Importance

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Abstract

The present invention relates to liquid crystal temperature indicating compositions, preferably absent cholesteric liquid crystal material, and the containing of such compositions in volumes formed in a containment medium that tends to distort the liquid crystal structure when the temperature thereof is below a transition or clearing point temperature. The containment medium is water resistant, e.g. insoluble in water, and preferably has heat and optical stability, e.g. does not brown or otherwise discolor, at relatively high temperatures, e.g. above 100.degree. C. Plural liquid crystal materials having different transition temperatures may be mixed to form a liquid crystal material having a transition temperature intermediate those of the ingredients. In such distorted or curvilinearly aligned mesomorphic phase, the index of refraction of the liquid crystal is different, preferably greater, than that of the containment medium; therefore, incident light will be scattered, preferably isotropically, and such scattered light can be used as a temperature identifier. However, above a transition temperature, the liquid crystal material changes to an isotropic phase, which is substantially optically transparent, on the one hand; and the liquid crystal is so selected such that in the isotropic phase it has an index of refraction substantially matching that of the containment medium. Incident light is transmitted by the isotropic liquid crystal and, accordingly, provides another temperature identifier. The scattering liquid crystal material will appear visually brighter than the transmitting liquid crystal material.

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First Claim