The diffuse scattering of x rays by the thermally excited out-of-plane fluctuations of different amphiphilic films was measured for in-plane wavelengths down to the nanometer range, giving access to nontrivial bending effects. The Helfrich Hamiltonian applies on pure water and in the solid phase of an arachidic acid monolayer a large bending rigidity constant was measured. When formed on a subphase containing divalent cadmium ions, the height-height fluctuation spectrum ⟨z(q)z(−q)⟩ is greatly modified: no longer consistent with a q−4 law at large wavelengths but rather with a q−3.3±0.2 law, revealing a very different physical mechanism whose origin is discussed.

The growth and entanglement of cetyltrimethylammonium tosylate (CTAT) micelles with and without added salt are investigated using the fluorescence recovery after fringe pattern photobleaching (FRAPP) technique. In the absence of salt the micelles grow slowly in the concentration range 0.06−0.7 wt % and get entangled beyond an overlap concentration of 0.7 wt %. With added salt of 0.1 and 1 M KBr, the slow growth is not observed and the entanglement seems to exist right from the lowest concentration used in this study (0.07 wt %). The variation of self diffusion coefficient with concentration in the presence of salt is found to be in accordance with the recent theoretical predictions for the scaling of the diffusion constant with concentration. The modes of micellar diffusion are discussed under the purview of these scaling laws.

We have studied the “collective” diffusion of a concentrated solution of “living polymers” in brine, which in certain concentration conditions exhibit superdiffusive (Lévy flight) behaviour when tracer diffusion is considered. The concentration profile of the diffusion front is monitored over time using a Michelson interferometer. We show how a concentration dependent diffusion constant can be extracted from the fringe pattern. We find that the diffusion constant decreases linearly with increasing concentration, at variance with a power-law dependence, expected when the interaction between chains is neglected.

In order to explore the compressibility of water sequestered in droplets surrounded by surfactant molecular films (reverse micelles), we custom-built a high-precision velocimeter. The apparatus comprises two ultrasonic small-sized cells, electronic generators and a computer-controlled digital scope. We carried out a systematic study of the stability and reproducibility of the experimental set-up which yields an accuracy of 10^-5. The ultrasound velocity, the apparent volume, and compressibility of encapsulated water were determined in charged and uncharged molecular films as a function of water concentration. We observed a close relationship between the measured parameters of encapsulated water, the chemical nature of the surfactant molecular film and the number of water molecules in interaction. The values obtained are higher than that reported for bulk water and are assigned to the surfactant-water interactions arising between the head groups and water molecules.

We have performed small angle x-ray scattering experiments on a ternary system made of a nonionic surfactant, dodecane, and water, in the absence and upon insertion of a transmembrane protein. In contrast to other proteins or polymers studied, its incorporation reduces the Bragg spacing from 200 Å to 80 Å, which scales as c−0.5, where c is the protein surface density. The macromolecule incorporated into the hydrophobic part of the lamellar phase appears on freeze-fracture electron micrographs as intramembranous particles. The data are fitted by a simple model of thermally undulating lamellae decorated with protein molecules.