Fractal structures and silica films formed by the Treignac water on inert and biological surfaces.

The Treignac water is a natural mineral water containing mainly orthosilicic acid. On inert substrates, it forms a silica film with fractal structures which cannot be reproduced in laboratory-reconstituted water. These structures form by condensation of orthosilicic acid monomers, following the Witten-Sander model of diffusion-limited aggregation. On biological surfaces, such as tomato leaves, the Treignac water forms a silica film with a different morphology and devoid of fractal structures. The filmogenic properties of this natural mineral water are here discussed in the context of crop protection, as the silica film can provide a barrier and a platform for the immobilization of elicitors of plant defense responses.

Citrobacter freundii induced endocarditis in a yearling colt.

Endocarditis is a rare pathology in horses and the clinical signs can be misleading. We describe the clinical, echocardiographic, and pathological features of Citrobacter freundii induced bacterial endocarditis in a horse. This bacterium has never been reported before as an agent of vegetative endocarditis in the horse.

Endocardite induite parCitrobacter freundiichez un poulain âgé d'un an. L'endocardite est une pathologie rare chez les chevaux et les signes cliniques peuvent être trompeurs. Nous décrivons les caractéristiques cliniques, échographiques et pathologiques d'une endocardite bactérienne induite par Citrobacter freundii chez un cheval. Cette bactérie n'a jamais été signalée auparavant comme un agent d'endocardite végétante chez un cheval.(Traduit par Isabelle Vallières).

Interfacial reactions between humic-like substances and lateritic clay: application to the preparation of "geomimetic" materials.

The aim of this study was to understand the mechanisms responsible for the strengthening of "geomimetic" materials, especially the chemical bonding between clay and humic substances. The mineral matter is lateritic clay which mainly consists in kaolinite, goethite, hematite and quartz. The other starting products are fulvic acid (FA) and lime. The preparation of these geomimetic materials is inspired from the natural stabilization of soils by humic substances occurring over thousands of years. The present process involves acidic and alkaline reactions followed by a curing period of 18days at 60°C under a water saturated atmosphere. The acceleration of the strengthening process usually observed in soils makes this an original process for treatment of soils. The consolidation of the "geomimetic" materials could result from two major phenomena: (i) chemical bonding at the interface between the clay particles and iron compounds and the functional groups of the fulvic acid, (ii) a partial dissolution of the clay grains followed by the precipitation of the cementitious phases, namely calcium silicate hydrates, calcium aluminate hydrates and mixed calcium silicum and aluminum hydrates. Indeed, the decrease of the BET specific area of the lateritic clay after 24 h of reaction with FA added to the structural reorganization observed between 900 and 1000°C in the "geomimetic" material, and to the results of adsorption measurements, confirm the formation of organo-ferric complexes. The presence of iron oxides in clay, in the form of goethite, appears to be another parameter in favor of a ligand exchange process and the creation of binding bridges between FA and the mineral matter. Indeed all faces of goethite are likely to be involved in complexation reactions whereas in lateritic clay only lateral faces could be involved. The results of the adsorption experiments realized at a local scale will improve our understandings about the process of adsorption of FA on lateritic clays and its involvement in the strengthening process of materials.

Structural and microstructural studies of montmorillonite-based multilayer nanocomposites.

HYPOTHESES: Montmorillonite, an abundant raw material, is a good candidate to obtain textured nanocomposites. However, the resulting structure of the composite depends on the dispersant used. This work aims at investigating the effect of organic polysaccharides, namely carboxymethylcellulose (CMC) or chitosan (Ch) differing by their side groups, on the resulting structure of montmorillonite-based nanocomposites. EXPERIMENTS: The effect of sodium hexametaphosphate and of two polysaccharide derivatives (carboxymethylcellulose and chitosan) combined with montmorillonite on the structure and microstructure of resulting composite films was investigated using particle size analysis, rheological measurements, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and flexural properties measurements of the textured films. FINDINGS: Results showed that the film structure and microstructure depend on the additive. The high organization (and resulting toughness) of the montmorillonite/sodium hexametaphosphate films results from an exfoliated then layered microstructure, whereas the addition of polysaccharide derivatives leads to the particle agglomeration. In this case, two mechanisms are in competition: surface adsorption and intercalation between exfoliated platelets.

Nanocomposites derived from montmorillonite and metallosupramolecular polyelectrolytes: modular compounds for electrorheological fluids.

Nanocomposites made from Na-montmorillonite and metallo-supramolecular polyelectrolytes (MEPE) based on nickel and ditopic bis-terpyridine ligands are prepared by an aqueous synthesis. Intercalation is confirmed by IR-spectroscopy, thermogravimetric analysis, and X-ray powder diffraction. The rheological response in the presence of an electric field of the dispersed nanocomposites in silicone oil is measured with a rheometer. The nanocomposites show a distinct electrorheological effect depending on the concentration and the kind of intercalated species. The effect occurs with a low content of active material while only very small currents are observed.

Surface properties of kaolin and illite suspensions in concentrated calcium hydroxide medium.

The adsorption behaviour of calcium hydroxide onto illite and kaolin clay minerals was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clay minerals to calcium hydroxide solutions of various concentrations. Both clay minerals can adsorb calcium and hydroxyl ions. Rather than just considering proton exchanges at the clay mineral surfaces, the adsorption is explained by an approach based on Lewis description of molecules. With this approach, a mechanism for calcium hydroxide adsorption not only at the edges of the clay particles but also onto the faces is proposed. In order to gain a better insight onto the active groups at the surface of the studied clay minerals, adsorption of pyridine and ammonia on illite and kaolin was followed by FTIR spectroscopy. These measurements gave the signature of edges, which are marginally involved in interactions with calcium ions.