Etude des propriétés structurales et magnétiques de nanoparticules de maghémite dispersées dans une matrice de silice

Les objectifs de ce travail de thèse concernent l'étude du comportement structurale et magnétique de poudres constituées de nanoparticules de maghémite (g-Fe2O3) de taille et de morphologie contrôlées (4 +- 1 nm), obtenues par coprécipitation de sels métalliques puis dispersées avec différentes concentrations dans une matrice de silice par voie sol-gel. La première partie de nos travaux a consisté à étudier la stabilité structurale des nanoparticules par irradiation laser puis en fonction de la température de traitement afin de contrôler les transitions de phase maghémite g-Fe2O3 vers l hématite a-Fe2O3 et/ou vers la phase Epsilon. La deuxième partie du travail a concerné l'étude des propriétés magnétiques des nanocomposites en fonction de la concentration massique en nanoparticules. L'objectif a été de caractériser la nature des interactions magnétiques entre les nanoparticules.The objectives of this thesis concern the study of structural and magnetic behavior of powders consisting of nanoparticles of maghemite (g-Fe2O3) of controlled size and morphology (4 +- 1 nm) obtained by coprecipitation of metal salts and then dispersed with different concentrations in a silica matrix by sol-gel process. The first part of our work was to study the structural stability of the nanoparticles by laser irradiation and depending on the temperature of treatment to control the phase transition to maghemite g-Fe2O3 into hematite a-Fe2O3 and Epsilon. The second part of the work concerned the study of magnetic properties of nanocomposites based on the mass concentration of nanoparticles. The objective was to characterize the nature of interactions between magnetic nanoparticles.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

An X-ray reflectivity study of evaporation-induced self-assembled titania-based films

X-Ray reflectivity was used to monitor the structural development of a titania-based film at the solid/air interface by evaporation-induced self-assembly (EISA). A nonionic poly(ethylene oxide)-based surfactant, Brij 58, was used as the template and titanium chloride as the inorganic precursor. The reflectivity pattern, film thickness and refractive index were shown to be dependent on film deposition method, whether by casting or by dip-coating onto a silicon wafer, the Brij 58 TiO2 ratio and the relative humidity. At Brij 58 contents of 40 wt%, the reflectivity profile displayed only a single diffraction peak. At 70 wt% Bragg diffraction indicated a lamellar ordering of film components. Modelled reflectivity data suggested a 1060 Å thick film that comprised 17 layers of alternating surfactant and titania with a d spacing of about 60 Å. The effect of relative humidity on film structure was explored

A zirconium oxide film self-assembled at the air-water interface

A self-assembled zirconia-based film, produced at the air-water interface using sodium dodecyl sulphate (SDS) as the template, has been characterised by energy-dispersive X-ray reflectometry, X-ray diffraction, and X-ray fluorescence analysis. Long-rang

Mineral phase in shell repair of Manila clam Venerupis philippinarum affected by brown ring disease

The mineral phase of shell repair in the Manila clam Venerupis philippinarum affected by brown ring disease (BRD) was characterised at various scales and at various stages of shell repair by confocal Raman microspectrometry and scanning electron microscopy. Spherulitic and quadrangular aragonite microstructures associated with polyene pigments were clearly observed. Von Kossa staining showed that at the beginning of shell repair, hemocytes are filled with insoluble calcium carbonate salts in all fluids and then are transported toward the extrapallial fluids and the repair sites. Our analyses suggest that after a Vibrio tapetis attack and BRD deposit some clams rapidly cover the deposit, resulting in a modification in the microstructure, which could be produced by the participation of both the mantle and hemocytes

Antibiofilm activity of polyamide 11 modified with thermally stable polymeric biocide polyhexamethylene guanidine 2-naphtalenesulfonate

The choice of efficient antimicrobial additives for polyamide resins is very difficult because of their high processing temperatures of up to 300 °C. In this study, a new, thermally stable polymeric biocide, polyhexamethylene guanidine 2-naphtalenesulfonate (PHMG-NS), was synthesised. According to thermogravimetric analysis, PHMG-NS has a thermal degradation point of 357 °C, confirming its potential use in joint melt processing with polyamide resins. Polyamide 11 (PA-11) films containing 5, 7 and 10 wt% of PHMG-NS were prepared by compression molding and subsequently characterised by FTIR spectroscopy. The surface properties were evaluated both by contact angle, and contactless induction. The incorporation of 10 wt% of PHMG-NS into PA-11 films was found to increase the positive surface charge density by almost two orders of magnitude. PA-11/PHMG-NS composites were found to have a thermal decomposition point at about 400 °C. Mechanical testing showed no change of the tensile strength of polyamide films containing PHMG-NS up to 7 wt%. Antibiofilm activity against the opportunistic bacteria Staphylococcus aureus and Escherichia coli was demonstrated for films containing 7 or 10 wt% of PHMG-NS, through a local biocide effect possibly based on an influence on the bacterial eDNA. The biocide hardly leached from the PA-11 matrix into water, at a rate of less than 1% from its total content for 21 days

Un établissement agricole du second âge du Fer (Bretagne, Ille-et-Vilaine, Erbrée « La Huperie »): Rapport de fouille archéologique 2017

National audienceLe site d’Erbrée « La Huperie » en Ille-et-Vilaine, a fait l’objet d’une fouille durant l’hiver 2014-2015 à l’emplacement d’une future plate-forme logistique d’Inter-Marché. Elle fait suite à un diagnostic réalisé en 2014 (Aubry, 2014). Le projet initial portant sur 24 ha, ce sont 6,25 ha qui ont été décapés dans le cadre de cette fouille. L’ensemble est situé sur un plateau à une altitude moyenne de 133 m NGF, dominant un réseau hydrologique assez fourni et reposant sur des formations limoneuses éoliennes venant recouvrir des altérites du Briovérien. Il se présente sous la forme d’une ferme indigène isolée, dont l’occupation est attestée du Hallstatt final jusqu’à la fin de La Tène finale. Quelques rares indices laissent penser à une présence humaine à l’époque antique et médiévale, sans qu’il soit possible de parler de perduration et sans que le diagnostic ait permis de localiser leur emplacement