Cholesteric Liquid Crystals and their Applications

The cholesteric phase in hquid crystals is analogous to the nematic phase but it is formed by materials that contain a chiral centre, initially derivatives of cholesterol (5.3), hence the name cholesteric LCs. Since synthetic chiral molecules can also be used on their own or as dopants for nematic LCs, e.g. (5.4), chiral nematic is probably a more appropriate term for these materials. 

Cholesteric LC materials are able to reflect visible light and also respond to temperature changes causing variations in the shade of the reflected colour. The 

The thermochromic behaviour of cholesteric LCs results from the fact that the pitch length, and hence the wavelength of the reflected light, is dependent on the temperature. 

Cholesteric LCs can act as hosts for dyes to produce coloured displays (see section 5.2.2.1 below) their temperature dependent colour change has found applications in thermochromic inks, ° and as pigments and copy safe colours their selective reflecting capabilities have been applied in colours and filters for reflective displays and projection systems, reflective polarisers and their electrical field induced switching in displays and smart reflectors, in colour patterning for full-colour recording.  

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