ON THE STABILITY OF LANGMUIR FILMS OF PYRAMIDIC MESOGENS

Pyramidic mesogens forming thermotropic liquid crystal bulk phases wer e spread in an air-water interface. Pressure surface measurements and polarizing microscopy on the Langmuir films were used to characterize the various states of these pyramidic-like molecules. For two compound s bearing short lateral aliphatic chains, the surface pressure isother ms exhibit a large plateau region corresponding to a metastable monola yer in which the molecules may adopt an 'edge-on' arrangement. The coe xistence of multilayered, anisotropic, slowly growing domains with the monolayer in the plateau region has been observed at long time scale. The film area relaxation kinetics at constant surface pressure show t he existence of two nucleation mechanisms for the formation of these d omains.