What is the "Liquid Crystal" inside an LCD Screen?

2026-06-04 15:18:35

The "liquid crystal" inside an LCD screen, as one of the three main materials of an LCD, plays a significant role.

1. Basic Concept of Liquid Crystal Displays

Liquid crystal is a new physical state. It was discovered in 1888 by Austrian scientist Friedrich Reinitzer. When a substance is heated to the melting point of its crystal, it becomes a milky, turbid liquid. With continued heating, this milky liquid turns into a completely transparent liquid. This phenomenon also occurs correspondingly during the cooling process. Observation under a polarizing microscope reveals that this milky liquid is different from ordinary liquids, exhibiting optical anisotropy — meaning the molecules within the substance are arranged in an orderly manner. This differs from traditional concepts of solids and liquids, hence it is defined as liquid crystal.

2. Main Uses of Liquid Crystal Characteristics

1. Relative Temperature (T) : It must be ensured that the entire system remains in the nematic phase within the required temperature range, without crystallization or other phases (such as smectic phase).

2. Dielectric Anisotropy (Δε) : Adjust Δε to meet user requirements for threshold voltage.

3. Optical Anisotropy (Δn) : Adjust Δn to meet user requirements for different cell gaps.

4. Pitch (P) : An important parameter used to determine the cell gap and the amount of chiral dopant added.

3. Precautions for Using Liquid Crystal

1. Effect of Ultraviolet (UV) Light
   UV light can break C-C bonds and polymer C chains, affecting the performance of the liquid crystal.

2. Effect of Temperature
   Liquid crystal is less sensitive to temperature than to UV light. During use, the heating time of the liquid crystal should be minimized, and heating to higher temperatures should be avoided. It is recommended not to exceed 35°C above the clearing point.

3. Environmental Effects
   The resistivity of liquid crystal is ${10}^{11}-{10}^{12}$ Ω/cm². Small amounts of conductive materials can lower the resistivity.

4. Container Effects
   It is best to use hard glass (high silicon boron glass). Ordinary glass bottles are made of soda-lime glass, and storing liquid crystal in such containers can reduce its resistivity.