Cholesteric liquid crystal

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The image shows a rotation of the director about 180° in a cholesteric phase. The corresponding distance is the half-pitch, p/2.

A cholesteric liquid crystal is a type of liquid crystal with a helical structure and which is therefore chiral. Cholesteric liquid crystals are also known as chiral nematic liquid crystals. They organise in layers with no positional ordering within layers, but a director axis which varies with layers. The variation of the director axis tends to be periodic in nature. The period of this variation (the distance over which a full rotation of 360° is completed) is known as the pitch, p. The pitch is varying with temperature and it can also be affected by the boundary conditions when the chiral nematic liquid crystal is sandwiched between two substrate planes.

Examples of compounds known to form cholesteric phases are hydroxypropyl cellulose and cholesteryl benzoate.

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