HRTEM and EELS study of Y2O3/MgO thin films.

Y2O3 thin films deposited on (001)-MgO substrate have been investigated by high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy. Digital processing of the HRTEM images reveals the presence of grains with a crystallographic structure different from that of the rest of the film (Ia3). The spectrum imaging technique has been applied in vicinity of the Y2O3/MgO interface to get a better knowledge of the phases nucleated on the substrate surface. Fine structures of the O K-edge have been studied in detail; actually two kinds of spectra have been detected in the yttrium oxide thin film. These spectra have been compared to self-consistent full multiple scattering calculations (SC-FMS). One family of spectra has then been associated to the well-known Ia3 structure. The other family of spectra has been compared to calculations performed for the other known structures (such as hexagonal or monoclinic) of Y2O3 with a little success. We have finally compared these spectra to calculations performed with a particular atomic arrangement (octahedral) of Y and O atoms, which leads to a good match between experimental and calculated spectra. Our results emphasize the benefit of coupling several techniques such as HRTEM, EELS and SC-FMS for the determination of structures at the nanometric scale.

New pseudo-stationary phases for electrokinetic capillary chromatography. Complexes between bovine serum albumin and sodium dodecyl sulfate.

The complexes formed between a protein (bovine serum albumin, BSA) and a surfactant (sodium dodecyl sulfate, SDS) were studied as separation carriers in electrokinetic chromatography. Selectivities different from those with either SDS or BSA alone in the background electrolyte (BGE) were obtained. Separation performances were demonstrated to be closely related to the type of complex formed, as predicted by the isotherm curve of SDS on BSA. For each composition of background electrolyte, capacity factors and resolutions were calculated. We compared the results with these complexes to electropherograms using BGE containing either BSA or SDS alone. The separation of a mixture of phenols indicate that some compositions of the BSA-SDS complexes are efficient selectors.

Counterion Effects in Aqueous Solutions of Cationic Surfactants: Electromotive Force Measurements and Thermodynamic Model.

EMF measurements have been performed to study the influence of counterions in aqueous solutions of ionic surfactants in which the amphiphile is an n-alkyltrimethylammonium cation. General rules of variation were observed for the activities of the amphiphilic ion and the counterion, as a function of the global concentration of the surfactant salt. This study also allows us to have access to the degree of counterion binding beta over a wide range of counterions (bromide, chloride, fluoride, hydroxide, nitrate, acetate, benzoate). A systematic correlation between the concentrations of an amphiphilic cation and a counterion in solution has been established when the micellization process occurs. This correlation is also verified when a background electrolyte with a common anion is added to the surfactant solution. The mathematical relation translating the real link between concentrations of both ions of the micellar salt, deduced from this correlation, emphasizes the existence of a condition of micellization, in the form of a micellization product. A new thermodynamic model based on the electrochemical equilibrium of a dispersed phase (pseudo-phase) is developed, and we justify the existence of this condition of micellization or micellization product. Furthermore, this model is shown to be well adapted for the description of the whole phenomena observed in micellar solutions. Copyright 1999 Academic Press.