What is the cholesteric phase?
[kə′les·tə·rik ‚fāz] (physical chemistry) A form of the nematic phase of a liquid crystal in which the molecules are spiral.
What is cholesteric pitch?
In a typical cholesteric, the average twist-angle ψ between neighboring molecules (Fig. 1) amounts to a fraction of a degree. The resulting cholesteric pitch P, defined as the length along the twist axis corresponding to a full turn of the nematic director, is in the few-hundred-Ångstroms-to-micrometer range.
Why are cholesteric liquid crystals Coloured?
A color will be reflected when the pitch, the distance between layers that have the same orientation, is approximately equal to the colors wavelength of light. This change in pitch causes the color changes we see when we apply pressure to or heat or cool cholesteric liquid crystals.
What is pitch in cholesteric liquid crystal?
Cholesteric liquid crystals are consisted of nematic layers, with a small rotation of the director as we pass from one to the other. This rotation produces a helical structure and the distance to perform one full rotation of the director is known as the pitch length.
What are the applications of liquid crystal?
Liquid crystals are everywhere. They are used in all kinds of display devices including computer monitors and laptop screens, TVs, clocks, visors, and navigation systems. Each pixel in a monitor is an assembly of liquid crystals controlled by its own electromagnetic field.
What is the difference between nematic smectic and cholesteric liquid crystals?
The key difference between nematic smectic and cholesteric liquid crystals is that nematic liquid crystals have no ordered structure of molecules, and smectic liquid crystals have a layered molecular structure, whereas cholesteric liquid crystals have molecules in a twisted and chiral arrangement.
Why liquid crystals are anisotropic?
The anisotropic behaviour of liquid crystals is caused by the elongated shape of the molecules. The physical properties of the molecules are different when measured parallel or perpendicular to their length, and residual alignment of the rods in the fluid leads to anisotropic bulk properties.
How does a liquid crystal create a display?
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly, instead using a backlight or reflector to produce images in color or monochrome.