Procedure based on G. H. Brown and J. J. Wolken, Liquid
Crystals and Biological Systems, Academic Press, NY, 1979, pp. 165-167 and
W. Elser and R. D. Ennulat, Adv. Liq. Cryst.2, 73 (1976).
These cholesteric-nematic liquid crystals reversibly
change color as the temperature changes. One of the principal advantages of
liquid crystals is their ability to map out thermal regions of different temperature.
Cholesteric liquid crystals can degrade when exposed to moisture or air.
As long as the mixture is stored in a sealed container it can be prepared
months in advance, although the sample may need to be remelted to mix.