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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 (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.
== Amphiphile self-assembly ==
Amphiphilic molecules form aggregates through a self-assembly process that is driven by the 'hydrophobic effect' when they are mixed with a solvent, which is usually water. The aggregates formed by amphiphilic molecules are characterised by structures in which the hydrophilic head-groups shield the hydrophobic chains from contact with water. For most lyotropic systems aggregation occurs only when the concentration of the amphiphile exceeds a critical concentration (known variously as the 'critical micelle concentration' (CMC) or the 'critical aggregation concentration (CAC)'). Micellar solutions are often denoted by the symbol L1.
Above the CMC the self-assembled amphiphile aggregates exist as independent entities, in equilibrium with monomeric amphiphiles in solution, and with no long ranged orientational or positional (translational) order. These dispersions are generally referred to as 'micellar solutions', the constituent aggregates being known as 'micelles', and are 'isotropic' phases (i.e. not liquid crystalline). True lyotropic liquid crystalline phases are formed as the concentration of amphiphile in water is increased beyond the point where the micellar aggregates are forced to be disposed regularly in space. For amphiphiles that consist of a single hydrocarbon chain the concentration at which the first liquid crystalline phases are formed is typically in the range 25-30 wt%.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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