Liquid crystal
The crystals liquids are a class of materials that she can present in states of the matter understood between the Liquid and the Solid. In the crystalline liquid state (or mesomórfico, of the Greek Mesos Morphe: among two states) the materials present characteristic physical properties of the liquids simultaneously (former.: fluidity) and typical physical properties of the solids (former.: birrefringência).
These materials are constituted in general by molecules organic anisométricas. These molecules have one of their much larger dimensions than the remaining ones (former.: they can have a prolonged (small sticks) form or the form of disks).
In the state isótropo as in a liquid the molecules of the liquid crystal are disordered and their mass centers distributed aleatoriamente in the space, In the liquid-crystalline state the molecules can present varied levels of molecular order (former.: order orientacional and order posicional).
Typically a liquid crystal of prolonged molecules can join parallel amongst themselves second a direcção that she can define for a pseudo-vector that is designated by Nemático (something similar to toothpicks of matches inside of a box).
Depending on the temperature different values of order orientacional can be observed. In many liquid crystals the molecules possess dipolos eléctricos moment dipolar and they can be aligned through an electric field.
Some types of liquid crystals present strong colors that lose temper under the temperature action, pressure, electric and magnetic field, others have fast answer eletroóptica in the presence of electric field, for those reasons the liquid crystal was adopted in wide climbs for the electronic industry and it is used mainly in the production of of screens for televisions and monitors, besides the liquid crystal became the standard material for the displays production for electronic equipments of all of the types.
History
The first description of a liquid crystal was made by the Austrian chemist Friedrich Reinitzer in 1888. As his/her description, a certain molecule (the benzoic éster-acid of the cholesterol) presented a very colored appearance during his/her coalition and solidification.
He also noticed that that been composed turns liquid to the 145 °C, although some atypical characteristics in liquids, as appearance leitosa and it darkens, if they maintain until the 179 °C.
Above that temperature, the liquid stops a clear and “normal” appearance. Soon afterwards, the German physicist Otto Lehmann investigated that and other substances and it coined the term “liquid crystal.”
In the twenties of last century, fundamental researches were accomplished by the cienstistas Georges Friedel and Daniel Vorländer. However, the technical interest for liquid crystals only happened during the discovery of his/her capacity of change of states through properties eletro-optics, accomplished by George H. Heilmeier.
Concepts and introduction
The phases of liquid crystal, also known as mesofases, they constitute with disordered crystals and plastic crystals in a state joined own, denominated state mesomórfico. A composition that shows a phase of liquid crystal is called of mesógeno. In case that mesofase is a phase nemática, the composition is called of nematógeno. In case it is a phase esméctica, it is an esmectógeno.
A liquid crystal can be divided among liotrópico, termotrópico or barotrópico. In crystals liquid termotrópicos and barotrópicos the formation of his/her mesofase is dependent of temperature and pressure, respectively, in a pure substance. Already the formation in a mesofase liotrópica requests the presence of a solvent and it is dependent also of his/her concentration. Crystals liquid amfitrópicos present mesofases so much liotrópicas when termotrópicas. Mesofases stable (that is, independent of temperature and pressure) termodinamicamente healthy denominated enantiotrópicas. Mesofases metaestáveis are mesofases monotrópicas.
The application for the development of a phase of liquid crystal is the asymmetry of their constituent molecules. The great majority of the researched (besides the ones that constitute display cases of liquid crystal, like TVs of LCD) liquid crystals has molecules in stick (calamítico call) form. However, other possible formats exist, as discóide (he/she forms of disk), piramidóide (cone form), etc.
About the Author
Carla Sofia adores technology especially the technology LCD.Televisores LCD and see the Televisor Samsung LCD TV de 32 polegadas
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