New Thermochromic Liquid Crystals

Abstract

Liquid crystals are organic compounds which possess ordered fluid phases combining solid-like optical properties with liquid-like flow. The materials exploited for thermometric and thermographic use display a cholesteric (or chiral nematic) phase which has a helical disposition of molecules imposed by an asymmetry in their structure. The less mobile smectic phase, by contrast, is ordered into layers which cannot accommodate such a twisted structure. This smectic phase may appear in the same material as a cholesteric phase, on cooling to a lower temperature. A third liquid crystal phase, the nematic, contains symmetric molecules, has no intrinsic twist in its structure and is used in electro-optic devices.