Liquid Crystal Properties And Notebooks LCD Screens

Liquid crystals are interesting because they don’t exactly fall under the three main states of matter: solid, liquid or gas. Liquid crystals are actually in an intermediate phase between crystalline solid and isotropic liquid. Discovered in 1888 by Friedrich Reinitzer, an Austrian botanist, liquid crystals are widely used in electronic displays.

Displays, such as notebook screens, use the fluidity and anisotropy (property of being directly dependent) of the liquid crystals. The anisotropy causes the dielectric constant and refractive index to vary on the orientation of its molecules.

Nematic, Smectic and Isotropic properties

One of the more common liquid crystal phases in the nematic phase. The nematic phase of liquid crystals is what makes LCD screens possible. During this phase, the molecules are in no positional order, but do have a notable pattern. This may cause the molecules to flow and their center of mass may shift randomly and distributed as if to be a liquid. They do, however, point in the same general direction.

Isotropic

Nematic

Smectic

Liquid crystals are affected by electric currents and when a voltage is applied, liquid crystals react and may change shape. A twisted nematic (TN) in naturally twisted, but when a certain voltage is applied it becomes untwisted. Displays use this type of liquid crystals because they can control light passage.

When heat is applied, most crystalline solids experience a transition to a different phase - to an isotropic liquid state. The intermediate stage, or mesophase, occurs in most substances. The temperature range for this phase is between the solid and isotropic state.

When bulked together liquid crystals often form micro droplets, which have different director orientations. When the numatic liquid crystal is heated, it turns to a liquid phase - this transition temperature is called the clearing point.

When the clearing point is achieved, there is a reduction in light scattering because of the lack of micro droplets and the different directors for each molecule.

If the temperature reaches above the clearing point, optimal viewing is reduced on the display and the display function may fail. Cooling of the molecules results in a phase change from the nematic to the smectic state, which causes the molecules to form a layer, creating a less than attractive display.

Thermotropic Liquid Crystals

Liquid crystals are categorized into two different types. Thermotropic liquid crystals are used in liquid crystal displays (LCDs) and react to change in temperature. The thermotropic liquid crystals are either nematic or isotropic. As mentioned before, the arrangement of isotropic is basically random, while nematic have a consistent pattern.

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