Michel Goldmann

Molecular packing in water supported monolayers of F(CF2)11COOH and F(CF2)10CH2COOH

We report the results of a grazing incidence x‐ray diffraction study of monolayers of F(CF2)11COOH and F(CF2)10CH2COOH on water at several temperatures. It is found that in both monolayers the amphiphile molecules have a very small collective tilt angle (relative to the normal to the surface). For the temperature range studied (∼4–30u2009°C) the data for both monolayers indicate the existence of only a first‐order transition between an ordered condensed phase and a disordered dilute phase; there is no evidence, in this temperature range, for the existence of a continuous tilt transition such as has been observed in monolayers of arachidic acid. The experimental data suggest that the critical point for the transition observed is at a lower temperature for a monolayer of F(CF2)11COOH than for a monolayer of F(CF2)10CH2COOH.

Structure of Smectic Defect Cores: X-Ray Study of 8CB Liquid Crystal Ultrathin Films

We study the structure of very thin liquid crystal films frustrated by antagonistic anchorings in the smectic phase. In a cylindrical geometry, the structure is dominated by the defects for film thicknesses smaller than 150 nm and the detailed topology of the defects cores can be revealed by x-ray diffraction. They appear to be split in half tube-shaped rotating grain boundaries (RGB). We determine the RGB spatial extension and evaluate its energy per unit length. Both are significantly larger than the ones usually proposed in the literature.

Hysteresis of the metal-insulator transition of ; evidence of the influence of microscopic texturation

Vanadium dioxide films have been deposited on silicon substrates by reactive RF cathodic sputtering from and targets. The optical measurements show a good contrast at the semiconductor-metal transition, but exhibit two kinds of hysteresis cycle: a narrow and symmetrical one, and a wider and asymmetrical one. We have mainly studied the microstructure of these samples by means of grazing-incidence x-ray diffraction at the LURE synchrotron radiation facility. We analysed in detail the intensities of the diffraction peak spectra and of the portions of diffraction rings. We found a clear relation between a narrow and symmetrical hysteresis cycle, and a (011) texture of the films. We attribute this result to an improvement in the cooperativity of the transition phenomena.

Interaction of dipyridamole with phospholipid monolayers at the air–water interface: Surface pressure and grazing incidence X-ray diffraction studies

Incorporation of dipyridamole (DIP) in Langmuir monolayers of the zwitterionic phospholipid dipalmitoylphosphatidylcholine (DPPC) has been investigated using surface pressure isotherm and grazing incidence X-ray diffraction (GIXD) measurements. An expansion in the pressure–area isotherms of the DPPC monolayer was observed, which was maximum in the liquid-expanded (LE) to liquid-condensed (LC) transition region and at a DIP concentration of 2 mol%. Accordingly, the GIXD measurements indicated an expansion of the 2D lattice in the LC phase up to a surface pressure of ca. 30 mN/m. A condensation effect on the DPPC packing for high DIP concentrations, as previously suggested, can be ruled out.

Search for perfectly ordered dense monolayers

We present some basic criteria to obtain well-ordered Langmuir monolayers and of high surface densities. The fluorinated molecules such as C10F21CH2COOH and C11F23COOH appear as good candidates to fulfill these requirements. Independent, grazing incidence X-ray diffraction and surface pressure isotherm measurements give an advantage to the first molecule. This may have some important practical applications in the surface modification of solid substrates (e.g. silicon wafers) by thin organic layers. Assuming that a water film is present on the solid substrate prior to deposition, the above comments on Langmuir monolayers strongly suggest that fluorinated silanes should form optimum grafted monolayers.

Structure of bidimensional phospholipidic crystallites on formamide determined by X-ray diffraction

Abstract By using grazing incidence X-ray diffraction, we determined the structure of the solid phase of a C18ue5f8C18 phosphocholine monolayer spread at the air-formamide interface. The chains are organized on an oblique lattice, and their tilt, measured from Bragg rod scans, is about 35°. No structural change is observed when the surface pressure is varied from 1 to 38 mN/m. In the solid phase, the area per molecule is 46 A2, and the compression modulus is large. The phase stiffness is dominated by the interactions between the polar heads and the formamide, more than between the aliphatic chains.