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 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). Viewed in a microscope under polarized light illumination, a liquid crystal material 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 lyotrophic 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. Wikipedia does not have an article with this exact name. ...
Wikipedia does not have an article with this exact name. ...
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 assume the shape of its container. ...
Quartz crystal 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 division 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 and scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ...
This article treats polarization in electrodynamics. ...
Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ...
In physics, a phase transition is the transformation of a thermodynamic system from one phase to another. ...
Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ...
This page refers to concentration in the chemical sense. ...
Molecules that exhibit liquid crystal phases are called 'mesogens.' For a molecule to display an LC phase, it must generally be rigid and anisotropic (i.e. longer in one direction than another). Most mesogens fall into the 'rigid-rod' class, although disk-like mesogens are also known. Anisotropic (meaning non- isotropic) is usually used to describe a directionally dependent phenomenon. ...
Liquid crystal phases
The various LC phases 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 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. The orientational order may be quasicrystalline. 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 are randomly distributed as in a liquid, but they all point in the same direction (within each domain). The smectic phase is one where in addition to orientation order, the mesogens are grouped into layers, enforcing long-range positional order in one direction. In the smetic A phase, the molecules point perpendicular to the layer planes, whereas in the smectic C phase, the molecules are tilted with respect to the layer planes. Macroscopic means measurable and observable by the naked eye; describes existence as we perceive it. ...
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 subset of the phases of matter, fluids include liquids, gases, plasmas and, to some extent, plastic solids. ...
Anisotropic (meaning non- isotropic) is usually used to describe a directionally dependent phenomenon. ...
The structure of a thing is how the parts of it relate to each other, how it is put together. This contrast with process, which is how the thing works; but process requires a viable structure. ...
Quasicrystals are a peculiar form of solid in which the atoms of the solid are arranged in a seemingly regular, yet non-repeating structure. ...
In nematic liquid crystals the centers of gravity of molecules have no long-range order. ...
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 or 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 means measurable and observable by the naked eye; describes existence as we perceive it. ...
Quartz crystal 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. ...
A solid is a state of matter, characterized by a definite volume and a definite shape (i. ...
In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ...
Dimension (from Latin measured out) is, in essence, the number of degrees of freedom available for movement in a space. ...
Mesogens Liquid crystal mesogens are divided into two groups depending on the shape of the molecules. Calamitic liquid crystals consists of rod-like molecules and have order in the direction of the longer axes of the molecules. In contrast, discotic liquid crystals are composed of flat-shaped molecules which align in the direction of the shorter axes of the molecules.
Important types of calamitic liquid crystals include
Important types of discotic liquid crystals include In nematic liquid crystals the centers of gravity of molecules have no long-range order. ...
A biaxial nematic is a spatially homogeneous liquid crystal with three distinct optical axes. ...
Quasicrystals are a peculiar form of solid in which the atoms of the solid are arranged in a seemingly regular, yet non-repeating structure. ...
Biological membranes are a form of liquid crystal. Their rod-like molecules (e.g., phospholipids) are organized perpendicularly to the membrane surface, yet the membrane is fluid and elastic. It can also host important proteins such as receptors freely "floating" inside, or partly outside, the membrane. The columnar phase is a class of liquid-crystalline phases in which molecules assemble into cylindrical structures to act as mesogens. ...
The columnar phase is a class of liquid-crystalline phases in which molecules assemble into cylindrical structures to act as mesogens. ...
A biological membrane or biomembrane is a membrane which acts as a barrier within or around a cell. ...
Two schematic representations of a phospholipid. ...
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 the presence of electric field, these molecules align with the electric field, altering polarization of the light in a certain way. LCD redirects here. ...
See also list of optical topics. ...
In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ...
This article treats polarization in electrodynamics. ...
Lyotropic liquid crystals A lyotropic liquid crystal is a group of liquid-crystalline assemblies that consists of two or more components and exhibits 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 solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ...
Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ...
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.
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. 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 as follows:
- 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)
The same 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. ...
These lyotropic liquid-crystalline nanostructures are abundant in living systems such as DNA, polypeptides, and cell membranes. Accordingly, lyotropic liquid crystals attract particular attention in the field of biomimetic chemistry. Space-filling model of a section of DNA molecule Deoxyribose nucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ...
Peptides (from the Greek πεπτος, digestable), are the family of molecules formed from the linking, in a defined order, of various amino acids. ...
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. ...
Effect of chirality When the molecules that form liquid crystals have asymmetric carbon atoms and when the system has not chirality but racemic modification, the orientation vector of the molecular axis of the liquid crystals changes continuously and a macroscopic spiral structure appears in the system as a result. The cycle of the spiral structure is different for each molecule, but each molecule has the property that it reflects the light corresponding to its cycle. From this property, the liquid crystals change color when the cycle of the spiral structure agrees with the visible rays of light. Some kinds of liquid crystals change the cycle of their spiral structure when the temperature changes. This principle is applied in liquid crystal thermometers. In chemistry, a molecule is chiral if is not superimposable on its mirror image regardless of how it is contorted. ...
In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecules. ...
Nematic liquid crystals, which have spiral structures, are called cholesteric liquid crystals. Cholesteric liquid crystals are not distinguished from nematic liquid crystals thermodynamically; hence cholesteric liquid crystals are sometimes called chiral nematic liquid crystals.
Although almost all chiral liquid crystals include asymmetric carbon atoms in their molecules, it has recently been discovered that macroscopic chirality appears in liquid crystals that consist of bent-core molecules which do not have asymmetric carbon atoms. However, the appearance mechanism of this macroscopic chirality is not yet clear. General Name, Symbol, Number Carbon, C, 6 Chemical series Nonmetals Group, Period, Block 14 (IVA), 2, p Density, Hardness 2267 kg/m3 0. ...
In chemistry, a molecule is chiral if is not superimposable on its mirror image regardless of how it is contorted. ...
In chemistry, a molecule is chiral if is not superimposable on its mirror image regardless of how it is contorted. ...
See also Thermochromics are temperature sensitive inks, developed in the 1970s, that temporarily change color with exposure to temperature. ...
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References - de Gennes, P.G. and Prost, J. The Physics of Liquid Crystals, Claredon Press (1993).
- Chandrasekhar, S. Liquid Crystals 2ND edition, Cambridge Univ Pr Published (1993).
- Kleinert, H. and Maki, K., Lattice Textures in Cholesteric Liquid Crystals, Fortschritte Physik 29, 1 (1981) (http://www.physik.fu-berlin.de/~kleinert/kleiner_re75/75.pdf).
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