We have determined the boundaries of the single-phase water-in-oil microemulsion region of a ternary system (tetraethylene glycol monododecyl ether−dodecane−water) in the oil-rich corner of the phase diagram, as a function of water content and temperature. We have investigated the structures of reverse micelles at temperatures between the lamellar (LC) phase transition and the two-phase separation. Characterization studies have been carried out by dynamic quasi-elastic light scattering and small-angle X-ray scattering as well as by viscosity measurements. It was found that a consistent interpretation of the experimental results requires the complementarity of the above techniques. At a constant water-to-surfactant molar ratio of 13.7, the emerging picture of the isotropic phase is that near the two-phase boundary, micelles behave as slightly solvated spheres of 52-Å radius. With decreasing temperature and as the LC transition is approached, prolate aggregates, displaying an asymmetry of 6 ± 2 are formed and can be considered to be a progressive structural change on the way to lamellae. The physical properties of the system reported herein may have implications for the investigation of proteins in membrane-mimetic media.

The swelling behavior of an L3 (sponge) surfactant phase was studied by the small angle x-ray scattering technique; we show that it is well described by the recently computed swelling law for minimal surfaces. In addition, the self-diffusion coefficient DS of several probes within the bilayers of the L3 phase was measured by the fluorescent recovery after fringe pattern photobleaching technique. The variation of DS with the surfactant volume fraction provides a clue for the topology of the surface over which the midsurface of the bilayers is draped. This allows us to determine the location of the neutral surface near the polar-apolar interface of the bilayers.

Molecular recognition occurs at all levels of living matter but the mechanisms are not understood in physical terms. One striking example is that of DNA whose properties are intimately related to the specific molecular interactions of four nucleosides, based on hydrogen-bonds and size complementarities. We have directly measured the interaction between two of them, adenosine and thymidine, using a surface force apparatus. In these experiments, lipids functionalised with nucleosides were synthesised, and used to coat the surfaces between which forces were measured. The interactions of complementary molecules were compared to those, markedly different, for which the complementarity was hindered by a small modification of one of the molecules. The distance range of the specific forces, deduced from this comparison, was surprisingly long. The adhesion energy of the surfaces covered by these nucleosides were highly specific. Binding energies obtained from these measurements were in good agreement with values from the literature. The results also show that without tile size effect existing in DNA, H-bonds alone can generate the specificity. An unusual behaviour, attributed to the sticky and fluid character of the layers, was pointed out. A long-range non specific interaction, also unexpected, was found. These features observed on surfaces coated with chemical functional groups may partly result from a collective behaviour. They illustrate the variety of physical effects one can obtain by playing oil the chemistry of a surface.

A comprehensive presentation of new developments in the theory of diffuse (off-specular) surface scattering of X-rays is given and illustrated with experimental results on different kinds of films and surfaces. This technique allows the determination of surface and interface morphology through height–height correlation spectra over a wide in-plane wave-vector range (10⁵–10¹⁰ m^–1). A general method for the determination of the tensorial Green function relevant to the problem is indicated. The Born approximation and the more accurate distorted-wave Born approximation are evaluated. The need for even better approximations is stated and possible methods are indicated. The theoretical results are compared with the results of experiments and non-trivial effects are evidenced. Finally, different methods for the measurements of liquid fluctuation spectra with synchrotron radiation are discussed, demonstrating the ability of this technique to provide more insight into the statistical physics of liquid interfaces down to molecular scales.

We report on small-angle x-ray scattering and free-fracture electron microscopy studies of a nonionic surfactant/water/polyelectrolyte system in the lamellar phase region. The surface tension data show that the polymer-surfactant interaction strongly depends on the polymer charge content. We demonstrate that regardless of the charge content the polymer molecules are confined inside the bilayers. The chains are collapsed into individual coils which are randomly spread in the bilayers. The polymer molecules cause both local deformation and softening of the bilayer.