No abstract

We show, using surface pressure versus molecular area isotherms measurements and x-ray reflectivity, that the long diblock semifluorinated n-hexaeicosane molecules, F(CF2)(8)-(CH2)18H, form a stable smectic bilayer phase, noted M1, with a total thickness of 3. 3 nm, at an apparent molecular area about 0.3 nm(2), though in the bulk the used molecules do not form smectic phases at any temperature. We discuss different molecular packing models according to our experimental data and deduce that molecules are antiparallel with fluorinated chains outwards and interleaved hydrocarbon chains inwards.

Studies of the structure of microemulsions and of Winsor-type systems have emphasized the importance of the properties of the interfacial film through the parameters of spontaneous curvature and film curvature elastic modulus. Surface light scattering and ellipsometric studies have been carried out on the interfacial film between two macroscopic phases in a variety of surfactant systems. Measurements of rigidity allow us to calculate the persistence length of the monolayer, which is in qualitative agreement with the one required to explain the bulk structure observed. A comparison with theoretical calculations of the low tensions is also presented.

We show the spontaneous formation of an antiparallel monolayer of diblock semifluorinated n-alkane molecules spread at the air-water interface. We used simultaneous measurements of surface pressure and surface potential versus molecular area and performed grazing x-ray reflectivity experiments to characterize the studied monolayer, which is obtained at almost zero surface pressure and precedes the formation of a bilayer at higher surface pressure. Its thickness, equal to 2.7 nm, was found to be independent of the molecular area. This behavior may be explained by van der Waals and electrostatic interactions.