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A study was conducted to analyze dilute solutions of the ganglioside GM3 in water using small-angle neutron and x-ray scattering techniques. The ganglioside was prepared as sodium salt. Two different wavelengths were utilized to carry out experiments of small-angle neutron scattering. In addition, the Huxley-Holmes camera was used to perform small-angle x-ray scattering. Results indicated thickness fluctuations originating from the mismatch between headgroup and chains lateral hindrances.

The issue of the origin of the bending rigidity of a charged membrane formed from amphiphilic molecules is addressed. Electrostatic effects are investigated by direct measurement of the force that is required for deforming a catanionic membrane as function of the ionic strength of the medium by means of an atomic force microscope.

Measures the entropy of the lamellar-lamellar transition in the surfactant, didodecyldimethylammonium bromide. Application of osmotic stress and varying temperature; Consideration of lateral compressibility in the free energy balance; Release of the degrees of freedom associated with the bilayer condensation.

Studies on third phase formation during the extraction of nitric acid by malonamide extractants in various diluents are investigated. This "third phase transition" is studied from a fundamental point of view, combining vapor pressure osmometry, phase diagram, and scattering studies. The organization of the organic phases of the "malonamides/alkane/water/nitric acid" systems was studied at three "scales": 1/at a molecular scale by determining the compositions of the extracted complexes; 2/at a macroscopic scale by determining the phase transition boundaries quantified by the limiting organic concentration (LOC) of solutes; and 3/at a supramolecular scale by analyzing the organization of the species in the organic phases (i.e. measuring the critical micellization concentration, the aggregation number, and the interactions between the aggregates). The instability (third phase apparition) has a supramolecular origin: it is a "long range" attraction between polar cores of the reverse micelles formed by the extracting agent. Water and nitric acid extraction are decoupled from these interactions. The alkyl chains of the extractant and the diluent play a symmetrical role in the physical stability of the organic phase: decreasing the diluent chain length or increasing the chain length of the complexing agent both promotes phase stability, i.e. they increase the LOC. We demonstrate here that this effect is the same as the effect observed and known for all other w/o "reverse" micelles: chains protruding from any aggregate stabilize polar solute in oil and shorts oil penetrate and swells the reverse micelles apolar layer. [ABSTRACT FROM AUTHOR]

We show that a significant improvement in the sensitivity of a Huxley-Holmes design for a small angle x-ray scattering camera is obtained by separating the mirror and the monochromator. The design of the camera involves a long x-ray mirror close to a point x-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard x rays allows precise calibration and hence absolute determination of sample cross section by means of a semitransparent beam stop. In pinhole geometry, the flux corresponds to a ∼10[SUP7] photons/s through the sample, collimated to 10[SUP-2] Å[SUP-1] in q range. This allows determination of scattered intensities on the order of 10[SUP-3] cm[SUP-1], corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. As a reference sample, the widely used Lupolen™, a semicrystalline polymer, is calibrated. The high-q limit (q≈4.5 nm[SUP-1]) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid-liquid dispersions. [ABSTRACT FROM AUTHOR]

The behaviour of a di-block molecule associating a diamide group and a non-ionic surfactant (C(i)E(j)) is determined in a ternary surfactant/water/oil/system. Its properties are compared to the ones of a parent non-ionic surfactant C(i)E(j) through the limits of boundaries in the phase prisms. The existence of a stable microemulsion single phase in a defined temperature and concentration range is demonstrated. The extension of the microemulsion domain is limited by the presence of a gel, containing lyotropic liquid crystals as gelling agents. Temperature dependence is observed for the curvature below the temperature of zero spontaneous curvature, but the ternary system cannot produce reverse microemulsion as observed with classical C(i)E(j). The decrease of the mean curvature with temperature is inhibited by the presence of the diamide as a grafted complexing group. Liquid-liquid extraction processes with this type of surfactant are possible, but will require the presence of at least a fourth component to enlarge the water in an oil microemulsion domain.

In the present paper, it is shown that in malonamide extractant/dodecane mixtures, change in the shape of the extractant aggregate may promote phase demixion. This phenomenon is known as the 3rd phase formation in extractant systems. The shape of the aggregates is dictated by the length of the alkyl chains stabilizing the reverse microemulsion by steric repulsion. Small angle scattering experiments are used to investigate the aggregation states of diamide extractant molecules, namely N,N'dimethyl-N,N'dibutyl-tetradecyl malonamide (DMDBTDMA) and N,N'dimethyl-N,N'dibutyl-pentyl malonamide (DMDBPMA), in dodecane. The results are described in a consistent way by the packing parameter concept and by expressing steric repulsion versus Van der Waals inter-aggregate interactions, both curvature dependants. Non-monotonous change in the extractant Critical Micellar Concentration (CMC) as a function of the extractant alkyl chain length is rationalized by comparing Van der Waals attraction between the alkyl chains of both the extractant and the solvent.