off (ON / OFF) when the difference between light and shade, and control principle of each pixel, can constitute a desired image. There are many kinds of liquid crystals, and there are thousands of kinds of liquid crystals in nature or synthetic. However, from the composition and the physical conditions of the liquid crystal phase, the liquid crystals can be classified into two categories: thermotropic liquid crystals and lyotropic liquid crystals.
Some organic compounds are heated and dissolved, and the liquid crystals formed by the destruction of crystalline lattices by heating are called thermotropic liquid crystals, which are the liquid crystals due to the change of temperature. Some organic compounds are placed in certain solvents,
The liquid crystal formed by the destruction of the crystal lattice by solvent is called lyotropic liquid crystal. It is the liquid crystal phase due to the change of the concentration of liquid crystal, such as soap bubbles in the air played by children, which is the most common example of lyotropic liquid crystals. Most of the liquid crystalline materials currently used for display are thermotropic liquid crystals.
1.2 Physical properties of Liquid Crystals
Liquid crystals are partially ordered materials composed of rod molecules, disk molecules, and other molecules without spherical symmetry.
It differs from dry molecules in arranging completely disordered isotropic liquids, and also arranged perfectly ordered crystals of non dry molecules.
The molecular arrangement between the crystal and the liquid and the special shape and properties of the molecule lead to the liquid crystal and even more complex properties of the liquid crystal. On the one hand, liquid crystals have fluid flow characteristics; on the other hand, liquid crystals exhibit spatial anisotropy, including dielectric properties, magnetic polarization, optical refractive index and other spatial anisotropy.
The partially ordered arrangement of the liquid crystal molecules also makes the liquid crystal similar to the crystal and can withstand the shear stress that disturbs this order. That is to say, liquid crystals have shear modulus of elasticity.
In practical applications, the mobility of liquid crystals, the anisotropy of dielectric and optical properties, and the elasticity of liquid crystals are important. They can control the parameters of liquid crystal display. The liquid crystal material has many technical parameters, including optical parameters, and physical parameters, the main dielectric anisotropy of delta 6, birefringence n, bulk viscosity doors, elastic constants of K, T m T C phase transition temperature, resistivity and liquid crystal P.