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Structure and Properties of Lyotropic Liquid Crystals |  |
Liquid crystals come in two basic classifications: thermotropic and lyotropic . The phase transitions of thermotropic liquid crystals depend on temperature, while those of lyotropic liquid crystals depend on both temperature and concentration. This section will focus on lyotropic liquid crystals.
Lyotropic liquid crystals were actually discovered long before their thermotropic counterparts were known. In 1850, their texture was noticed in a mixture of myelin and water. At the time of discovery, however, the significance of liquid crystals was not understood, so most research has been done on thermotropics. Only fairly recently have lyotropic liquid crystals begun to catch up.
The molecules that make up lyotropic liquid crystals are surfactants consisting of two distinct parts: a polar, often ionic, head and a nonpolar, often hydrocarbon tail. (Not all surfactants, however, form lyotropic liquid crystals.) Following the rule of "like dissolves like," the head is attracted to water, or hydrophilic, and the tail is repelled by water, or hydrophobic. When dissolved in high enough concentrations, the molecules arrange themselves so that the polar heads are in contact with a polar solvent and/or the nonpolar tails are in contact with a nonpolar solvent.
Lyotropic liquid crystals are found in countless everyday situations. Soaps and detergents form lyotropic liquid crystals when they combine with water. In the kitchen, cake batters may harbor the liquid crystals as well. Most importantly, biological membranes display lyotropic liquid crystalline behavior.
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Structure and Properties of Lyotropic Liquid Crystals | |