Matériaux des nouvelles technologies pour l’énergie
Virginie Vergnat, Benoît Heinrich, Michel Rawiso, René Muller, Geneviève Pourroy and Patrick Masson
Embedding nanoparticles (NPs) with organic shells is a way to control their aggregation behavior. Using polymers allows reaching relatively high shell thicknesses but suffers from the difficulty of obtaining regular hybrid objects at gram scale. Here, we describe a three-step synthesis in which multi-gram NP batches are first obtained by thermal decomposition, prior to their covalent grafting by an atom transfer radical polymerization (ATRP) initiator and to the controlled growing of the polymer shell. Specifically, non-aggregated iron oxide NPs with a core principally composed of γ-Fe2O3 (maghemite) and either polystyrene (PS) or polymethyl methacrylate (PMMA) shell were elaborated. The oxide cores of about 13 nm diameter were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). After the polymerization, the overall diameter reached 60 nm, as shown by small-angle neutron scattering (SANS). The behavior in solution as well as rheological properties in the molten state of the polymeric shell resemble those of star polymers. Strategies to further improve the screening of NP cores with the polymer shells are discussed.
https://doi.org/10.3390/nano11092453
Fengjiao Qian, Lars J. Bannenberg, Heribert Wilhelm, Grégory Chaboussant, Lisa M. Debeer-Schmitt, Marcus P. Schmidt, Aisha Aqeel, Thomas T. M. Palstra, Ekkes Brück, Anton J. E. Lefering, Catherine Pappas, Maxim Mostovoy, Andrey O. Leonov
The lack of inversion symmetry in the crystal lattice of magnetic materials gives rise to complex noncollinear spin orders through interactions of a relativistic nature, resulting in interesting physical phenomena, such as emergent electromagnetism. Studies of cubic chiral magnets revealed a universal magnetic phase diagram composed of helical spiral, conical spiral, and skyrmion crystal phases. We report a remarkable deviation from this universal behavior. By combining neutron diffraction with magnetizationmeasurements, we observe a newmultidomain state in Cu2OSeO3. Just below the upper critical field at which the conical spiral state disappears, the spiralwave vector rotates away from the magnetic field direction. This transition gives rise to large magnetic fluctuations. We clarify the physical origin of the new state and discuss its multiferroic properties.
| The chemical bonding in actinide compounds is usually analysed by inspecting the shape and the occupation of the orbitals or by calculating bond orders which are based on orbital overlap and occupation numbers. However, this may not give a definite answer because the choice of the partitioning method may strongly influence the result possibly leading to qualitatively different answers. In this review, we summarized the state-of-the-art of methods dedicated to the theoretical characterisation of bonding including charge, orbital, quantum chemical topology and energy decomposition analyses. This review is not exhaustive but aims to highlight some of the ways opened up by recent methodological developments. Various examples have been chosen to illustrate this progress. |
|
Cooperation between research teams from the CEA, the CNRS and the Université Paris-Sud[1] has resulted in research showing that chemistry tools subjected to radiation make it possible to study the ageing of electrolytes in lithium-ion accumulators. In particular, accelerated ageing can be produced in electrolytes for the purpose of facilitating studies of their life span. This research was published in Nature Communications on 24 April 2015. Furthermore, the technique can also provide a more accurate understanding of the chemical mechanisms at work in accumulators so as to extend their life span and make them safer to use. |
|
L'utilisation de silicium à l'anode des accumulateurs Li-ion permet de fortement augmenter leur capacité. Cependant ce matériau se révèle fragile et les accumulateurs résistent mal aux cycles charge-décharge répétés. D'où l'idée d'utiliser du silicium sous forme de particules nanométriques, encapsulées dans une coquille de carbone. Le cœur de silicium offre une importante capacité spécifique (~ 10 fois celle du carbone actuellement utilisé), tandis que la coquille de carbone renforce la résistance mécanique des particules. S'appuyant sur son savoir-faire dans la réalisation de nanoparticules par pyrolyse laser, le groupe Édifice Nanométrique (EDNA) du Laboratoire Francis Perrin (LFP) a développé un nouveau montage de pyrolyse laser à "double-étage" indépendants pour la réalisation des nanoparticules de type cœur-coquille Si@C. Les premiers résultats obtenus, avec ces nanoparticules comme matériau actif dans une anode de pile, montrent une stabilité des cycles de charge/décharge sur plus de 500 cycles, pour une capacité de charge limitée à 1000 mAh/g. Ces résultats très encourageants, ont été obtenus dans le cadre d'une collaboration DSM/IRAMIS et le DRT/LITEN, et ont fait l’objet de deux dépôts de brevet. |
