OPTICAL MEASUREMENTS OF AN ACYLATED AZACROWN AT THE AIR-WATER-INTERFACE

In this study, a cyclame derivative bearing four aliphatic chain substituents shows, like many amphiphiles, solid-condensed as well as liquid-expanded phases. In contrast to the classical amphiphiles, the onset of its phase transition is characterized by a bump-like shape whose amplitude is a function of the compression speed. Ellipsometry which is very sensitive to the monolayer physical state changes, and fluorescence microscopy which has contributed significantly to the understanding of the phenomena occurring in the phase transition region have been used to investigate the monolayer behavior of this compound. This study shows that in the liquid-expanded state, the film is homogeneous and remains as such until either the maximum amplitude of the bump is reached or the beginning of the plateau sets in. Thereafter, heterogeneity with formation of diamond-like domains appears with domain sizes varying with compression speed. The formation of the domains coincides with a change in the ellipsometric zone differences. From this ellipsometric behavior, a change in the distribution of the orientation of the molecules is suggested to take place at the onset of the phase transition.