Small angle X-Ray scattering (SAXS) on calcium sulfonate dispersions: effects of friction on microstructure

Adiabatic compressibility of AOT

The self-assembly of amphiphilic molecules into supramolecular aggregates involves a number of complex phenomena and forces. Recent developments of highly sensitive, densimetric and acoustic methods on small volume samples have provided novel sensitive probes to explore the physical properties of these complex fluids. We have investigated, by high precision densimetry and ultrasound velocimetry, reverse micelles of [sodium bis(2-ethylhexyl)sulfosuccinate] in oil (isooctane and decane), at increasing water concentration and at variable micellar volume fractions. The size of these spherical micelles has been determined by small angle x-ray scattering. Using these results, in the framework of the effective medium theory, we have developed a simple model of micellar compressibility, allowing the calculation of physical parameters (aggregation number, volume, and compressibility) of the surfactant monomolecular film as well as that of the micellar waters. In particular, we show that the central aqueous core designated as "free" water, located at a distance from the oil-water interacting interface, is twice as compressible as "bulk" water. One notable feature of this work is the influence of the nature of the oil on the above parameters.

Colloidal Sodium and Potassium Phosphates in Organic Medium: Synthesis and Analysis

Colloidal dispersions of sodium and potassium phosphates in a hydrocarbon medium have been synthesized by reacting, under specific conditions, aqueous sodium or potassium hydroxyde with tetraphosphorous decasulfide in hydrocarbon solvent in the presence of a surfactant such as alkylarylsulfonic acid. The resulting products can be defined as a distribution of inorganic particles stabilized by sodium or potassium alkylaryl sulfonate in a reverse-micelle type association. The chemical structures of the mineral cores are determined using 31P NMR, potentiometric titration and elemental analysis. The core particles were found to be respectively a mixture of sodium (poly)phosphates and a mixture of potassium (poly)phosphates. Inorganic core and organic surfactant balances were determined using thermogravimetric analysis. The weight ratio of mineral core part to organic surfactant part is found about to be 1.6 for Na derivative and 2.4 for K derivative. The morphological characterization of the colloidal dispersion has been investigated using Small Angle X-ray Scattering, Transmission Electron Microscopy and Wide Angle X-ray Scattering. The inorganic particles appear as cristallized particles with diameters ranging from 50 to 360 Å. Copyright 1998 Academic Press.