chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

and

chemical physics Chemical physics is a subdiscipline of chemistry and physics that investigates physicochemical phenomena using techniques from atomic and molecular physics and condensed matter physics; it is the branch of physics that studies chemical process ...

, a mesophase is a

state of matter In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many intermediate states are known to exist, such as liquid crystal ...

intermediate between

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

and

solid Solid is one of the State of matter#Four fundamental states, four fundamental states of matter (the others being liquid, gas, and Plasma (physics), plasma). The molecules in a solid are closely packed together and contain the least amount o ...

. Gelatin is a common example of a partially ordered structure in a mesophase. Further, biological structures such as the

lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...

s of

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

s are examples of mesophases. Georges Friedel (1922) called attention to the "mesomorphic states of matter" in his scientific assessment of observations of the so-called

liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. T ...

s. Conventionally a

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

is solid, and

crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...

converts liquid to solid. The oxymoron of the liquid crystal is resolved through the notion of mesophases. The observations noted an

optic axis An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light propagat ...

persisting in materials that had been melted and had begun to flow. The term ''liquid crystal'' persists as a

colloquialism Colloquialism (), also called colloquial language, everyday language or general parlance, is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom norm ...

, but use of the term was criticized in 1993: In ''The Physics of Liquid Crystals''P.G. de Gennes & J. Prost (1993) ''The Physics of Liquid Crystals'', 2nd edition,

Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...

the mesophases are introduced from the beginning: :...certain

organic materials Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...

do not show a single transition from solid to liquid, but rather a cascade of transitions involving new phases. The

mechanical properties A materials property is an intensive property of a material, i.e., a physical property that does not depend on the amount of the material. These quantitative properties may be used as a metric by which the benefits of one material versus another ...

and the

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

properties of these phases are intermediate between those of a liquid and those of a crystal. For this reason they have often been called ''liquid crystals''. A more proper name is ‘mesomorphic phases’ (''mesomorphic'': intermediate form) Further, "The classification of mesophases (first clearly set out by G. Friedel in 1922) is essentially based on symmetry." Molecules that demonstrate mesophases are called

mesogen A mesogen is a compound that displays liquid crystal properties. Mesogens can be described as disordered solids or ordered liquids because they arise from a unique state of matter that exhibits both solid- and liquid-like properties called the li ...

s. In technology, molecules in which the optic axis is subject to manipulation during a mesophase have become commercial products as they can be used to manufacture

display device A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signal the ...

s, known as

liquid-crystal display A liquid-crystal display (LCD) is a flat-panel display A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipmen ...

s (LCDs). The susceptibility of the optical axis, called a ''director'', to an electric or magnetic field produces the potential for an optical switch that obscures light or lets it pass. Methods used include the Freedericksz transition, the

twisted nematic field effect The twisted nematic effect (''TN-effect'') was a main technology breakthrough that made LCDs practical. Unlike earlier displays, TN-cells did not require a current to flow for operation and used low operating voltages suitable for use with batter ...

and the in-plane switching effect. From early liquid crystal displays the buying public has embraced the low-power optical switch facility of mesophases with director. Consider a solid consisting of a single molecular species and subjected to

melting Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which inc ...

. Ultimately it is rendered to an

isotropic Isotropy is uniformity in all orientations; it is derived . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe ...

state classically referred to as liquid. Mesophases occur before then when an intermediate state of order is still maintained as in the nematic,

smectic Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. The ...

, and

columnar Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

phases of liquid crystals. Mesophases thus exhibit

anisotropy Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...

. LCD devices work as an optical switch which is turned off and on by an

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

applied to the mesogen with director. The response of the director to the field is expressed with

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

parameters, as in the Ericksen-Leslie theory in

continuum mechanics Continuum mechanics is a branch of mechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as discrete particles. The French mathematician Augustin-Louis Cauchy was the first to formulate such m ...

developed by

Jerald Ericksen Jerald LaVerne Ericksen (December 20, 1924 – June 11, 2021) was an American mathematician specializing in continuum mechanics. Biography Ericksen was born in Portland, Oregon. His father Adolf worked at a Portland creamery and became adept a ...

and Frank Matthews Leslie. LCD devices work only up to the transition temperature when the mesophase changes to the isotropic liquid phase at the so-called ''clearing point''.''Definition of the clearing point.''
Goldbook IUPAC. Retrieved 16 February 2021. Mesophase phenomena are important in many scientific fields. The publishing arms of professional societies have academic journals as needed. For instance, the

American Chemical Society The American Chemical Society (ACS) is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 at New York University, the ACS currently has more than 155,000 members at all d ...

has both ''

Macromolecules A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The ...

'' and '' Langmuir'', while

Royal Society of Chemistry The Royal Society of Chemistry (RSC) is a learned society (professional association) in the United Kingdom with the goal of "advancing the chemistry, chemical sciences". It was formed in 1980 from the amalgamation of the Chemical Society, the Ro ...

has '' Soft Matter'', and

American Physical Society The American Physical Society (APS) is a not-for-profit membership organization of professionals in physics and related disciplines, comprising nearly fifty divisions, sections, and other units. Its mission is the advancement and diffusion of k ...

has ''

Physical Review E ''Physical Review E'' is a peer-reviewed, scientific journal, published monthly by the American Physical Society. The main field of interest is collective phenomena of many-body systems. It is currently edited by Uwe C. Täuber. While original r ...

'', and

Elsevier Elsevier () is a Dutch academic publishing company specializing in scientific, technical, and medical content. Its products include journals such as ''The Lancet'', ''Cell'', the ScienceDirect collection of electronic journals, '' Trends'', th ...

has ''

Advances in Colloid and Interface Science ''Advances in Colloid and Interface Science'' is a quarterly peer-reviewed scientific journal published by Elsevier. It covers all aspects of colloid and interface science, including surface chemistry, physical chemistry, and surface tension. Ab ...

''.

Notes and references

Sivaramakrishna Chandrasekhar Sivaramakrishna Chandrasekhar FNA, FRS (6 August 1930 – 8 March 2004) was an Indian physicist who won the Royal Medal in 1994. He was the founder-president of the International Liquid Crystal Society. Chandrasekhar was born on 6 August ...

(1992) ''Liquid Crystals'', 2nd edition,

Cambridge University Press Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by Henry VIII of England, King Henry VIII in 1534, it is the oldest university press A university press is an academic publishing hou ...

. * David Dunmur & Tim Sluckin (2011) ''Soap, Science, and Flat-screen TVs: a history of liquid crystals'',

. * J. Prost & C.E. Williams (1999) "Liquid Crystals: Between Order and Disorder", pp 289–315 in ''Soft Matter Physics'', Mohamed Daoud & Claudine E. Williams, editors, translated by Stephen N. Lyle from ''La Just Argile'' (1995), Springer Verlag {{ISBN, 3-540-64852-6 .

External links

Soft Matter World organization
*

Springer Verlag Springer Science+Business Media, commonly known as Springer, is a German multinational publishing company of books, e-books and peer-reviewed journals in science, humanities, technical and medical (STM) publishing. Originally founded in 1842 in ...

Partially Ordered Systems
ISSN 0941-5114 . Phases of matter Soft matter Phase transitions Liquid crystals Continuum mechanics

See also

Notes and references

External links