Lyotropic
Encyclopedia
A material is called lyotropic if it forms liquid crystal
phases because of the addition of a solvent
. Historically the term was used to describe materials composed of amphiphilic molecules. Such molecules comprise a water-loving 'hydrophilic' head-group (which may be ionic or non-ionic) attached to a water-hating 'hydrophobic' group. Typical hydrophobic groups are saturated or unsaturated hydrocarbon chains. Examples of amphiphilic compounds are the salts of fatty acids; phospholipids. Many simple amphiphiles are used as detergents. Lyotropic liquid crystal
phases in these materials are formed by a process of self-assembly that is driven by the hydrophobic effect
.
Lyotropic liquid crystal phases are formed on the dissolution of amphiphilic molecules of a material in a solvent. There are several different type of lyotropic liquid crystal structures. Each of these different types has a different extent of molecular ordering within the solvent matrix.
The term lyotropic has also been applied to the liquid crystalline phases that are formed by certain polymeric materials, particularly those consisting of rigid rod-like macromolecules, when they are mixed with appropriate solvents. Examples are suspensions
of rod-like virus
es as the Tobacco Mosaic Virus
as well as man-made colloid
al suspensions of non-spherical colloidal particles. Other examples include DNA
and Kevlar
, which dissolves in sulfuric acid
to give a lyotropic phase. It is noted that in these cases the solvent acts to lower the melting point of the materials thereby enabling the liquid crystalline phases to be accessible. These liquid crystalline phases are closer in architecture to thermotropic
liquid crystalline phases than to the conventional lyotropic phases. In contrast to the behaviour of amphiphilic molecules, the lyotropic behaviour of the rod-like molecules does not involve self-assembly.
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...
phases because of the addition of a solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
. Historically the term was used to describe materials composed of amphiphilic molecules. Such molecules comprise a water-loving 'hydrophilic' head-group (which may be ionic or non-ionic) attached to a water-hating 'hydrophobic' group. Typical hydrophobic groups are saturated or unsaturated hydrocarbon chains. Examples of amphiphilic compounds are the salts of fatty acids; phospholipids. Many simple amphiphiles are used as detergents. Lyotropic liquid crystal
Lyotropic liquid crystal
A liquid crystalline material is called lyotropic if phases having long-ranged orientational order are induced by the addition of a solvent. Historically the term was used to describe materials composed of amphiphilic molecules. Such molecules comprise a water-loving 'hydrophilic' head-group ...
phases in these materials are formed by a process of self-assembly that is driven by the hydrophobic effect
Hydrophobic effect
The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules. The name, literally meaning "water-fearing," describes the segregation and apparent repulsion between water and nonpolar substances...
.
Lyotropic liquid crystal phases are formed on the dissolution of amphiphilic molecules of a material in a solvent. There are several different type of lyotropic liquid crystal structures. Each of these different types has a different extent of molecular ordering within the solvent matrix.
The term lyotropic has also been applied to the liquid crystalline phases that are formed by certain polymeric materials, particularly those consisting of rigid rod-like macromolecules, when they are mixed with appropriate solvents. Examples are suspensions
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...
of rod-like virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es as the Tobacco Mosaic Virus
Tobacco mosaic virus
Tobacco mosaic virus is a positive-sense single stranded RNA virus that infects plants, especially tobacco and other members of the family Solanaceae. The infection causes characteristic patterns on the leaves . TMV was the first virus to be discovered...
as well as man-made colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
al suspensions of non-spherical colloidal particles. Other examples include DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
, which dissolves in sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
to give a lyotropic phase. It is noted that in these cases the solvent acts to lower the melting point of the materials thereby enabling the liquid crystalline phases to be accessible. These liquid crystalline phases are closer in architecture to thermotropic
Thermotropic
A liquid crystal is thermotropic if the order of its components is determined or changed by temperature.If temperature is too high, the rise in energy and therefore in motion of the components will induce a phase change: the LC will become an isotropic liquid.If, on the contrary, temperature is...
liquid crystalline phases than to the conventional lyotropic phases. In contrast to the behaviour of amphiphilic molecules, the lyotropic behaviour of the rod-like molecules does not involve self-assembly.