Classification of Liquid Crystals

The liquid crystalline phase exists between the state of a crystalline solid and that of the isotropic liquid. The LC-phase (liquid crystal) is also called mesophase (Greek: mésos = center), and the molecules that can form such mesophases are called mesogens.

The LC phases are classified as follows:

Thermotropic mesophases are formed on heating a solid and / or cooling an isotropic liquid. These thermotropic phases are further subdivided into enantiotropic mesophases (observable in the heating and cooling process, thermodynamically stable within a certain temperature range) and monotropic mesophases (observable when an isotropic liquid or an enantiotropic mesophase is metastable).

Lyotropic mesophases are obtained by dissolving an amphiphilic mesogen in a suitable solvent.

"Definitionen von Grundbegriffen mit Bezug zu niedermolekularen und polymeren Flüssigkristallen", Carsten Tschierske, Gerhard Pelzl, Siegmar Diele, Angew. Chem. 2004, 116, 6340 –6368.