COLUMNAR PHASES OF PYRAMIDIC AMPHIPHILES SPREAD AT THE AIR-WATER-INTERFACE

Two compounds, forming thermotropic liquid-crystalline phases in the b ulk, were spread at the air-water interface. For both compounds, the s urface pressure versus molecular area diagrams exhibit a large domain of molecular areas where the surface pressure of the film is quasicons tant. This plateau region of the isotherms corresponds to a transition from a monolayer in a liquid-expanded phase to a metastable condensed monolayer in which the molecules may adopt an << edge-on >> arrangeme nt. In this arrangement, the base of the pyramidic core is normal to t he air-water interface. The film was also observed by means of fluores cence and polarizing microscopy. These techniques allowed us to show t he formation of anisotropic slowly growing multilayered domains from t he << edge-on >> monolayer. An original method, based on the light ref lectivity of the domains, was developed to measure their thickness and their optical anisotropy. The results show that these domains are for med by an arrangement of the molecules in rectilinear columns for one compound and in spiral columns for the other compound.