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This high resolution small angle X-ray scattering study of a concentrated oxide sol, precursor of the SYNROC matrix for the storage of the high level radioactive waste, evidences a locally cylindrical microstructure. Locally, nanometric cylinders show disordered axis with some concentration dependent connections. This microstructure explains the paradoxical stability of this oxide dispersions. This stability has a steric origin and electrostatic repulsions are not needed. The addition of aluminium to the initial titanium-zirconium mixture enhances branching on the locally cylindrical microstructure. Finally, we show that the solid powder obtained after drying of the sol has the same specific area (∼ 1000 m2/g) as the sol. [ABSTRACT FROM AUTHOR]

The occurrence of a critical point in smectic liquid crystal is experimetnally evidenced by i) broadening of the Bragg peak of the coexisting lamellar phases, and ii) strong scattering at low angle in the vicinity of the critical point, where the concentration and periodicity difference between the two phases in equilibrium vanishes. First approximate values of the critical exponents are given. [ABSTRACT FROM AUTHOR]

This is a preliminary report about new osmotic pressure measurements in electrostatically stabilized highly swollen lamellar phases. We identify the stabilizing forces for different regimes: the equilibrium between dispersion and electrostatic forces explains the two coexisting lamellar phases while the lamellar to asymmetric disordered lamellar phase transition is entropically driven. [ABSTRACT FROM AUTHOR]

The AO:T water/oil microemulsions exhibit a percolation process which leads to the formation of aggregates when temperature or water droplets concentration increase. In the presence of cytochrome c, this aggregation process is more efficient. In order to know the influence of this protein on the structure of the aggregates so formed, we report structural studies by SAXS. The reuslts show that the aggregates behave like polymer solutions in semidilute regime. [ABSTRACT FROM AUTHOR]

Asphaltenes, defined as the fraction insoluble in n-heptane, are responsible for flocculation of crude oil. We consider both crude oil and asphaltene solutions as dynamical colloidal systems containing particles that may form different aggregates upon changing the temperature and polarity of the solvent. For example, resins, the polar molecules present in crude oils, constitute a good solvent for asphaltenes. We used ultra small-angle x-ray scattering (USAXS) in order to investigate the evolution of the macrostructure of asphaltenes, resins, and crude oils. This technique enables to investigate particles of the size range 10-10000 Å. We have studied a simplified system composed of asphaltenes and resins in a toluene solution, as well as the vacuum residue that contains asphaltenes, resins, aromatics, and saturated species. An important finding is the presence of large-size fluctuations of concentration in the temperature region 200°∮300°C. The stability of agglomerates is caused by covalent bonding. However, we observe the decrease of aggregate size for asphaltenes and resins at higher temperatures. The rheology results confirm flat shape of the asphaltene's aggregates. The effect of temperature is particularly pronounced for small aggregates of asphaltene molecules. [ABSTRACT FROM AUTHOR]

We examine the solubilization of a lipophilic molecule (lindane) in the nonionic system water-oil-CiEj, particularly in the microemulsion domain. Solubilization of lindane in this ternary system induces a variation of the HLB temperature and of the efficiency of the surfactant. The temperature of hydrophilic-lipophilic balance (HLB), or better, the temperature of zero spontaneous curvature T of the film, increases or decreases depending on the relative penetration power of oil and solute (lindane) in the amphiphilic film. We observe an excess solubility of lindane in the microemulsion regime, compared to bulk oil at the same temperature. This allows direct determination of the lindane excess adsorbed in the interfacial film referring to a temperature of the zero average curvature. No area per molecule variation associated to lindane penetration could be detected. [ABSTRACT FROM AUTHOR]

The local structure of titania/zirconia colloids has been investigated using small-angle neutron scattering (SANS). The colloids were produced by:• hydrolysing a mixture of titanium and zirconium alkoxides, and peptising the resulting hydrolysate with nitric acid (homogeneous);• hydrolysing a titanium alkoxide, and peptising the resulting hydrolysate with aqueous zirconium (IV) nitrate solution (heterogeneous). The final titania/zirconia and metal oxide/nitrate mole ratios were 16.0 and 10.0, respectively. The results of SANS contrast variation experiments are described. The minimum-contrast points for the homogeneous and heterogeneous colloids, determined using either the known analytic form of the scattering at q=0 or the scattering invariant, gave similar results, which differed significantly from the expected value. These differences were attributed to the sorption of nitrate counter-ions and hydroxyl species on the surface of the colloids. In both cases, the scattering at minimum contrast was consistent with a fractal network of uni-dimensional zirconia, with a typical diameter of ∼1.5 nm. The results infer that in the homogeneous colloids, the zirconia is segregated within the matrix of the titania crystallites (on ∼1 nm scale), whereas in the heterogeneous colloids, the zirconia is segregated on the surface of the titania crystallites (on ∼10 nm scale). [ABSTRACT FROM AUTHOR]