Mesophase
Encyclopedia
In physics
, a mesophase is a state of matter
intermediate between liquid
and solid
. Gelatin
is a common example of a partially-ordered structure in a mesophase. Further, biological structures such as the lipid bilayer
s of cell membrane
s exemplify the mesophase state.
Georges Friedel
(1922) called attention to the "mesomorphic states of matter" in his scientific assessment of observations of the so-called liquid crystal
s. Everyone knows a crystal
is solid and to crystallize is to make solid. The oxymoron
of the liquid crystal is resolved through the notion of mesophases. The observations noted an optic axis persisting in materials that had been melted
and had begun to flow. But the catch-phrase of the liquid crystal caught on, even when displaced in technical writing.
For example, in The Physics of Liquid Crystals the mesophases are introduced from the beginning:
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
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
s. The susceptibility of the optic axis, called a director, to an electric or magnetic field produces the potential for an optical switch. Methods used include the Freedericksz transition
and the twisted nematic field effect
. From early liquid crystal display
s 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
. Ultimately it is rendered to an isotropic state classically referred to as liquid. Mesophases occur before then when an intermediate state of order
is still maintained as in the nematic, smectic, and columnar phases of liquid crystals. Mesophases thus exhibit anisotropy
. For instance, LCD devices work on the optical switch principle that obscures light or lets it pass. This switch is turned off and on by an electric field
applied to the mesogen with director. The response of the director to the field is expressed with viscosity
parameters, as in the Ericksen-Leslie theory in continuum mechanics
developed by Jerald Ericksen
and Frank Matthews Leslie
.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, a mesophase is a state of matter
State of matter
States of matter are the distinct forms that different phases of matter take on. Solid, liquid and gas are the most common states of matter on Earth. However, much of the baryonic matter of the universe is in the form of hot plasma, both as rarefied interstellar medium and as dense...
intermediate between liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
and solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
. Gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
is a common example of a partially-ordered structure in a mesophase. Further, biological structures such as the lipid bilayer
Lipid bilayer
The lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. The cell membrane of almost all living organisms and many viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus...
s of cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
s exemplify the mesophase state.
Georges Friedel
Georges Friedel
Georges Friedel was a French mineralogist and crystallographer.- Life :Georges was the son of the famous chemist Charles Friedel...
(1922) called attention to the "mesomorphic states of matter" in his scientific assessment of observations of the so-called liquid crystal
Liquid crystal
Liquid crystals are a state of matter that have properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of LC phases, which can be...
s. Everyone knows a crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
is solid and to crystallize is to make solid. The oxymoron
Oxymoron
An oxymoron is a figure of speech that combines contradictory terms...
of the liquid crystal is resolved through the notion of mesophases. The observations noted an optic axis persisting in materials that had been melted
Melting
Melting, or fusion, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid...
and had begun to flow. But the catch-phrase of the liquid crystal caught on, even when displaced in technical writing.
For example, in The Physics of Liquid Crystals the mesophases are introduced from the beginning:
- ...certain organic materials do not show a single transition from solid to liquid, but rather a cascade of transitions involving new phases. The mechanical properties and the symmetry 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
Mesogen
Mesogen is the fundamental unit of a liquid crystal that induces structural order in the crystals.Typically, a liquid-crystalline molecule consists of a rigid moiety and one or more flexible parts. The rigid part aligns molecules in one direction, whereas the flexible parts induce fluidity in the...
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
Display device
A display device is an output device for presentation of information in visual or tactile form...
s. The susceptibility of the optic axis, called a director, to an electric or magnetic field produces the potential for an optical switch. Methods used include the Freedericksz transition
Fréedericksz transition
The Fréedericksz transition is a phase transition in liquid crystals produced when a sufficiently strong electric or magnetic field is applied to a liquid crystal in an undistorted state. Below a certain field threshold the director remains undistorted. As the field value is gradually increased...
and the twisted nematic field effect
Twisted nematic field effect
The twisted nematic effect was a main technology breakthrough that made liquid crystal displays practical. Unlike earlier displays, TN-cells did not require a current to flow for operation and used low operating voltages suitable for use with batteries...
. From early liquid crystal display
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
s 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
Melting, or fusion, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid...
. Ultimately it is rendered to an isotropic state classically referred to as liquid. Mesophases occur before then when an intermediate state of order
Order and disorder (physics)
In physics, the terms order and disorder designate the presence or absence of some symmetry or correlation in a many-particle system.In condensed matter physics, systems typically are ordered at low temperatures; upon heating, they undergo one or several phase transitions into less ordered...
is still maintained as in the nematic, smectic, and columnar phases of liquid crystals. Mesophases thus exhibit anisotropy
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
. For instance, LCD devices work on the optical switch principle that obscures light or lets it pass. This switch is turned off and on by an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
applied to the mesogen with director. The response of the director to the field is expressed with viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
parameters, as in the Ericksen-Leslie theory in continuum mechanics
Continuum mechanics
Continuum mechanics is a branch of mechanics that deals with the analysis of the kinematics and the mechanical behavior of materials modelled as a continuous mass rather than as discrete particles...
developed by Jerald Ericksen
Jerald Ericksen
Jerald LaVerne Ericksen is an American mathematician specializing in continuum mechanics.Jerald was born 20 December 1924 in Portland, Oregon. His father Adolf worked at a Portland creamery and became adept at judging the quality of butter. Later his father acquired a small creamery in Vancouver,...
and Frank Matthews Leslie
Frank Matthews Leslie
Frank Matthews Leslie FRS was a mathematical physicist specializing in continuum mechanics. He is remembered for the Ericksen–Leslie theory he developed with Jerald Ericksen to describe the viscosity of mesophases associated with liquid crystals. The parameters of this theory are viscosities called...
.
External links
- Springer Verlag Partially-Ordered Systems ISSN 0941-5114 .