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We show that it is possible to measure the porosity of facetted micron-sized hollow icosahedra of catanionic solutions by performing fluorescence recovery after photobleaching measurements. The size of spontaneous permanent pores in bilayers formed via molecular segregation is compatible with what is observed by freeze-fracture electron microscopy and is discussed versus theoretical expressions of bending energy.

New functional thermoreversible metal complexing surfactants consisting of a chelating amino acid residue grafted to the tip of a nonionic surfactant [alkyl poly(oxyethylene) CiEj] or in a branched position are studied. Nonionic surfactants are thermoreversible and exhibit a clouding phenomenon associated with phase separation of micelles. The functional molecules retain both the surface-active properties and the characteristic thermoreversible behavior. Because of the hydrophilic contribution of the chelating group (acetyl lysine), the cloud point and the area at the air−water interface are higher for functional surfactants than for nonionic precursors. These new surfactants have efficient complexing properties toward metal ions and are more efficient than the mixture of the corresponding nonionic surfactant and the acetyl lysine ligand solubilized in micelles. This reveals the synergistic effect obtained by the covalent link between the two functions. Addition of a bulky group on classical amphiphilic structures modifies markedly the packing constraints at the origin of micellar structures. Small-angle X-ray or neutron scattering results, modeled jointly on the absolute scale, demonstrate the influence of unrecognized lithium nitrate (LiNO3) as well as specifically recognized uranyl nitrate [UO2(NO3)2] salts on micellar structure and phase boundaries. The determination of the micellar shape variations induced by a recognized salt, that is, a decrease of the polar headgroup, allows the rationalization of uncommon synergistic effects on the cloud point variation: increase with lithium nitrate, no decrease in the presence of uranyl nitrate, and a very large decrease when these two salts are present together.

The investigation of the dilute range in the system of myristic acid, cetyltrimethylammonium hydroxide, and water shows that the formation of charged catanionic microcrystallites induces measurable osmotic pressures. In the coexistence region between the lamellar phase and the disk phase, we observe a slight osmotic pressure drop, which is due to the crossing of tie lines during dilution. With the application of the Poisson−Boltzmann theory, the surface charge densities of icosahedral and disklike particles are estimated to determine the equation of state of these self-assembled aggregates in the dilute regime. In typical conditions, a hollow crystallite of 1-μm diameter has an effective charge on the order of 1.8 × 10⁶, while the structural charge is 1 order of magnitude larger.

The equation of state of a charged phospholipid (dioleoylphosphatidylserine:  DOPS, Na⁺) in the absence of added salt is given at room temperature over six decades of osmotic pressure (100 to 2 × 10⁸ Pa) covering the range of pressures where the different structures described previously have been observed.¹ It is compared to the universal expression given by the Langmuir equation and predictions for the Gouy−Chapman regime for highly charged bilayers. Below membrane separations of 10 Å, the pressure of solid supported DOPS films is higher than the prediction of the Langmuir equation. In the linear swelling regime of flat bilayers and up to the regime where giant correlated fluctuations are present (the oyster shell state), the Langmuir equation holds better than the prediction given by Attard et al.² for the Gouy−Chapman regime. Close to maximum swelling (700 Å), the pressure drops sharply. However, the universal power-law decay still holds in the unbinding regime, where the oyster shell state coexists with vesicles. The unbinding occurs as a progressive transformation of the oyster shell state into closed vesicles by a peeling mechanism of the lamellar domains.

We show the existence of a new and unexpected morphology of charged phospholipid membranes composed of pure dioleoylphosphatidylserine (DOPS, Na⁺) in the absence of added salt. This new morphology is characterized by giant collective fluctuations of locally lamellar stacks of membranes at the lamellar-to-vesicle unbinding transition. The DOPS dispersions have been studied in pure water and at rest using complementary techniques:  small-angle scattering (neutron and X-ray) and freeze-fracture electron microscopy. In the present case of strong unscreened electrostatic interaction, we show that the order-to-disorder transition associated with the lamellar phase unbinding into vesicles is hidden by the presence of this intermediate state of strongly coupled undulating membranes where electrostatic and entropic forces compete. The giant collective fluctuations produce a texture analogous to that of an oyster shell as observed by freeze-fracture electron microscopy. Three microstructures are encountered along the dilution line of bulk samples:  an Lα lamellar phase with linear swelling, the lamellar oyster shell state characterized by giant collective fluctuations, and finally stable single- or multilayer vesicles formed spontaneously by a peeling mechanism of the fluctuating membranes as suggested by the period of the undulations close to the size of the vesicles.

The grafting of a cholesterol derivative onto a methylated cyclodextrin through a spacer arm produces an amphiphilic compound exhibiting high solubility in water. This new molecule was fully characterized in terms of chemical and optical purities by high resolution NMR and mass spectrometry. An analysis of its behavior in aqueous solution using surface tension measurements and light, small-angle X-ray, and neutron scattering techniques proved that it self-assembles into monodisperse spherical micelles with an average aggregation number of 24. The micelles can be described as two-shell objects, the cyclodextrin moieties being exposed to the aqueous medium, making them prone to include guest molecules in the cavities. These objects can therefore be of high interest for the targeting of biologically important molecules and especially for the delivery of drugs.

A gradient method to determine directly and quantitatively ternary phase diagrams is reported. The gradients are created in standard X-ray capillaries. ¹⁴C labeling and X-ray transmission measurements are used together in situ to obtain the exact sample composition along the gradient. Structural phase identification is obtained from SAXS analysis. Using this method, two cationic surfactant/glycolipid/water ternary systems have been investigated at different temperatures.

We establish experimentally the equation of state relating pressure and composition of a ternary model glycolipid/synthetic cationic surfactant/water system at room temperature. It is shown that an adhesion energy induced by the sugar headgroups is necessary to explain the presence of two distinct critical points that close two biphasic lamellar−lamellar zones. Between these two critical points, a turbid single-phase region is evidenced.

TAC8 is a new surfactant molecule. Two octyl chains form the hydrophobic part of the molecule whereas the hydrophilic part is made of two glucose groups and a cyclam ring, which gives the molecule a potential for complexing metal ions or compounds. Aqueous solutions of pure TAC8 and of TAC8 with equimolar complexed CuF2 are studied using small-angle neutron and X-ray scattering. The shape and dimensions of the micelles are determined from the scattering data using two different approaches. The first approach is model independent and uses indirect Fourier transformation of the scattering data followed by square-root deconvolution of the obtained pair-distance distribution function in order to determine the scattering length density profile. In the second approach a molecular constrained model of the micelles is fitted to the X-ray and neutron scattering data simultaneously. The results of these two different approaches agree very well. The analysis shows that both the pure TAC8 and the TAC8 with complexed CuF2 aggregate into short cylindrical micelles with aggregation numbers of approximately 20. The micelles of TAC8 with CuF2 are quite monodisperse in the concentration range studied, and their effective charge is very low compared to that of typical ionic micelles.

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A better understanding of colloidal macrostructure of the heavy petroleum products and their complex fractions is of great importance in the context of industrial problems that arise during the crude oil production, refining and transport. Much effort has been devoted to the chemical structure studies, but there is a need for more precise data regarding parameters that characterize those complex systems. For instance, the molecular weight of heavy molecules, the composition and size of aggregates formed during the industrial processing and their evolution upon the variation of temperature, pressure and with the addition of solvent have not been well known. In this paper we present new results obtained using several powerful techniques. Scattering methods (using X-rays and neutrons) are applied to study both the fractionated products (asphaltene and resin solutions in more or less good solvents) and the real systems (Safaniya vacuum residue). The lamellar structural model for asphaltenes and resins is confirmed and the molecular weight of these species determined using a polydisperse size distribution. Discussion is presented concerning the specificity of X-ray and neutron scattering : X-ray experiments are more sensitive to the aromatic-rich regions, whereas the neutron scattering data provide information about all the particle volume. Viscosimetry measurements provide information on the molecular shape of asphaltene and confirm the disk-like model. Critical micellar concentration has been obtained using Vapour Pressure Osmometry (VPO) for asphaltene suspensions in toluene and in pyridine. The resin molecules are smaller than asphaltenes, and appear to be a good solvent for asphaltenes. One of the major conclusions of this work is the wide-spread presence of density heterogeneities in diluted solutions of asphaltenes and resins as well as in the pure product (Safaniya vacuum residue). This was deduced from the scattering experiments and cryo-scanning electron microscopy data. The heating effects. were studied: a temperature increase leads to the decrease of molecular weight, but heterogeneities remain present. The structure of vacuum residue exhibits large density fluctuations which are thermally stable. These dense regions remain connected into a network up to 393°K and determine the yield value of the rheological behaviour.