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Encyclopedia > Liquid crystal
Schlieren texture of Liquid Crystal nematic phase

Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal. For instance, a liquid crystal (LC) may flow like a liquid, but have the molecules in the liquid arranged and/or oriented in a crystal-like way. There are many different types of LC phases, which can be distinguished based on their different optical properties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have a distinct texture. Each 'patch' in the texture corresponds to a domain where the LC molecules are oriented in a different direction. Within a domain, however, the molecules are well ordered. Liquid crystal materials may not always be in an LC phase (just as water is not always in the liquid phase: it may also be found in the solid or gas phase). Liquid crystals can be divided into thermotropic and lyotropic LCs. Thermotropic LCs exhibit a phase transition into the LC phase as temperature is changed, whereas lyotropic LCs exhibit phase transitions as a function of concentration of the mesogen in a solvent (typically water) as well as temperature. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... Schlieren are optical inhomogeneities in transparent material not visible to the human eye. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... A liquid will usually assume the shape of its container. ... Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... A microscope (Greek: (micron) = small + (skopein) = to look at) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... Hahahahahahahahahahahahhahahahahahahahahahahahahahahahahahahahahahhahaahahhhahhhahaahhhahahahahahahahahahahahahahahahahahahahahahahahahahahahhahahahahahaahhaaahahahahahahahahahahahahhahahahahahahahhahahahahahahahahahahahahahahahahhahahahahahhahahahhahahahhahahahahahhahahahhahahahhahahahhahahahahahahahahahhahahaahhaahahhaahhahaahahahahhahaahahsahahahahahshhsshshshagagaggagagagagagaggagagahahahahhahahahahahahahahahahahahhahahahahahahahahhahahahahahahahahahahyhahahahahhahaahahahahahahahahahahhahahahaah! your moma is a hoe. ... A liquid crystal ( LC ) is thermotropic if the order of its components is determined or changed with temperature. ... A liquid crystalline material is called lyotropic if the ordering effects in it are induced by changing its concentration within a solvent. ... In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ... Fig. ... In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. ... Mesogen is the fundamental unit of a liquid crystal that induces structural order in the crystals. ... Fig. ...

## Mesogens

Molecules that exhibit liquid crystal phases are called mesogens. For a molecule to display an LC phase, it must generally be fairly rigid and anisotropic (i.e. longer in one direction than another). Most mesogens fall into the 'rigid-rod' class (calamitic mesogens), which orient based on their long axis. Disk-like (discotic) mesogens are also known, and these orient in the direction of their short axis. In addition to molecules, polymers and colloidal suspensions can also form LC phases. For instance, micrometre-sized objects (such as anisotropic colloids, latex particles, clay platelets, and even some viruses, such as the tobacco mosaic virus) can organize themselves in liquid crystal phases. These more exotic mesogens generally fall into the category of lyotropic liquid crystals. This article is being considered for deletion in accordance with Wikipedias deletion policy. ... The columnar phase is a class of liquid-crystalline phases in which molecules assemble into cylindrical structures to act as mesogens. ... The metre, or meter (U.S.), is a measure of length. ... Stop editing pages god ... The Tobacco mosaic virus (TMV) is an RNA virus that infects plants, especially tobacco and other members of the family Solanaceae, showing characteristic patterns (mottling and discoloration) on the leaves (thus the name). ...

## Liquid crystal phases

The various LC phases (called mesophases) can be characterized by the type of ordering that is present. One can distinguish positional order (whether or not molecules are arranged in any sort of ordered lattice) and orientational order (whether or not molecules are mostly pointing in the same direction), and moreover order can be either short-range (only between molecules close to each other) or long-range (extending to larger, sometimes macroscopic, dimensions). Most thermotropic LCs will have an isotropic phase at high temperature. That is, heating will eventually drive them into a conventional liquid phase characterized by random and isotropic molecular ordering (little to no long-range order), and fluid-like flow behavior. Under other conditions (for instance, lower temperature), an LC might inhabit one or more phases with significant anisotropic orientational structure and long-range orientational order while still having an ability to flow. Macroscopic is commonly used to describe physical objects that are measurable and observable by the naked eye. ... Isotropic means independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... Look up Structure in Wiktionary, the free dictionary. ...

The ordering of liquid crystalline phases is extensive on the molecular scale. This order extends up to the entire domain size, which may be on the order of micrometres, but usually does not extend to the macroscopic scale as often occurs in classical crystalline solids. However, some techniques (such as the use of boundaries or an applied electric field) can be used to enforce a single ordered domain in a macroscopic liquid crystal sample. The ordering in a liquid crystal might extend along only one dimension, with the material being essentially disordered in the other two directions. Macroscopic is commonly used to describe physical objects that are measurable and observable by the naked eye. ... Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... It has been suggested that optical field be merged into this article or section. ... :For other senses of this word, see dimension (disambiguation). ...

### Thermotropic liquid crystals

Thermotropic phases are those that occur in a certain temperature range. If the temperature is raised too high, thermal motion will destroy the delicate cooperative ordering of the LC phase, pushing the material into a conventional isotropic liquid phase. At too low a temperature, most LC materials will form a conventional (though anisotropic) crystal. Many thermotropic LCs exhibit a variety of phases as temperature is changed. For instance, a particular mesogen may exhibit various smectic and nematic (and finally isotropic) phases as temperature is increased.

#### Nematic phase

One of the most common LC phases is the nematic, where the molecules have no positional order, but they do have long-range orientational order. Thus, the molecules flow and their centre of mass positions are randomly distributed as in a liquid, but they all point in the same direction (within each domain). Most nematics are uniaxial: they have one axis that is longer and preferred, with the other two being equivalent (can be approximated as cylinders). Some liquid crystals are biaxial nematics, meaning that in addition to orienting their long axis, they also orient along a secondary axis. To meet Wikipedias quality standards, this article or section may require cleanup. ... A biaxial nematic is a spatially homogeneous liquid crystal with three distinct optical axes. ...

Liquid crystals are a phase of matter whose order is intermediate between that of a liquid and that of a crystal. The molecules are typically rod-shaped organic moieties about 25 angstroms (2.5 nanometers) in length and their ordering is a function of temperature. The nematic phase, for example, is characterized by the orientational order of the constituent molecules. The molecular orientation (and hence the material's optical properties) can be controlled with applied electric fields. Nematics are (still) the most commonly used phase in liquid crystal displays (LCDs), with many such devices using the twisted nematic geometry. The smectic phases, which are found at lower temperatures than the nematic, form well-defined layers that can slide over one another like soap. The smectics are thus positionally ordered along one direction. In the Smectic A phase, the molecules are oriented along the layer normal, while in the Smectic C phase they are tilted away from the layer normal. These phases, which are liquid-like within the layers, are illustrated below. There is a very large number of different smectic phases, all characterized by different types and degrees of positional and orientational order. An angstrom, angstrÃ¶m, or Ã¥ngstrÃ¶m (symbol Ã…) is a unit of length. ... A nanometre (American spelling: nanometer) is 1. ... Schlieren texture of Liquid Crystal nematic phase Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal. ...

#### Chiral phases

The chiral nematic phase exhibits chirality (handedness). This phase is often called the cholesteric phase because it was first observed for cholesterol derivatives. Only chiral molecules (i.e.: those that lack inversion symmetry) can give rise to such a phase. This phase exhibits a twisting of the molecules along the director, with the molecular axis perpendicular to the director. The finite twist angle between adjacent molecules is due to their asymmetric packing, which results in longer-range chiral order. In the smectic C* phase, the molecules orient roughly along the director, with a finite tilt angle, and a twist relative to other mesogens. This results in, again, a spiral twisting of molecular axis along the director. To meet Wikipedias quality standards, this article or section may require cleanup. ... The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Cholesterol is a sterol (a combination steroid and alcohol) and a lipid found in the cell membranes of all body tissues, and transported in the blood plasma of all animals. ... The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ...

The chiral pitch refers to the distance (along the director) over which the mesogens undergo a full 360° twist (but note that the structure repeats itself every half-pitch, since the positive and negative directions along the director are equivalent). The pitch may be varied by adjusting temperature or adding other molecules to the LC fluid. For many types of liquid crystals, the pitch is on the same order as the wavelength of visible light. This causes these systems to exhibit unique optical properties, such as selective reflection. These properties are exploited in a number of optical applications. The wavelength is the distance between repeating units of a wave pattern. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ...

#### Discotic phases

Disk-shaped mesogens can orient themselves in a layer-like fashion known as the discotic nematic phase. If the disks pack into stacks, the phase is called a discotic columnar. The columns themselves may be organized into rectangular or hexagonal arrays. Chiral discotic phases, similar to the chiral nematic phase, are also known. The columnar phase is a class of liquid-crystalline phases in which molecules assemble into cylindrical structures to act as mesogens. ...

### Lyotropic liquid crystals

A lyotropic liquid crystal consists of two or more components that exhibit liquid-crystalline properties in certain concentration ranges. In the lyotropic phases, solvent molecules fill the space around the compounds to provide fluidity to the system. In contrast to thermotropic liquid crystals, these lyotropics have another degree of freedom of concentration that enables them to induce a variety of different phases. A liquid crystalline material is called lyotropic if the ordering effects in it are induced by changing its concentration within a solvent. ... A solvent is a fluid phase (liquid, gas, or plasma) that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... The pitch drop experiment at the University of Queensland. ...

A compound which has two immiscible hydrophilic and hydrophobic parts within the same molecule is called an amphiphilic molecule. Many amphiphilic molecules show lyotropic liquid-crystalline phase sequences depending on the volume balances between the hydrophilic part and hydrophobic part. These structures are formed through the micro-phase segregation of two incompatible components on a nanometer scale. Soap is an everyday example of a lyotropic liquid crystal. The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... An amphipathic (a. ...

The content of water or other solvent molecules changes the self-assembled structures. At very low amphiphile concentration, the molecules will be dispersed randomly without any ordering. At slightly higher (but still low) concentration, amphiphilic molecules will spontaneously assemble into micelles or vesicles. This is done so as to 'hide' the hydrophobic tail of the amphiphile inside the micelle core, exposing a hydrophilic (water-soluble) surface to aqueous solution. These spherical objects do not order themselves in solution, however. At higher concentration, the assemblies will become ordered. A typical phase is a hexagonal columnar phase, where the amphiphiles form long cylinders (again with a hydrophilic surface) that arrange themselves into a roughly hexagonal lattice. This is called the middle soap phase. At still higher concentration, a lamellar phase (neat soap phase) may form, wherein extended sheets of amphiphiles are separated by thin layers of water. For some systems, a cubic (also called viscous isotropic) phase may exist between the hexagonal and lamellar phases, wherein spheres are formed that create a dense cubic lattice. These spheres may also be connected to one another, forming a bicontinuous cubic phase. Schematic of a micelle. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...

The objects created by amphiphiles are usually spherical (as in the case of micelles), but may also be disc-like (bicelles), rod-like, or biaxial (all three micelle axes are distinct). These anisotropic self-assembled nano-structures can then order themselves in much the same way as liquid crystals do, forming large-scale versions of all the thermotropic phases (such as a nematic phase of rod-shaped micelles).

For some systems, at high concentration, inverse phases are observed. That is, one may generate an inverse hexagonal columnar phase (columns of water encapsulated by amphiphiles) or an inverse micellar phase (a bulk liquid crystal sample with spherical water cavities).

A generic progression of phases, going from low to high amphiphile concentration, is:

• Discontinuous cubic phase (micellar phase)
• Hexagonal columnar phase (middle phase)
• Bicontinuous cubic phase
• Lamellar phase
• Bicontinuous cubic phase
• Reverse hexagonal columnar phase
• Inverse cubic phase (Inverse micellar phase)

Even within the same phases, their self-assembled structures are tunable by the concentration: for example, in lamellar phases, the layer distances increase with the solvent volume. Since lyotropic liquid crystals rely on a subtle balance of intermolecular interactions, it is more difficult to analyze their structures and properties than those of thermotropic liquid crystals.

Similar phases and characteristics can be observed in immiscible diblock copolymers. A heteropolymer, also called a copolymer, is a polymer formed when two different types of monomer are linked in the same polymer chain. ...

### Metallotropic liquid crystals

Liquid crystal phases can also be based on low-melting inorganic phases like ZnCl2 that have a structure formed of linked tetrahedra and easily form glasses. The addition of long chain soaplike molecules leads to a series of new phases that show a variety of liquid crystalline behavior both as a function of the inorganic-organic composition ratio and of temperature. This class of materials has been named metallotropic J.D. Martin et al.

## Biological liquid crystals

Lyotropic liquid-crystalline nanostructures are abundant in living systems. Accordingly, lyotropic liquid crystals attract particular attention in the field of biomimetic chemistry. In particular, biological membranes and cell membranes are a form of liquid crystal. Their constituent rod-like molecules (e.g., phospholipids) are organized perpendicularly to the membrane surface, yet the membrane is fluid and elastic. The constituent molecules can flow in-plane quite easily, but tend not to leave the membrane, and can flip from one side of the membrane to the other with some difficulty. These liquid crystal membrane phases can also host important proteins such as receptors freely "floating" inside, or partly outside, the membrane. A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that encapsulate the cell. ... Two schematic representations of a phospholipid. ...

Many other biological structures exhibit LC behavior. For instance, the concentrated protein solution that is extruded by a spider to generate silk is, in fact, a liquid crystal phase. The precise ordering of molecules in silk is critical to its renowned strength. DNA and many polypeptides can also form LC phases. Since biological mesogens are usually chiral, chirality often plays a role in these phases. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Spider silk is a fibre secreted by spiders. ... The structure of part of a DNA double helix. ... Peptides (from the Greek Ï€ÎµÏ€Ï„Î¿Ï‚, digestible), are the family of short molecules formed from the linking, in a defined order, of various Î±-amino acids. ...

## Theoretical treatment of liquid crystals

Microscopic theoretical treatment of fluid phases can become quite involved, owing to the high material density, which means that strong interactions, hard-core repulsions, and many-body correlations cannot be ignored. In the case of liquid crystals, anisotropy in all of these interactions further complicate analysis. There are a number of fairly simple theories, however, that can at least predict the general behavior of the phase transitions in liquid crystal systems.

### Order parameter

The description of liquid crystals involves an analysis of order. To make this quantitative, an orientational order parameter is usually defined based on the average of the second Legendre polynomial: Note: The term Legendre polynomials is sometimes used (wrongly) to indicate the associated Legendre polynomials. ...

$S = langle P_2(cos theta) rangle = left langle frac{3 cos^2 theta-1}{2} right rangle$

where θ is the angle between the mesogen molecule axis and the local director (which is the 'preferred direction' in a liquid crystal sample). This definition is convenient, since for a completely random and isotropic sample, S=0, whereas for a perfectly aligned sample S=1. For a typical liquid crystal sample, S is on the order of 0.3 to 0.8, and generally decreases as the temperature is raised. In particular, a sharp drop of the order parameter to 0 is observed when one undergoes a phase transition from an LC phase into the isotropic phase. The order parameter can be measured experimentally in a number of ways. For instance, diamagnetism, birefringence, Raman scattering, and NMR can also be used to determine S. Brugmans (in 1778) was the first person to observe that certain materials were repelled by magnetic fields. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Raman scattering or the Raman effect is the inelastic scattering of a photon which creates or annihilates an optical phonon. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ...

One could also characterize the order of a liquid crystal using other even Legendre polynomials (all the odd polynomials average to zero since the director can point in either of two antiparallel directions). These higher-order averages are more difficult to measure, but can yield additional information about molecular ordering.

### Onsager hard-rod model

A very simple model which predicts lyotropic phase transitions is the hard-rod model proposed by Lars Onsager. This theory considers the volume excluded from the center-of-mass of one idealized cylinder as it approaches another. Specifically, if the cylinders are oriented parallel to one another, there is very little volume that is excluded from the center-of-mass of the approaching cylinder (it can come quite close to the other cylinder). If, however, the cylinders are at some angle to one another, then there is a large volume surrounding the cylinder where the approaching cylinder's center-of-mass cannot enter (due to the hard-rod repulsion between the two idealized objects). Thus, this angular arrangement sees a decrease in the net positional entropy of the approaching cylinder (there are fewer states available to it). Lars Onsager (November 27, 1903 â€“ October 5, 1976) was a Norwegian physical chemist, winner of the 1968 Nobel Prize in Chemistry. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ...

The fundamental insight here is that, while parallel arrangements of anisotropic objects leads to a decrease in orientational entropy, there is an increase in positional entropy. Thus in some case greater positional order will be entropically favorable. This theory thus predicts that a solution of rod-shaped objects will undergo a phase transition, at sufficient concentration, into a nematic phase. Recently this theory is used to observe the phase transition between nematic and smectic-A at very high concentration also Hanif et al.. Although this model is conceptually helpful, its mathematical formulation makes several assumptions that limit its applicability to real systems.

### Maier-Saupe mean field theory

This statistical theory includes contributions from an attractive intermolecular potential. The anisotropic attraction stabilizes parallel alignment of neighboring molecules, and the theory then considers a mean-field average of the interaction. Solved self-consistently, this theory predicts thermotropic phase transitions, consistent with experiment. A many-body system with interactions is generally very difficult to solve exactly, except for extremely simple cases (Gaussian field theory, 1D Ising model. ...

### Elastic continuum theory

In this formalism, a liquid crystal material is treated as a continuum; molecular details are entirely ignored. Rather, this theory considers perturbations to a presumed oriented sample. One can identify three types of distortions that could occur in an oriented sample: (1) twists of the material, where neighboring molecules are forced to be angled with respect to one another, rather than aligned; (2) splay of the material, where bending occurs perpendicular to the director; and (3) bend of the material, where the distortion is parallel to the director and mesogen axis. All three of these types of distortions incur an energy penalty. They are defects that often occur near domain walls or boundaries of the enclosing container. The response of the material can then be decomposed into terms based on the elastic constants corresponding to the three types of distortions.

## Effect of chirality

As already described, chiral mesogens usually give rise to chiral mesophases. For molecular mesogens, this means that the molecule must possess an asymmetric carbon atom. An additional requirement is that the system not be racemic: a mixture of right- and left-handed versions of the mesogen will cancel the chiral effect. Due to the cooperative nature of liquid crystal ordering, however, a small amount of chiral dopant in an otherwise achiral mesophase is often enough to select out one domain handedness, making the system overall chiral. The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ...

Chiral phases usually have a helical twisting of the mesogens. If the pitch of this twist is on the order of the wavelength of visible light, then interesting optical interference effects will be observed. The chiral twisting that occurs in chiral LC phases also makes the system respond differently to right- and left-handed circularly polarized light. These materials can thus be used as polarization filters.

It is possible for chiral mesogens to produce essentially achiral mesophases. For instance, in certain ranges of concentration and molecular weight, DNA will form an achiral line hexatic phase. A curious recent observation is of the formation of chiral mesophases from achiral mesogens. Specifically, bent-core molecules (sometimes called banana liquid crystals) have been shown to form liquid crystal phases that are chiral. In any particular sample, various domains will have opposite handedness, but within any given domain, strong chiral ordering will be present. The appearance mechanism of this macroscopic chirality is not yet entirely clear. It appears that the molecules stack in layers and orient themselves in a tilted fashion inside the layers. These liquid crystals phases are ferroelectric and anti-ferroelectric, both of which are of interest for applications. The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ...

## Applications of liquid crystals

Liquid crystals find wide use in liquid crystal displays, which rely on the optical properties of certain liquid crystalline molecules in the presence or absence of an electric field. In a typical device, a liquid crystal layer sits between two polarizers that are crossed (oriented at 90° to one another). The liquid crystal is chosen so that its relaxed phase is a twisted one. This twisted phase reorients light that has passed through the first polarizer, allowing it to be transmitted through the second polarizer and reflected back to the observer. The device thus appears clear. When an electric field is applied to the LC layer, all the mesogens align (and are no longer twisting). In this aligned state, the mesogens do not reorient light, so the light polarized at the first polarizer is absorbed at the second polarizer, and the entire device appears dark. In this way, the electric field can be used to make a pixel switch between clear or dark on command. Color LCD systems use the same technique, with color filters used to generate red, green, and blue pixels. Similar principles can be used to make other liquid crystal based optical devices. Reflective twisted nematic liquid crystal display. ... Table of Opticks, 1728 Cyclopaedia Optics ( appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... It has been suggested that optical field be merged into this article or section. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ...

Thermotropic chiral LCs whose pitch varies strongly with temperature can be used as crude thermometers, since the color of the material will change as the pitch is changed. Liquid crystal color transitions are used on many aquarium and pool thermometers. Other liquid crystal materials change color when stretched or stressed. Thus, liquid crystal sheets are often used in industry to look for hot spots, map heat flow, measure stress distribution patterns, and so on. Liquid crystal in fluid form is used to detect electrically generated hot spots for failure analysis in the semiconductor industry. Liquid crystal memory units with extensive capacity were used in Space Shuttle navigation equipment. Failure analysis is the process of determining the cause of failure, collecting and analyzing data, and developing conclusions to eliminate the failure mechanism causing specific device or system failures. ... A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ...

It is also worth noting that many common fluids are in fact liquid crystals. Soap, for instance, is a liquid crystal, and forms a variety of LC phases depending on its concentration in water.

Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Thermochromics are temperature sensitive inks, developed in the 1970s, that temporarily change color with exposure to temperature. ... In a chromonic, relatively flat molecules form linear aggregates. ... // Background: Liquid Crystal Polymers (LCP) are a unique class of wholly aromatic polyester polymers that provide previously unavailable high performance properties. ...

## References

• de Gennes, P.G. and Prost, J (1993). The Physics of Liquid Crystals. Oxford: Clarendon Press. ISBN 0-19-852024-7.
• Chandrasekhar, S. (1992). Liquid Crystals, 2nd edition, Cambridge: Cambridge University Press. ISBN 0-521-41747-3 (hardback) ISBN 0-521-42741-X (pbk.).
• Kleinert, H. and Maki, K (1981). "Lattice Textures in Cholesteric Liquid Crystals". Fortschritte Physik 29 (1).
• Collings, P.J. and Hird, M (1997). Introduction to Liquid Crystals. Bristol, PA: Taylor & Francis. ISBN 0-7484-0643-3 (hardback) ISBN 0-7484-0483-X (pbk.).
• James D. Martin, Cristin L. Keary, Todd A. Thornton, Mark P. Novotnak, Jeremey W. Knutson and Jacob C. W. Folmer (2006). "Metallotropic liquid crystals formed by surfactant templating of molten metal halides". Nature Materials 5: 271–275.
• Hanif Bayat Movahed, Raul Cruz Hidalgo and D. E. Sullivan (March 2006). "The phase transitions of semiflexible hard sphere chains liquid". 73, 032701.

Pierre-Gilles de Gennes (born October 24, 1932) is a French physicist and Nobel laureate. ... This article is about the Indian-American physicist. ... Hagen Kleinert, Photo taken in 2004 Hagen Kleinert is the Professor of Theoretical Physics at the Free University of Berlin, Germany, and Honorary Member of the Russian Academy of Creative Endeavors. ...

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