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. Further, biological structures such as the lipid bilayers of cell membranes are examples of mesophases.

Georges Friedel (1922) called attention to the "mesomorphic states of matter" in his scientific assessment of observations of the so-called liquid crystals. Everyone knows a crystal is solid and to crystallize is to make solid. The oxymoron of the liquid crystal is resolved through the notion of mesophases. The observations noted an optic axis persisting in materials that had been melted and had begun to flow. But the catch-phrase of the liquid crystal caught on, even when displaced in technical writing.

For example, in The Physics of Liquid Crystals the mesophases are introduced from the beginning:

Further, "The classification of mesophases (first clearly set out by G. Friedel in 1922) is essentially based on symmetry."

Molecules that demonstrate mesophases are called mesogens.

In technology, molecules in which the optic axis is subject to manipulation during a mesophase have become commercial products as they can be used to manufacture display devices. The susceptibility of the optic axis, called a director, to an electric or magnetic field produces the potential for an optical switch. Methods used include the Freedericksz transition and the twisted nematic field effect. From early liquid crystal displays the buying public has embraced the low-power optical switch facility of mesophases with director.

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