Thermochromic mixtures, chiral nematics

Certain chiral nematic liquid crystals (or mixtures) are found to exhibit thermo-chromism, that is, temperature dependent selective reflection here the pitch length of such materials or mixtures is often found to have an inverse relationship with temperature and can depend on the nature of the material s mesomorphism. Thermochrom-ism is found to be at its most spectacular in materials which display chiral nematic phases and underlying smectic phases this is exemplified for a material with an I-N -SmA sequence (on cooling) and is shown schematically in Fig. 2. 

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