Liquid Crystals And Their Applications

Liquid Crystals And Their Applications

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  Liquid crystals andtheir Applications Submitted to: Dr. Shahzad A. S. Chattha Supervisor: Madam Aqdas Noreen Submitted by: Muhammad Minhas Azeem Roll No.7616 Dept. of Applied Chemistry&Biochemistry Government College University Faisalabad.
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  Contents 1. Liquid crystals 2.History 3. crystal and liquid crystal 4. Phases of liquid crystals 4.1 Nematic Phases 4.2. Smectic Phases 4.3. Cholesteric Phases 4.4. Columnar Phases 5. Construction of LCDs 6. Advantages of LCD 7. Applications 8. References
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  1. Liquid crystals Thereare different types of material in natuer.These types of mater is also called state of matter.The nature of matreial depends upon types of attrection present between the molecules and mobility of atom and molecules.Main state of matter is three types: (i) solid state (ii) liquid state (iii) gaseous state In solid stae , attraction between atoms and molecules is high. Molecles are close to each other inter moleclar forces between the atom or molecules is high.So molecules of solids have fix orientition in space which keep the molecule fix shape.So these properties soilds have high melting and boiling point.In liquid state of matter, attractive forces between the molecules is weak as compared to the soild but strong as compair to gass.The molecules of liquids have more empty spaces as compair to the soild , attractive is weak the molecules move aroud with each each other but molecules remain close to each other so fluid donot have fix shape and adapted the shape of container that hold it.While in the cause of gass attractive forces among the molecules is weak.The molecules are faraway from each other.The molecules have large empty spaces so the atoms or molecules of atoms are compressable.The gass molecules have high empaty spaces molecules of gases move randomly so the molecules of gass will expand and fill the container. Three states of matters have several intermediaete states , gel is a example of intermediat state.It is like a solid and like a liquid.the liquid crystal is also anoter example of intermediate state which have both solid and liquid phase . Liquid crystal have solid like propertis but flow like liquid.The liquid crysatals are first observe in cholesteryl benzoate.It is first liquid crystal. It is state between solid and liquid crystal. It have some specific properties of a liquidity, droplets properties as well as some crystalline properties. The liquid crystals is a material that show properties of liquid and some time soild it is substanc that like liquid and like a solid.It is slipary in nature like a soap.This liquid crystals are find in soap dish.
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  In a liquid,all type of molecules flow around anyway . Solid, the molecules have strong attrective forces among them.They are attrack with each so they have regular pattern and they are arrange in specific shape. 2. History In 1888, the Austrian chemist Friedrich Reinitzer was perform experiments to discover correct formula and molecular weight of cholesterol. He was working on melting point. It show veriation in melting point, He observed two melting points (178.5o C and 145.5o C). When the temperature of solution reach at 145.5 o C solution become milkey when the teperature increase upto 178.5 o C.The solution become transparent. He thought that changes between two teperature is due to some impuritis but when he purify the solution he foud that this changes remain still so he thought that obtaining of clear liquid is property of solution. Otto Lehmann a German physicist,. He found that change the clour was new state of matter.it is intermediate state.This new state was named "liquid crystal,"it was intermediate properties of solid and liquid state of matter, distribute important properties of both. In the 1960s, a French theoretical physicist, Pierre-Gilles de Gennes, He had worked on liquid crystal and got nobel prize in Physics 1991. 3. Crystals and liquid crystal The solid crystals and liquid crystals are different to each other due to properties.The liquid crystals are oriented with three dimension stucture in the space.These three dimension stucture indicate that crystals are optically active and rotate the plane polarize light.Liquid crystals show twisted stucture while solid crystals donot show twist stucture.In liquid crystals two different phases solid and liquid phase are mix with specific proportion but in soid crystalphases donot have. Liquid crystals are active molecules in liquid crystals molecules of crystala sre thin, long like a french fries. Even if the molecules' position share randomly, their possition can be orientation with a regular pattern-then they show regular and order stucture of liquid crystal.
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  Fig:Liquid crystals The liquidcrystal molecules do change the polarization of light. A polarizing filter works by absorbing a particular component of the electric field. The liquid crystal molecules don't absorb anything However, if they're arranged in the proper way, they can "twist" the light--that is, rotate the plane in which it is polarized. if polarized light goes through the molecules, it comes out polarized in a different direction. the light is sent through that first polarizer before it enters the liquid crystal. 4. Liquid Crystal Phases Ordinary liquid have same physical propeties such as electrical and megnetic properties. Genrally in the fluid molecules in the liquid have unequal axes. This unsymetric behavior effect rotation and orientation of light.
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  4.1Nematic One of themost familiar liquid phase phases is the nematic. The word nematic drived from the Greek word, ‘nema’’ which means "thread". In nematic phase molecules havesame direction in space but change the order. Fig: Nematic phase Medium size organisc molecules are use to make crystal which are enlarge as a cigar.When temperatures is incrase , the molecules will be align immediately, as shown in the figure,at high temperature molecules are arrenge this sequence , they are ordered oriented ,so they form nematic liquid crystals. The nematic phase is most important phase because they have lot off application for developing liquid crystals.In nematic crystal phase molecules are arranged paralell to one an other other. In this figure molecules are arrenge in rod shape linkage of crystal molecules. It have two or more ring fixed by a central linkage group. Typical shape of a liquid crystal molecule
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  4.2 Smectic Phases "Smectic"is a Greek word which means soap.This is just like a slipary soap which is present in the lower side of soap dish. In the smectic state,the molecules are arrenge in layers or planes they show general stuctural order in nematics. Some compound are develop many types of smectic phase . The most common phases have been recognize here.  smectic-A in smectic-A there is paralell position of director and smectic plane. The orientation of molecules is disturb in the plane.  smectic-B in mesophase orientation of molecules are just like a smectic A ,the molecules are arranged in layer which foem hexagonal stucture ..  Smectic-c mesophase molecules are oriented as same order A,B but in smectic-c smetic phase is measure by rotation of angle. Fig: sematic phase Director of sematic phase have chiral centar which rotate plane polarize light . chiral centar is indicate by C*.Mesophase have different orientation and direction in the space.these layers of mesophase is not parallel or perpendicular with each other.These one layers rotate from layer. To next layer.the diagram of each later is shown in fig. otation of layer is represent by green arrow.the rotation of layers form helix stucture..
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  4.3.Cholesteric Phases: It istype of liquid crystal .It has chiral centar and helical in stucture.This types of liquid is also known as chiral numatic liquid crystal. They arrange in sheet with no region arrenging within layers, but a director axis which changes with layers. The changes of the director axis regularly in nature. This regular changes is called pitch,it is repersent as p. The pitch changes with temperature and it is also be disturb by the boundary conditions when the chiral nematic liquid crystal is embaded between two substrate planes.. Examples of cholesteric phases are hydroxypropyl cellulose and cholesteryl benzoate. . Fig. Cholesteric Phases
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  4.4 Columnar Phases Arrengementof crystal in column phase is structually different from above phases.The liquid crystals are arrenge in disk shape stuctures which join to form the column so this arrengement is complex in nature. The columns are arrenge new mesophase. The new mesophase is two dimensional stucture 5.Construction of a liquid crystal display LCD consist of many small rod shape molecules .These rod shape molecules are liquid crystals.these molecules have liquid like characters.These liquid crystals have ability to curve and rotate the light in different direction.
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  Fig.Construction of LCD Thereare three function which make LCD.the first function is source of back light.secound function is polarization of light source and third function is liquid crystals which change the polarize light To genrate the clour in LCDs colour filter is use.clour filter have primary clour such as green ,red ,blue.these colour genrate million of clour scheme.these filter is plase in face of pixal.In TFT different capacitor and transistor is use which control the pixal of display.it has flat panel. 6.Advantages of LCDs  Brightness. Liquid crytstal Prepared very clear bright images due to high peak resolution.it shows very bright and clourfull picture.  Emissions .It produce considerably lower electric, magnetic and electromegnetic feilds than CRTs.  Geometric distortion. Geometric curvature at native resolutions.minor distortion can occur for other resolutions.  Power consumption:Lcd take take less electricty .it mostly take 12 volt.it consume less than 1/3 the power of comparable CRT.It produce less heat.  Physical aspects:LCD is thick sharp bright clour take up about 40% less desk space.  Screen shape:Completely flat screen  Shapness: due to native resolution highly sharp immage is produse.Color are resolution of image is sharp.no colour bands is produce. 7.Applications: 7.1. The liquid crystal thermomete A liquid crystal thermomete change the colour by changing the temperature. The liquid crystal s show change .These crystals change colors from black, red, yellow, green, and blue. The curent temperature is find.the liquid crystals change into green..if green clour is not appear then temp becom interndiate.
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  7.2 Optical imaging Thistechnique is ue for tratment of diseases,diagnosis and treatment of medical office .in these techinque rays are passed through demage area such as tumour and facture,camera is attach to the computre which show image on computer. ultraviolet, and infrared rays are use for detection of diseases and image appears on secrean. 7.3 Helmets and bullet proof vests Polymer liquid crystal is high,strong .fiexable,dense material.It is use in industry level.it is use to make the high strength fiber.Kevlar use this material to make helmets and bullet-proof vests.this material is light in weight but have high srength and resistance. Ordinary polymers have no capasity to compeat the material such as steel.It is observed that long chain polymerse have strong and high capasity then ordinary polmerce. 7.4 Battery testing strips(used by Dura Cell) It is important property of liquid crystals,it indicates the amount of charging store in the batter.When the electric current passing through medium it genrate heat.due to excess of heat orientation of layer take place which change the the layers orientation to produce a colour change.
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  7.5 Slugs andsnails(nature)  In nature liquid crystal is also present. Slugs and snails are produce liquid crystals in the soil .Soil particles acts as solid while mucus which secrat snails act as liquid phase it is important application of liquid crystal.they provide moisture and wetting to the soil.they secreat mucus which align the soil particles in specific pattren .  Liquid crystal present in biological cell membrane. 7.6 Future Application  Smart window  3D display  Synthesize biological membrane  Computer LCD  Use in cell phone  LCD’s watch The world lagest LCD is103 fit,Beijing.
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  8. References: 1: P.Gde Gennes, Port.j , 2010 “The Physics of Liquid Crystals”, ref 5. 2: M. J. Stephen, Excellent review of basic properties 3: J. P. Straley “Physics of liquid crystals”, Ref. [2]. 4: D. Fincham, rotational motion of linear molecules, 1984 , 47–48. 5: http://www.slideshare.net/Nawarajintermediate/liquid-crystal-and-its-application# 6: Stegemeyer H, Blumel T, Hiltrop K, Onusseit H and Porsch F, Liq. Cryst. 1986,1-28. 7: Tanimoto K and Crooker P,1985, Phys. Rev. A 32 1893-5. 8: Tsvetkov V, Acta Physicicochim (USSR) , 1942 (16- 132). 9: van der Meer B Wand Vertogen G, Phys. Lett, 1976. 59A( 279-81). 10: Wright D C and Mermin N D, Phys. Rev, 1985. A 31 3498-500. 11:Thoen J. 1988 Phys. Rev. A 37 1754-9 12 Tsvetkov V 1942 Acta Physicicochim (USSR) 16 132 13 Tanimoto K and Crooker P P 1984 Phys. Rev. A 29 1566-7 13 Tanimoto K, Crooker P P and Koch G C 1985 Phys. Rev. A 32 1893-5