Liquid crystal is a polymer material. Because of its special physical, chemical and optical characteristics, it has been widely used in thin and light display technology since the mid-20th century.
The familiar states of matter (also known as phases) are gas, liquid and solid, while the unfamiliar ones are plasma and liquid crystal (LC). Liquid crystal phase can only be produced by molecular combination with special shape. They can flow and have crystalline optical properties. The definition of liquid crystal has now been relaxed to include substances that can be liquid crystal phase in a certain temperature range and can crystallize normally at a lower temperature. The components of liquid crystal are organic compounds, that is, compounds centered on carbon. At the same time, liquid crystals with two substances are combined by intermolecular forces. Their special optical properties and sensitivity to electromagnetic fields have great practical value.
1888, an Austrian scientist named Leinitzel synthesized a strange organic compound with two melting points. When its solid crystal is heated to 145℃, it melts into a liquid, which is only turbid, while all pure substances are transparent when melted. If heated to 175℃, it seems to melt again and become a clear and transparent liquid. Later, German physicist Li Man called this turbid liquid "intermediate zone" crystal. It looks like a mule that is neither like a horse nor a donkey, so some people call it an organic mule. Since the discovery of liquid crystal, people didn't know its use until 1968.
The most common use of liquid crystal display materials is the display board of electronic watches and calculators. Why do they show numbers? It turns out that this kind of liquid crystal photoelectric display material uses the electro-optical effect of liquid crystal [1] to convert electrical signals into visual signals such as characters and images. Under normal circumstances, the molecular arrangement of liquid crystals is very orderly and appears clear and transparent. Once the DC electric field is applied, the molecular arrangement is disrupted, and some liquid crystals become opaque and dark in color, so that numbers and images can be displayed.
The electro-optic effect of liquid crystal refers to the optical phenomena such as interference, scattering, diffraction, optical rotation and absorption modulated by electric field.
Some organic compounds and polymers, in a solution with a certain temperature or concentration, have both liquid fluidity and crystal anisotropy, which is called liquid crystal. Liquid crystals whose photoelectric effect is controlled by temperature conditions are called thermotropic liquid crystals; Lyotropic liquid crystals are controlled by concentration conditions. Liquid crystals used for display are usually low molecular thermotropic liquid crystals.
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. This can indicate the temperature in the experiment. Liquid crystal will change color when it meets toxic gas such as hydrogen chloride and hydrocyanic acid. In chemical plants, people hang liquid crystal tablets on the walls. Once a trace of toxic gas escapes and the liquid crystal changes color, it reminds people to check and fill the loopholes quickly.
There are many kinds of liquid crystals, which are usually classified according to the characteristics of the central bridge bond and ring of liquid crystals. 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. Computer terminals and televisions made of liquid crystal materials can be greatly reduced in size. 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. 2. Why is it called LCD? Crystal liquid crystal-liquid crystal as early as 1850, Prussian doctor Rudolf? 6? Virchow and others found that the extract of nerve fibers contained an unusual substance. 1877, German physicist Otto? 6? Otto lehmann observed the phenomenon of liquid crystallization for the first time with a polarizing microscope, but he didn't know the reason of this phenomenon.
Frederick, a plant physiologist at the German University in Prague, Austria? 6? 4 Friedrich Reinitzer studied the role of cholesterol in plants by heating cholesterol benzoate, and observed the abnormal behavior of cholesterol benzoate during thermal melting on March 1883+04. It melts at 145.5℃, producing a glossy turbid substance. When the temperature rises to 178.5℃, the luster disappears and the liquid is transparent. The clarified liquid cooled slightly, became turbid again, and instantly became blue, and the color was blue-purple just before crystallization began.
After repeatedly confirming his findings, Lenin sought advice from the German physicist Lehman. At that time, Lehman built a microscope with heating function to discuss the cooling and crystallization process of liquid crystal, and later it was equipped with a polarizer, which was the most in-depth instrument for studying Lenezer compounds. Since then, Lehman's energy has been completely focused on such substances. At first, he called it soft crystal, and then renamed it crystalline liquid. Finally, he is convinced that polarized light is unique to crystals, and Fleeson de Cristal's name is correct. The name is only one step away from the liquid crystal (smooth ge crystal). Lenin Ze and Lehman were later called the fathers of liquid crystal.
Oxyazo ether synthesized by L. gattermann and A Ristschke was also identified as liquid crystal by Lehman. However, in the 20th century, the famous scientist G. tammann and others thought that Lehman's observation was only a phenomenon that tiny crystals were suspended in liquid to form colloid. W. Nernst thinks that liquid crystal is only a mixture of tautomers of compounds. However, the efforts of chemist D. Vorlander enabled him to predict which compounds are most likely to show liquid crystal characteristics through aggregation experience, and then synthesize these compounds, so the theory was proved.
Physical characteristics of liquid crystal
When it is turned on after being electrified, the arrangement becomes orderly and light can easily pass through; When there is no electricity, the arrangement is chaotic, which hinders the passage of light. Let the liquid crystal block or let the light pass like a gate. Technically, a liquid crystal panel consists of two pieces of quite exquisite sodium-free glass materials, called substrates, with a layer of liquid crystal sandwiched between them. When the light beam passes through this layer of liquid crystal, the liquid crystal itself will stand in rows or distort irregularly, thus blocking or making the light beam pass smoothly. Most liquid crystals belong to organic compounds and consist of long rod-like molecules. In the natural state, the long axes of these rod-like molecules are roughly parallel. Pour the liquid crystal into a machined groove plane, and the liquid crystal molecules will be arranged along the groove, so if those grooves are very parallel, the molecules are also completely parallel. What else is made of liquid crystal? One of the results of liquid crystal molecular arrangement is selective light scattering. Because this arrangement will be affected by external forces, liquid crystal materials have great potential in manufacturing devices. Chiral nematic liquid crystals between two glass plates can form different textures after a certain procedure.
Steroid liquid crystal selectively reflects light due to its spiral structure. The simplest thermometer (common thermometer in fish tanks) is made by using circular polarization in white light and according to the principle of color change. In medical treatment, skin cancer and breast cancer can also be detected by applying steroid liquid crystal to suspicious parts and then comparing with normal skin color (because cancer cells metabolize faster than ordinary cells, the temperature will be higher than ordinary cells).
Electric field and magnetic field have great influence on liquid crystal, and the dielectric behavior of nematic liquid crystal phase is the basis of various photoelectric applications (displays made of liquid crystal materials with external electric field have developed rapidly since 1970' s). Because they have many advantages, such as small size, low power consumption, low working voltage and easy design of multi-color panels. However, because it is not a light-emitting display, the clarity, viewing angle and environmental temperature limit in the dark are not ideal. In any case, TV and computer screens are made of liquid crystal, which is very beneficial. The previous large screen was limited by the demand of high voltage, and the volume and weight of the transformer were indescribable. In fact, color projection electric system can also use chiral nematic liquid crystal to make polarizer, filter and photoelectric regulator. 4. How to use the LCD screen in the computer and who invented it? LCD(Liquid Crystal Display (LCD) is an ultra-thin flat panel display device, which is composed of a certain number of color or black and white pixels and placed in front of a light source or a reflector. Liquid crystal displays are favored by engineers because of their low power consumption, and are suitable for electronic devices that use batteries.
Each pixel consists of the following parts: a row of liquid crystal molecules suspended between two transparent electrodes (indium tin oxide), and two polarization filters with perpendicular polarization directions. If there is no liquid crystal between the electrodes, the light passing through one filter will be blocked by the other filter, and the polarization direction of the light passing through one filter will be rotated by the liquid crystal, so that it can pass through the other filter.
Liquid crystal molecules themselves are charged. If a small amount of charge is added to the transparent electrode of each pixel or sub-pixel, the liquid crystal molecules will be rotated by electrostatic force, and the passing light will also rotate and change a certain angle, so that it can pass through the polarizing filter.
Before the charge is applied to the transparent electrode, the liquid crystal molecules are in an unconstrained state, and the charge on the molecules makes these molecules form a spiral or ring (crystal shape). In some liquid crystal displays, the chemical surface of the electrode can be used as a seed, so the molecules crystallize at a desired angle. The light passing through one filter rotates after passing through the liquid chip, so that the light can pass through another polarizer, and a small part of the light can be absorbed by the polarizer, but other devices are transparent.
After the charge is applied to the transparent electrode, the liquid crystal molecules will be arranged along the direction of the electric field, thus limiting the rotation of the polarization direction of the transmitted light. If the liquid crystal molecules are completely dispersed, the polarization direction of the transmitted light will be completely perpendicular to the second polarizer, so it will be completely blocked by the light. At this time, the pixel will not emit light. By controlling the rotation direction of the liquid crystal in each pixel, we can control the light that illuminates the pixel more or less.
Many liquid crystals will turn black under the action of alternating current, destroying the spiral effect of liquid crystals, and when the current is turned off, the liquid crystals will become bright or transparent.
In order to save electricity, LCD adopts multiplexing mode. In the multiplexing mode, the electrodes at one end are connected in groups, each group of electrodes is connected to a power supply, and the electrodes at the other end are also connected in groups, and each group is connected to the other end of the power supply. The grouping design ensures that each pixel is controlled by an independent power supply, and the electronic equipment or the software driving the electronic equipment controls the display of pixels by controlling the on-off sequence of the power supply.
The indicators for testing LCD display include the following important aspects: display size, response time (synchronization rate), array type (active and passive), viewing angle, supported colors, brightness and contrast, resolution and screen aspect ratio, and input interfaces (such as visual interface and video display array).
Inventor: The first operable LCD was based on Dynamic Scattering Mode (DSM), and George? 6? The team led by 1 Hailmann developed this LCD. Hailmann founded Optel Company, which developed a series of liquid crystal displays based on this technology. 1970 12, the rotational nematic field effect of liquid crystal is registered as a patent by Santer and Hoffman-lerouke Central Laboratory in Herfrich, Switzerland. 1969, James? 6? 1 Ferguson discovered the rotating nematic field effect of liquid crystal in Ohio University, and registered the same patent in the United States in February of 197 1. 197 1 year, his company (ILIXCO) produced the first LCD based on this feature, which quickly replaced the DSM LCD with poor performance.
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