Kinetic study of the reaction of leuco methylene blue with 2,6-dimethyl-p-benzoquinone in a reverse micellar system

The kinetics of the reaction of leuco methylene blue (MBH) with 2,6-dimethyl-p-benzoquinone (DMBQ) were studied in a heptane/bis(2-ethylhexyl)-sulfosuccinate (AOT)/water reverse micellar system. The pseudo-first-order rate constant (k (obsd)) obtained in the presence of excess of DMBQ was found to be proportional to the initial concentration of DMBQ for W (0)=3, 5, 10, 15 and 20 (W (0)=[H2O]/[AOT]). The second-order rate constant (k (2)=k (obsd)/[DMBQ](0)) increased with an increase in the W (0) value, but was almost independent of the concentration of the water pool. A mechanism involving the distribution of DMBQ between the reverse micellar interface and bulk organic solvent was proposed to explain these findings.</p

Collective effect on magnetic properties of 2D superlattices of nanosized cobalt particles

International audienceWe report fabrication, structural and magnetic properties of cobalt nanocrystals. They are synthesized in colloidal assemblies. The coated cobalt particles are air stable. Due to the narrow size distribution of these 8 nm particles, they self-assembled after deposition on a flat substrate. The magnetic response depends on the organization. When they are dispersed in a solution, the saturation is not reached at 2T even at 3 K, they are still a superparamagnetic part in the signal. When particles are organized in 2D superlattices, saturation is reached at lower applied field, compared to isolated particles. This is attributed to an increase of dipolar interaction. However, the hysteresis loop markedly differs with the sample orientation in the applied field. This confirms the dipolar magnetic interactions between cobalt nanoparticles

New Technique to Make Ferrite Nanosized Particles

Preparation of magnetite/maghemite nanometric particles is reported from the precipitation of ferrous dodecyl sulfate micellar solution with methylamine. The size of nanocrystals is controlled by the micellar concentration and by temperature. It varies from 3.3nm to 11nm. Magnetic properties are studied for various sizes of maghemite particles

Gold nanorods: Limitations on their synthesis and optical properties

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Micellar effects on charge separation

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The self-organization of magnetic nanoparticles : a Monte Carlo study

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Polymorphism in nanoparticle-based crystals depending upon their single or polycrystalline character

International audienceColloidal single-crystals with submillimeter size (colloidal crystal) are built by self-assembly of gold nanoparticles with nearly similar size (ca.5nm) but different nanocrystallinities. The external shape of the gold nanoparticles was characterized by electron microscopy and related to their nanocrystallinity. A synchrotron-based experiment is used to collect X-ray diffraction patterns from individual single-crystals over the wide q-range relevant to both inter-atomic and inter-particles periodicities. This makes possible a detailed reconstruction of the reciprocal space including diffuse scattering. X-ray diffraction demonstrates that colloidal crystals made of single-crystal nanoparticles belong to the body-centered cubic system while face-centered cubic single crystals are observed in case of self-assembly by polycrystalline particles; a remarkable feature is the preferential orientation of the symmetry axes of the single-crystal nanoparticles along those of the colloidal crystal; on the contrary polycrystalline nanoparticles display random orientation. These results show the importance of the nanocrystallinity for the packing behavior