Insoluble monolayers of the trifluoroethyl ester of behenic acid possessing a terminal CF3 group of the ester radical of the hydrophilic head are studied at the air-water interface. The surface pressure-area isotherms show a formation of condensed monolayer. The relatively low collapse pressure and significant reduction with time of the molecular area at constant surface pressure illustrate considerable decrease of the monolayer stability when compared to the one of the ethyl behenate monolayers. The CF3 terminal of the ester radical reverses the sign of the surface potential and the vertical dipole moment component; negative values of Delta V and mu(perpendicular to) are obtained for the trifluoroethyl behenate monolayer, while positive values of Delta V and

Keywords:AIR-WATER-INTERFACE;SURFACTANT MONOLAYERS;LIPID MONOLAYERS;DIPOLE-MOMENTS;4-HEPTADECYL-7-HYDROXYCOUMARIN;FORCES