What is Liquid Crystal?
The term liquid crystal is one of the names given to a state of matter intermediate between that of the conventional crystalline solid and isotropic liquid. Other names include mesophase and mesomorphic state. Liquid crystals possess the mechanical properties of liquids (they flow) and the optical properties of solids (they are anisotropic). They also possess some unique properties of their own which form the basis for their practical applications.
Many different types of liquid crystals exist. ATI's business is based on a particular class of liquid crystals known historically as cholesteric liquid crystals. These materials have the ability to selectively reflect light and the color of the reflected light can be made to change as the temperature changes. The normal color change sequence is from red to green to blue (through the visible spectrum) with increasing temperature within their color reflective temperature range. Because of their unique temperature-sensitive properties, the materials are also called thermochromic liquid crystals (TLC's). The rate of change from one reflected color to another as well as the specific temperatures at which certain color changes occur can also be accurately controlled.
The standard method of producing such devices, which is used by ATI, is to produce a coating (ink) containing preferably a microencapsulated Thermochomic Liquid Crystal (TLC) mixture and use a printing method to apply it to the supporting substrate. A black ink is then applied on top of the dry TLC coating and color change effects are viewed from the reverse (uncoated) side of the sheet. Liquid crystal thermometers/temperature indicators are usually comprised of a series of liquid crystal 'events', which change color in a sequence as the temperature changes. Behind or adjacent to each number (temperature) on the TLC thermometers is an 'active' area coated with a precisely calibrated TLC mixture designed to change color at the temperature in question.