About Liquid Crystals
The Liquid-crystalline State - Molecular Shape and Structure and Liquid Crystals - Thermotropic Liquid Crystals - Lyotropic Liquid Crystals - Plastic Crystals - Structures of Thermotropic Liquid Crystals - Structures of Smectic Liquid Crystals
Lyotropic Liquid Crystals
Liquid-crystalline mesophases can also be formed in mixtures of amphiphiles (eg, surfactants and solvents, such as detergents and water). Here the phases are thermodynamically stable at defined temperatures, pressures, and concentrations. A variety of structurally distinct modifications exist. Collectively, these phases are known as lyotropic liquid crystals.
The molecular structure of a typical amphiphile is one where a hydrophilic polar head group is appended to a hydrophobic aliphatic moiety.
When a lyotropic mesogen dissolves in a solvent it can form one or more of a number of phases depending on the size of the polar head group, the number of aliphatic chains present in the amphiphile, and the nature (polarity) of the solvent. The phases formed are dependent on the concentration of solvent and the degree of curvature produced by the packing arrangements of the amphiphilic molecules. For example, in the low curvature lamellar phase the constituent molecules are arranged in layers which are separated by molecules of the solvent. Increased curvature produces a hexagonal phase where the surfactant molecules form columnar structures which can pack in hexagonal arrays, and further increasing the curvature results in the formation of micelles.
Typically, when solvated in a polar solvent, the polar part of the amphiphile will interact strongly with the solvent to give a normal micellar structure. However, in a non-polar solvent the non-polar regions of the amphiphile will interact more strongly with the solvent causing the polar groups to aggregate. In this situation reversed micellar structures are formed. Although not used in optical or electronic devices, these phases are commonly found in soap/water and detergent/water systems. An understanding of the rheological properties of lyosystems is of a fundamental importance to industry.
The Liquid-crystalline State - Molecular Shape and Structure and Liquid Crystals - Thermotropic Liquid Crystals - Lyotropic Liquid Crystals - Plastic Crystals - Structures of Thermotropic Liquid Crystals - Structures of Smectic Liquid Crystals