At present, more than 10000 kinds of liquid crystal materials have been synthesized, among which there are thousands of commonly used liquid crystal display materials, mainly biphenyl liquid crystal, phenylcyclohexane liquid crystal and ester liquid crystal. Liquid crystal display materials have obvious advantages: low driving voltage, low power consumption, high reliability, large display information, color display, no flicker, harmless to human body, automatic production process, low cost, and can be made into liquid crystal displays of various specifications and models, which is convenient to carry. Due to these advantages, the sizes of computer terminals and televisions made of liquid crystal materials can be greatly reduced. Liquid crystal display technology has a far-reaching impact on the structure of display imaging products, and promoted the development of microelectronics and photoelectric information technology. According to the color change of liquid crystal, people use it to indicate temperature, alarm poison gas and so on. For example, liquid crystal can change from red to green and blue with the change of temperature.