Surface crystallization and phase transitions of the adsorbed film of F(CF 2 ) 12 (CH 2 ) 16 H at the surface of liquid tetradecane

Experimental validation of the Helmoltz equation for the surface potential of Langmuir monolayers

We show in this paper that monolayers of the nonhydrophilic F8H18 semifluorinated n -alkane constitute when spread on the hydrophobic top of an alamethicin Langmuir monolayer, a very good experimental system in order to check the validity of Helmoltz equation. This system allows for a good agreement between measured and calculated surface potentials of unionized Langmuir monolayers. We show also that the relative dielectric constant of the F8H18 monolayer does not vary upon compression of the monolayer, the measured 2.9 value is in a very good agreement with literature data. We attribute this behavior to the self-aggregation of F8H18 molecules in nanosized circular domains whose size remains constant upon compression as shown by atomic force microscopy.

Semifluorinated alkanes--primitive surfactants of fascinating properties

Semifluorinated alkanes (SFAs) are diblock molecules, in which two mutually immiscible moieties, namely the hydrocarbon segment and the perfluorinated segment are bound covalently. The presence of two opposing segments within one molecule makes semifluorinated alkanes a very interesting class of compounds, which show a particular behavior both in bulk and at interfaces. Their highly asymmetric structure, arising from the incompatibility of the both constituent parts, results in surface activity of these molecules (so-called primitive surfactants) when dissolved in organic solvents, and allows for the Langmuir monolayer formation if spread at the air/water interface, despite of the absence of any polar group. Since 1984 (when SFAs have been characterized for the first time by Rabolt et al. [Rabolt JF, Russell TP, Twieg RJ. Macromolecules 1984;17:2786]), semifluorinated alkanes have been subjected to many studies. The present article reviews the results obtained so far and covers the aspects of their synthesis, properties in bulk (solutions and solid state) and applications. Special emphasis is put on the Langmuir monolayer properties and self-organization of SFAs on solid substrates.

Structural and electric properties of two semifluorinated alkane monolayers compressed on top of a controlled hydrophobic monolayer substrate

We investigate the dynamic behavior upon lateral compression of two mixed films made with one of the two semifluorinated alkanes F(CF2)8(CH2)18H and F(CF2)10(CH2)10H and the natural alpha-helix alamethicin peptide. Surface pressure, surface potential versus molecular area isotherms, and grazing-incidence x-ray diffraction were applied to characterize this system. We show that both mixed films demix vertically to form two asymmetric flat bilayers where the lower layer is made of alamethicin and the upper layer is made of semifluorinated molecules. The structure matching of the semifluorinated alkanes (where the hydrophilic group is missing) with a suitable organization of the underlying alamethicin monolayer allows for a continuous compression of the upper semifluorinated layers while the density of the lower alamethicin monolayer remains constant. Comparing data of the two studied mixed films enables us to evaluate the effect of chain length on the in-plane organization of the molecules and on the electric properties of the upper layers.

Assembling and compressing a semifluorinated alkane monolayer on a hydrophobic surface: structural and dielectric properties

We investigate the dynamic behavior upon lateral compression of a semifluorinated alkane F (CF2)8(CH2)18H (denoted F8H18), spread on the hydrophobic top of a suitable amphiphilic monolayer: namely, a natural alpha-helix alamethicin peptide (alam). We show, in particular, the formation of an asymmetric flat bilayer by compressing at the air-water interface a mixed Langmuir film made of F8H18 and alam. The particular chemical structure of F8H18 , the suitable structure of the underlying alam monolayer and its collapse properties, allow for a continuous compression of the upper F8H18 monolayer while the density of the lower alam monolayer remains constant. Combining grazing incidence x-ray reflectivity, surface potential, and atomic force microscopy data allow for the determination of the orientation and dielectric constant of the upper F8H18 monolayer.