DIRECT VISUALIZATION OF MONOLAYERS AT THE AIR-WATER-INTERFACE BY BREWSTER-ANGLE MICROSCOPY

No light is reflected from the air-water interface under Brewster angle incidence if p-polarized light is used. With constant angle of incidence, the formation of a monolayer on the water surface modifies the Brewster angle condition, and light reflection is observed. Reflectivity-area isotherms of arachidic acid monolayers on pure water and on aqueous solutions of different pH have been measured. Areas of different brightness due to different molecular density and/or refractive index in the monolayer have been recorded with a video system as micrographic pictures. This Brewster angle microscopy enables us also to detect monolayer inhomogeneities and the reversible formation of solid-phase domains upon compression of monolayers of DMPE.