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High quality CoFe2O4 nanoparticles were synthesized only in 16 min, continuously in two coupled microreactors. The first microreactor induced the fast homogenization of the reagents mixture at ambient temperature so Fe3+ and Co2+ hydroxides precipitate, while a second microreactor heated at 98 °C allowed the fast aging and the evolution of amorphous hydroxides into faceted and crystalline CoFe2O4.

International audience; Encapsulation of non-aqueous magnetic fluids is described. The magnetic capsules thus obtained have a diameter of the order of a micron and are dispersed in water. The magnetization curves of the suspensions of magnetic capsules have been compared to the magnetization curves of the initial magnetic fluid to determine stability of this ferrofluid in the encapsulated droplets.

This letter describes how composite material, made of maghemite (γ‐Fe2O3) nanoparticles embedded in a silica∕titania matrix, can be used to develop new magneto-optical planar waveguides. Thin film samples are coated on Pyrex™ substrates from a magnetic particles doped sol-gel preparation. M-lines spectroscopy measurements performed on these samples show that an out of plane magnetic field applied during the gelation induces a decrease of the planar waveguide phase mismatch. Free space measurements evidence the Faraday rotation of the films up to 25°∕cm at 633 nm. Improvements and leads of further works are proposed in term of magneto-optical waveguide applications.

The alignment of magnetic colloidal particles along a magnetic field induces a briefringence of the solution. Static measurements of this birefringence with the field allow a determination of the size distribution of the grains. As the magnetic field is switched off, the birefringence relaxes to zero with a characteristic time proportional to the viscosity of the solution: we built up a viscometer working over 7 decades and with a 5% accuracy.

The colloidal stability of an ionic ferrofluid is ensured by a balance among magnetic, van der Waals, and screened electrostatic interactions of particles. Modifications of this subtle balance through variations of temperature, ionic strength, or magnetic field induce a phase separation into two magnetic liquids, one rich and one poor in colloidal particles. The phase separation in zero magnetic field of an ionic ferrofluid is experimentally studied here as a function of the ionic strength of the solution. A reduced phase diagram is built up. Particle concentrations in the dilute and in the concentrated phase as well as the volume ratio of these two phases are predicted from three initial independent parameters: ionic strength, total concentration of magnetic particles, and their size characteristics. This phase diagram is related to a high-order moment (≈3) of the particle size distribution and thus it is possible to realize a size sorting of particles. All these results are compared to existing theories predicting such a liquid-gas-like transition in ionic and magnetic colloids.

Magnetic properties of colloidal suspensions of γ-Fe 2 O 3 particles, obtained through a chemical synthesis, are investigated. Using an optical technique it is verified that these ionic aqueous ferrofluids are stable in high fields. The magnetization saturation of the particles is found independent of their size. Electron microscopy, magnetization and birefringence measurements allow us to separate the two superparamagnetic processes existing in such ferrofluid solutions: Bulk and Neel rotations. The Neel process is investigated through remanent magnetization of frozen solution.

Lors de la precipitation, en milieu alcalin, de sels ferreux et ferriques, le rendement en materiau magnetique (magnetite, berthollide, maghemite) et la taille des particules obtenues, augmentent avec la fraction molaire initiale en Fe(II) et dependent de la nature du milieu alcalin. Une valeur elevee du pH (superieure a 9,6) et la presence de cations (en particulier de NH 4 + , pour des syntheses dans l'ammoniac) orientent la synthese vers la goethite coexistant avec des particules magnetiques de petit diametre

We study ionic magnetic colloidal dispersions, which are constituted of g-Fe2O3 nanoparticles dispersed in water, and stabilized with electrostatic interparticle repulsion. The phase diagram PV versus F (P: osmotic pressure, V: particle volume, F: particle volume fraction) is explored, especially in the range of high P and high F. The osmotic pressure P of the colloidal dispersion is known either by a measurement either because it is imposed during the sample preparation by osmotic compression. The structure of the colloidal dispersion is determined from Small Angle Neutron Scattering (SANS). Two regimes can be distinguished. At high pressure, fluid and solid phases can exist. Their structure is governed by strong electrostatic repulsion, the range of which is here evaluated. At low pressure, gas, liquid and glassy solids can exist. Their structure results from a sticky hard sphere potential.

International audience; Diblock copolymers are known to self-organize in ordered domains. The morphology of this microphase separation depends essentially on the relative amount of each immiscible block in the copolymer (e.g. spherical, cylindrical, gyroidal and lamellar phases). The lamellar nanoscopic structures can serve as templates for the selective incorporation of inorganic nanoparticles , , for instance to get nanopatterned surfaces or for new applications such as wave guides. , In most of the studies concerning diblock copolymer self-assembly in lamellar periodic structures, diblock copolymers were synthesized by anionic polymerization which is a suitable technique to prepare well-defined high molar mass diblock copolymers. , In the present study, our aim is the synthesis of high molar mass poly(n-butyl methacrylate)-b-polystyrene diblock copolymers by Atom Transfer Radical Polymerization (ATRP). Compared to anionic polymerization, controlled radical polymerization (CRP) is a more versatile technique which requires less drastic experimental conditions. Our results highlight the self-assembly of the symmetric poly(n-butyl methacrylate)-b-poly(styrene) diblock copolymer synthesized by ATRP into a lamellar ordered structure after an annealing treatment.

Mesophase templated silica layers seeded with magnetic or non magnetic nanoparticles are prepared. The study of the interactions between the nanoparticles and the others compounds of the synthesis solution is first described to explain the synthesis conditions allowing a homogeneous seeding. X-ray diffraction measurements are then used to study the texture of thick layers seeded with magnetic nanoparticles.

International audience

In the context of the project of sodium fast reactor ASTRID, CEA is currently developing new analytical techniques to monitor the chemical purity of liquid sodium. Indeed, incidental situations occurring in the reactor, such as fuel clad failures, leakages in the steam generator or in the coolant pumps, and accelerated corrosion, might release several elements in the sodium. Analytical techniques based on laser ablation and emission spectroscopy are well suited for this application. They do not require any sample preparation, and can perform direct on-line analysis. Amongst them, Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation coupled to Laser-Induced Fluorescence (LA-LIF) have been selected for this study. The objective of this work was to characterize the sensitivity of those two techniques for the detection of impurities in liquid sodium. Their limits of detection were calculated for model analytes using calibration lines. Then results were theoretically extrapolated to other analytes of interest. This study shows the feasibility of the detection of steel corrosion products in liquid sodium. However, the LIBS technique is more robust and easier to implement, and would therefore be more suited to nuclear conditions., Dans le cadre du projet de réacteur nucléaire à neutrons rapides et caloporteur sodium baptisé ASTRID, le CEA cherche à développer des techniques d'analyse innovantes afin de surveiller la pureté chimique du sodium liquide. L'objectif est de détecter des situations incidentelles telles que les ruptures de gaine, les fuites dans le générateur de vapeur ou dans les pompes du circuit primaire, et la corrosion accélérée, qui entraînent la contamination du caloporteur par certains éléments. Les techniques d'analyse élémentaire basées sur l'ablation laser et la spectroscopie d'émission sont particulièrement adaptées à cette problématique, car elles permettent de réaliser des mesures directes et à distance de tout type d'échantillons. Parmi elles, la spectroscopie sur plasma induit par laser (LIBS) et l'ablation laser couplée à la fluorescence induite par laser (LA-LIF) ont été sélectionnées pour cette étude. L'objectif de cette thèse est la détermination de la sensibilité de ces deux techniques pour la détection d'impuretés dans le sodium liquide. Les limites de détection de la LIBS et de la LA-LIF sont calculées pour des analytes modèles à partir du tracé de droites d'étalonnage. Elles sont respectivement de l'ordre de la ppm massique et de l'ordre de la centaine de ppb massiques. Ces résultats sont ensuite extrapolés théoriquement aux autres analytes d'intérêt. Les résultats montrent la faisabilité de la détection et du suivi des concentrations des produits de corrosion des aciers dans le sodium liquide. Cependant, la LIBS est plus robuste et plus simple de mise en oeuvre et serait par conséquent mieux adaptée à une implantation en centrale nucléaire.

This manuscript describes ten years of research performed at the Pierre & Marie Curie University (Paris 6) then at the University of Bordeaux on composite materials based on magnetic iron oxide nanoparticles dispersed in a matrix, most often of polymer, but also sometimes of liquid crystal, with various sizes and shapes (gels, films, micron scale beads, micelles or vesicles...). The projects belong to the domain of medical imaging, and to pharmaceutical active delivery triggered magnetically. The annex file presents works anterior (1995-2001) and posterior (2012-2021) to this habilitation thesis.; Ce manuscrit décrit dix années de recherche effectuées à l’université Pierre et Marie Curie puis à l’université de Bordeaux sur des matériaux composites à base de nanoparticules d’oxyde de fer magnétique dispersées dans une matrice, le plus souvent polymère, mais aussi parfois cristal liquide, de tailles et de formes variées (gels, films, billes micrométriques, micelles et vésicules…). Les projets s’inscrivent dans le domaine de l’imagerie médicale et la délivrance d’un actif pharmaceutique contrôlée magnétiquement. Le fichier annexe présente les travaux antérieurs (1995-2001) et postérieurs (2012-2021) à cette HDR.

The goal of this work is to prepare and study a magnetic composite material capable of adsorbing organic molecules. This work takes part in the development of new pollution-reduction methods through magnetic separation.The composite material is synthesised by encapsulating iron oxide nanoparticles and activated carbon particles within alginate beads. Alginate is a natural polysaccharide produced by brown algae that can form a gel in presence of divalent cations such as calcium ions. Iron oxide nanoparticles are used in the form of a stable colloidal suspension called a ferrofluid. The nanoparticles are synthesised by coprecipitating Fe(II) and Fe(III) ions with ammonia. After an oxidation step leading to the formation of maghémite (Γ-Fe2O3), the nanoparticles are functionalised by citrate ions in order to stabilise them in a neutral solution. The inclusion of activated carbon particles in the polymer matrix allows for the efficient removal of organic molecules by adsorption.Several formulations are used for the preparation of the beads. Different amounts of iron oxide nanoparticles or activated carbon particles are encapsulated in the alginate beads. Variation of the formulation also includes the chemical modification of the polymer matrix: alginate is either reticulated by calcium ions or with a bifunctional organic molecule, epichlorohydrin. Finally, the beads are used directly after their preparation in a humid form or are dried in an oven.Chemical characterisation of the beads shows that encapsulation of the precursors is total, with no loss of materials with time. Determination of the amounts of calcium and sodium cations within the beads allows for the quantification of negative charges borne by alginate and the citrate-functionalised iron oxide nanoparticles. Physical characterisation includes the study of the porosity of the beads and the determination of their magnetic properties. The beads are found to be superparamagnetic, with characteristic parameters close to those of the ferrofluid precursor: the encapsulation has no impact on the magnetic behaviour of the iron oxide nanoparticles.Adsorption properties of the beads are evaluated through the adsorption of two organic dyes, negatively-charged methyl orange and positively-charged methylene blue. Adsorption at equilibrium is studied by building adsorption isotherms: these curves give access to the adsorption capacity of the beads, which is compared to the capacity of the precursors, and gives hints of the adsorption mechanisms involved. Both dyes are found to be adsorbed on the encapsulated activated carbon through Van der Walls interactions, whereas methylene blue can also be adsorbed on alginate and on the iron oxide nanoparticles through ion-exchange interactions with sodium and calcium ions. Those two mechanisms may be modelled by independent Langmuir equations. Influence of the formulation of the beads on the adsorption capacity and the adsorption mechanisms is studied. In particular, the amount of activated carbon encapsulated within the beads directly influences the ratio of the adsorption capacities of methylene blue and methyl orange: low amount of encapsulated activated carbons allows the beads to adsorb more methylene blue than methyl orange which gives the beads some selectivity properties. Finally, the influence of external factors such as pH is studied; it is found to impact the ion-exchange reaction, but not adsorption on activated carbon.Adsorption kinetics is studied for each dye, and shows that equilibrium is reached in the scale of several hours. The variation of the amount of dye adsorbed with time may be modelled with the pseudo-second order equation as well as the intraparticular diffusion model. This highlights the need to control precisely the porosity of the composite material the speed up the adsorption reaction.Finally, comparison with existing adsorption materials shows that our composite beads have an interesting potential for use in adsorption, with good adsorption capacities, ability to modulate selectivity and additional magnetic properties that may be useful in innovative industrial processes., Ce travail de recherche s'intègre dans un projet de développement d'un procédé de traitement des effluents par séparation magnétique s'inscrivant dans une démarche d'écoconception. Pour ce faire, nous avons préparé des billes d'alginate encapsulant des nanoparticules magnétiques et du charbon actif. Les matériaux composant ces billes possèdent des propriétés adsorbantes permettant l'extraction de polluants ; leurs propriétés magnétiques permettent de les séparer magnétiquement de l'effluent à traiter. La formulation et la caractérisation des billes magnétiques est le point essentiel de ce travail. Différentes formulations ont été testées en modifiant les quantités de matériaux précurseurs ainsi que le mode de réticulation de l'alginate. Les capacités d'adsorption des billes vis-à-vis de deux colorants utilisés comme modèles de polluant organique, le bleu de méthylène et le méthyl orange, ont été étudiées. La modélisation des isothermes d'adsorption a permis également de comprendre les mécanismes mis en jeu. Les cinétiques d'adsorption ont également été étudiées et modélisées.

The unique properties of supercritical fluids (SCFs) have been widely used since the 1980’sin a wide range of applications including separation, chemistry and materials synthesis.Currently, the research activities are focused toward a better understanding and tailoring ofthermodynamical, physical and chemical phenomena involved in SCFs processes. In thiscontext, this is why we have chosen to develop supercritical microfluidics in the frame of thisPhD work, which aims at developing and using microfluidic tools in order to study the chemicalreactivity and the nucleation-growth in supercritical fluids.First of all, our strategy aimed at fabricating microsystems which could handle to the SCFsoperating conditions (high pressure and high temperature). Then, we have studied somephysical characteristics of these devices and in particular we determined the expectedadvantages associated with the combination of microfluidic tools and supercritical fluids.Afterwards, we have demonstrated the benefits of the supercritical microfluidics to materialssynthesis and chemical reactivity through the hydrothermal oxidation of methanol and thesynthesis of ZnO nanocrystals. This last point was also the subject of a photoluminescencestudy, demonstrating that supercritical microfluidics tools can be used as “precision synthesis”reactors., Les propriétés spécifiques des milieux fluides supercritiques sont exploitées depuis denombreuses années dans les domaines de la séparation, de la chimie et des matériaux.Aujourd’hui, les activités de recherche se focalisent vers une meilleure compréhension et unmeilleur contrôle des processus thermodynamiques, physiques et chimiques mis en jeu, ce quinous a naturellement amené à développer la microfluidique supercritique. C’est dans cecontexte que s’inscrivent ces travaux de thèse ayant pour objet le développement et l’utilisationde l’outil microfluidique pour l’étude de la réactivité chimique et de la germination-croissance enmilieux fluides supercritiques.Notre premier objectif a concerné le développement de l’outil microfluidique supercritique etde microsystèmes résistants aux conditions de température et de pression. Quelquescaractéristiques physiques associées à ces dispositifs sont proposées de manière à observerclairement les avantages attendus du couplage de la microfluidique et des fluides supercritiques.Nous avons ensuite validé l’apport de la microfluidique supercritique sur la réactivité chimiqueet la chimie des matériaux via, d’une part, l’étude de l’oxydation hydrothermale du méthanol et,d’autre part, l’élaboration de nanocristaux de ZnO. Les propriétés de photoluminescence de cesnanocristaux de ZnO ont été caractérisées; nous avons montré que l’outil microfluidiquesupercritique permet de synthétiser des nanocristaux de ZnO avec une luminescenceexcitonique.

This work deals with the insertion of inorganic nanoparticles inside onion-type multilamellar vesicles. Intravesicular synthesis of gold nanoparticles was performed via three paths: chemical reduction, UV photoreduction and gamma radiolysis. Control of nanoparticles morphology via chemical composition of vesicles was demonstrated for chemical reduction. Whatever the synthetic path, onion stability depends on the number and the size of synthesized particles. Such an organic/inorganic hybrid, onion/nanoparticles (gold and silver), was tested for heterogeneous catalysis. Magnetic onions were also elaborated via two methods: intravesicular synthesis of magnetic nanoparticles and ferrofluid encapsulation. Magnetic properties of onions, as contrast agent for MRI and for hyperthermia, were measured., Ce travail de thèse a porté sur l'incorporation de nanoparticules inorganiques au sein de vésicules multilamellaires lipidiques de type " oignon ". La synthèse intravésiculaire de nanoparticules d'or a été réalisée par voie chimique, photoréduction UV et radiolyse gamma. Nous avons montré qu'il est possible de contrôler la morphologie des particules par la composition vésiculaire dans le cas d'une réduction chimique. Quelle que soit la voie de synthèse, nous avons établi que la stabilité de l'oignon dépend de la taille des nanoparticules qu'il contient et de leur nombre. L'utilisation de ces structures hybrides,oignons/nanoparticules (or et argent), pour la catalyse supportée a été abordée. Nous avons également élaboré des oignons magnétiques selon deux voies: par synthèse intravésiculaire de nanoparticules magnétiques et par encapsulation d'un ferrofluide. Les propriétés des oignons en terme de magnétisme, d'hyperthermie magnétique et d'agents de contraste pour IRM ont été étudiées.