Columnar phase
Encyclopedia
The columnar phase is a class of mesophase
s in which molecules assemble into cylindrical structures to act as mesogen
s. Originally, these kinds of liquid crystal
s were called discotic liquid crystals because the columnar structures are composed of flat-shaped discotic molecules stacked one-dimensionally. Since recent findings provide a number of columnar liquid crystals consisting of non-discoid mesogens, it is more common now to classify this state of matter and compounds with these properties as columnar liquid crystals.
Aida and co-workers recently reported cyclic peptides that self-assemble into polar columnar organizations. These materials can be unidirectionally aligned over large areas by application of an external electric field.
The discotic nematic phase includes nematic liquid crystals composed of flat-shaped discotic molecules without long-range order. In this phase, molecules do not form specific columnar assemblies but only float with their short axes in parallel to the director (a unit vector which defines the liquid-crystalline alignment and order).
. This molecule has one central benzene
ring surrounded by six alkyl
chains. Since then, a large number of discoid mesogen
ic compounds have been discovered in which triphenylene
, porphyrin
, phthalocyanine
, coronene
, and other aromatic molecules are involved. The typical columnar liquid-crystalline molecules have a pi-electron-rich aromatic core attached by flexible alkyl chains. This structure is attracting particular attention for potential molecular electronics in which aromatic parts transport electrons or holes and alkyl chains act as insulating parts. The advantages of liquid-crystalline conductors are their anisotropy, processibility, and self-healing characteristics for structural defects.
Mesophase
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...
s in which molecules assemble into cylindrical structures to act as 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. Originally, these kinds of 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 were called discotic liquid crystals because the columnar structures are composed of flat-shaped discotic molecules stacked one-dimensionally. Since recent findings provide a number of columnar liquid crystals consisting of non-discoid mesogens, it is more common now to classify this state of matter and compounds with these properties as columnar liquid crystals.
Aida and co-workers recently reported cyclic peptides that self-assemble into polar columnar organizations. These materials can be unidirectionally aligned over large areas by application of an external electric field.
Classes of Columnar Phases
Columnar liquid crystals are grouped by their structural order and the ways of packing of the columns. Nematic columnar liquid crystals have no long-range order and are less organized than other columnar liquid crystals. Other columnar phases with long-range order are classified by their two-dimensional lattices: hexagonal, tetragonal, rectangular, and oblique phases.The discotic nematic phase includes nematic liquid crystals composed of flat-shaped discotic molecules without long-range order. In this phase, molecules do not form specific columnar assemblies but only float with their short axes in parallel to the director (a unit vector which defines the liquid-crystalline alignment and order).
Current Topics of Interest
The first discotic liquid crystal was found in 1977 by the Indian researcher Sivaramakrishna ChandrasekharSivaramakrishna Chandrasekhar
Sivaramakrishna Chandrasekhar was an Indian physicist who won the Royal Medal in 1994. He was the founder-president of the International Liquid Crystal Society....
. This molecule has one central benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
ring surrounded by six alkyl
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
chains. Since then, a large number of discoid 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...
ic compounds have been discovered in which triphenylene
Triphenylene
In chemistry, the organic compound triphenylene is a flat polycyclic aromatic hydrocarbon consisting of four fused benzene rings. Triphenylene can be isolated from coal tar, but it is also made synthetically using benzyn chemistry. One molecule of triphenylene has delocalized 18-π-electron systems...
, porphyrin
Porphyrin
Porphyrins are a group of organic compounds, many naturally occurring. One of the best-known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein hemoglobin. Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at...
, phthalocyanine
Phthalocyanine
Phthalocyanine is an intensely blue-green coloured macrocyclic compound that is widely used in dyeing. Phthalocyanines form coordination complexes with most elements of the periodic table...
, coronene
Coronene
Coronene is a polycyclic aromatic hydrocarbon comprising six peri-fused benzene rings. Its chemical formula is . It is a yellow material that dissolves in such solvents as benzene, toluene, and dichloromethane. Its solutions emit blue light fluorescence under UV light...
, and other aromatic molecules are involved. The typical columnar liquid-crystalline molecules have a pi-electron-rich aromatic core attached by flexible alkyl chains. This structure is attracting particular attention for potential molecular electronics in which aromatic parts transport electrons or holes and alkyl chains act as insulating parts. The advantages of liquid-crystalline conductors are their anisotropy, processibility, and self-healing characteristics for structural defects.