As its optical properties of certain liquid crystalline substances in the presence or absence of an electric field, liquid crystal material can find wide use in liquid crystal displays. While in most technological applications, the liquid crystal monomer is unable to meet technical requirements, a mixture of two or more liquid crystals can be used to improve the properties. For example, eutectic mixtures of different liquid crystals are used, in order to tune the temperature range where the N phase is stable[1] and reduce response time through optimization of viscoelastic properties. The structure and physical properties of liquid crystal mixtures are a function of composition, and small changes can have pronounced effects on observables.
When the light enters to a liquid crystal phase, it will be reflected if the pitch of the liquid crystal matches with the wavelength of the light. For liquid crystal with a small pitch, small wavelengths of light will be reflected (i.e. blue light, see Figure 1). For liquid crystal with a large pitch, long wavelengths of light will be reflected (i.e. red light). The pitch of the liquid crystal can be changed by changing the temperature of the liquid crystals phase. As a result, the color of light reflected by the liquid crystal is changed. The pitch of a liquid crystal is a molecular level property. Thus, any large-scale property changes (like color) you see in the liquid crystal displays are a result of tiny, molecular level properties changing.
Fig. 1 The visible light spectrum with wavelengths
In LCD (liquid crystal display) technology, only nematic liquid crystal has practically use and cholesteric liquid crystal is doped with small amount to help nematic liquid crystal molecules to twist. Four types of nematic liquid crystal mixtures commonly used in LCD fields are TN (twisted nematic), HTN (homeotropic twisted nematic), STN (super twisted nematic) and TFT (thin film transistor) .
TN liquid crystals are the most common type of LC's used in the display industry. TN cells are basically 90° liquid crystal polarization rotators. This twisted nematics configuration can produce images in two modes: Positive or Negative. Positive Mode provides white background and white segments. TN liquid crystals are mainly used in electronic watches, calculators, simple handheld game consoles and other simple consumer electronics in black and white monochrome.
HTN (homeotropic twisted nematic) liquid crystal is a type of liquid crystal with a higher molecular twist (usually 110°) than TN (90°). Hence it can offer wider viewing angles and improved contrast. This type of LCD is characterized by high contrast, low power consumption, low driving voltage, and poor dynamic driving performance.
STN (super twisted nematic) liquid crystal has a twist angle of about 180–270° (with 240° being fairly common) with a consequent increase in the complexity of images that can be displayed. Generally, the STN technology comes in two colorations, Green STN and Silver STN. The STN-Green has dark violet / black characters on a green background. The STN-silver has dark blue / black characters on a silver background.
TFT LCD Display (thin-film-transistor liquid crystal display) technology has a sandwich-like structure with liquid crystal material filled between two glass plates. Two polarizer filters, color filters (RGB, red/green/blue) and two alignment layers determine exactly the amount of light is allowed to pass and which colors are created. This type of display can be used in television sets, computer monitors, mobile phones, handheld devices and others.
Alfa Chemistry offers various liquid crystal mixtures. If you do not find the products you need, please feel free to contact us. We also offer product customization according to customer's detailed requirements.
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