SOME REMARKS ON THE EVOLUTION OF RESEARCH INTO THE STRUCTURES OF MESOGENS AND MESOPHASES

Research on mesogens and mesophases began with the surprising observat ion of a fluid and birefringent phase formed by a pure compound having a calamitic (rod-like) molecule. The structures of the smectic A, nem atic and cholesteric phases which emerged after this discovery were el ucidated essentially by observations with a polarizing microscope. Sme ctic polymorphism was also established by microscopic observations. Th e main historical results on the structures of the different smectic m esophases are listed here. The discotic mesophase, previously predicte d theoretically, was then obtained and its polymorphism observed. A fu rther type of purposely designed mesophase was the pyramidic type, als o exhibiting a rich polymorphism. Research on mesogens and mesophases is a field in continuous expansion.