Valérie Cabuil

Magnetic colloidal properties of ionic ferrofluids

Abstract 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.

Microfluidics in Inorganic Chemistry

The application of microfluidics in chemistry has gained significant importance in the recent years. Miniaturized chemistry platforms provide controlled fluid transport, rapid chemical reactions, and cost-saving advantages over conventional reactors. The advantages of microfluidics have been clearly established in the field of analytical and bioanalytical sciences and in the field of organic synthesis. It is less true in the field of inorganic chemistry and materials science; however in inorganic chemistry it has mostly been used for the separation and selective extraction of metal ions. Microfluidics has been used in materials science mainly for the improvement of nanoparticle synthesis, namely metal, metal oxide, and semiconductor nanoparticles. Microfluidic devices can also be used for the formulation of more advanced and sophisticated inorganic materials or hybrids.

Co(II) removal by magnetic alginate beads containing Cyanex 272

In this study, a series of batch experiments is conducted to investigate the ability of magnetic alginate beads containing Cyanex 272 to remove Co(II) ions from aqueous solutions. Equilibrium sorption experiments show a Co(II) uptake capacity of 0.4 mmol g(-1). The data are successfully modelled with a Langmuir equation. A series of kinetics experiments is then carried out and a pseudo-second order equation is used to fit the experimental data. The effect of pH on the sorption of Co(II) ions is also investigated. Desorption experiments by elution of the loaded beads with nitric acid at pH 1 show that the magnetic alginate beads could be reused without significant losses of their initial properties even after 3 adsorption-desorption cycles.

Phase diagram of an ionic magnetic colloid: Experimental study of the effect of ionic strength

Abstract 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.

Chitosan/maghemite composite: A magsorbent for the adsorption of methyl orange

In this study, magnetic beads were prepared by encapsulation of magnetic nanoparticles in epichlorohydrin cross-linked chitosan beads. Their adsorption characteristics were assessed by using methyl orange (MO) as an adsorbate. MO adsorption onto chitosan beads was found to be optimal in the pH range of 3-5. The adsorption isotherm was well described by the Langmuir model and showed high MO adsorption capacity (2.38 mmol/g, i.e. 779 mg/g). MO adsorption kinetics followed a pseudo-second-order kinetic model, indicating that adsorption was the rate-limiting step. At 0.305 mmol/L, only 19 min was required to reach 90% adsorption and 50% of the MO was adsorbed in 2 min. Desorption studies of MO using NaOH showed the reusability of the magsorbent. No release of iron species was observed at pH>2.4.

Static and dynamic structural probing of swollen polyacrylamide ferrogels

The local structure of hybrid ferrogels resulting from the incorporation of γ-Fe2O3 nanoparticles into a polyacrylamide polymeric network is probed from a static and a dynamic point of view, under various synthesis conditions and at swelling equilibrium. Relaxation of magneto-optical birefringence and small-angle neutron scattering measurements show adsorption of the nanoparticles onto the polymer, which is ascribed to H-bonding. These measurements allow one to identify the conditions leading either to a homogeneous scaffold reinforced by the nanoparticles, or to a nano-structured composite with 2D nanoparticle decoration on the walls of percolating pockets, initially filled by the ferrofluid during the synthesis and leaking out during the swelling. Two parameters rule the structure and the properties of these ferrogels – the osmotic pressure ratio RΠ (ratio of the osmotic pressure of the initial ferrofluid to that of the hydrogel) and the steric parameter RS (ratio of the nanoparticle volume to the mesh volume of the polymeric hydrogel).

Highly porous and monodisperse magnetic silica beads prepared by a green templating method

We describe the preparation of magnetic silica nanocomposite millimetric beads using alginate as a green biopolymer template. The simple and soft method which is used here is particularly suitable since the alginate template allows a multiscale control of the structure of the material, both its morphological characteristics at the millimetric scale and its porosity at the nanometric level. These nanocomposites are characterised by a high monodispersity, a perfect spherical shape, a very large and multiscale porosity with pore diameters ranging from 2 nm to more than 50 nm, a homogeneous dispersion of the magnetic nanoparticles in the silica matrix and a high magnetic susceptibility which increases linearly with the volume fraction of the nanoparticles. These highly porous materials which can be used as magnetic adsorbents in water treatment, showed a good sorption capacity for methylene blue, chosen as a model dye.

Polyvalent catanionic vesicles: Exploring the drug delivery mechanisms

Among drug delivery systems, catanionic vesicles now appear as powerful candidates for pharmaceutical applications because they are relatively cheap and easy to use, thus well corresponding to industrial requirements. Using labelled vesicles made of a tricatenar catanionic surfactant, the work reported here aims at exploring the mechanisms by which internalisation into a cell occurs. The study was performed on various cell types such as phagocytic as well as non-phagocytic cells using confocal laser scanning microscopy and flow cytometry. Using various inhibitors, endocytosis and also a passive process, as probably fusion, were highlighted as interaction phenomena between catanionic vesicles and cell membranes. Finally, the interaction modelled with giant liposomes as membrane models confirmed the hypothesis of the occurrence of a fusion phenomenon between the nanovectors and cell membranes. This process highlights the potential of catanionic vesicles for a future pharmaceutical application as a universal drug delivery system.

Ionic ferrofluids: Intraparticle and interparticle correlations from small-angle neutron scattering

Abstract Ferrofluids are colloidal solutions of subdomain magnetic grains dispersed in a fluid carrier. Chemically synthesized ionic ferrofluids are stabilized in aqueous media through electrostatic charges at the surface of the particles. Like binary mixtures of polymeric solutions, ferrofluids may undergo a phase separation in two coexisting liquids. We explore here the monophasic area of the phase diagram using small-angle neutron scattering from solutions of γ-Fe 2 O 3 particles of typical size 80 A in the scattering vector q range from 7 × 10 −3 to 1.3 × 10 −1 A −1 . In zero magnetic field the isolated particle behaviour is separated from the interparticle structure factor, which varies with the volume fraction up to 8% of magnetic particles.

Shape transitions of giant liposomes induced by an anisotropic spontaneous curvature.

We explore how a magnetic field breaks the symmetry of an initially spherical giant liposome filled with a magnetic colloid. The condition of rotational symmetry along the field axis leads either to a prolate or to an oblate ellipsoid. We demonstrate that an electrostatic interaction between the nanoparticles and the membrane triggers the shape transition.