Dris Ihiawakrim

3D analysis of the morphology and spatial distribution of nitrogen in nitrogen-doped carbon nanotubes by energy-filtered transmission electron microscopy tomography.

We present here the application of the energy-filtered transmission electron microscopy (EFTEM) in the tomographic mode to determine the precise 3D distribution of nitrogen within nitrogen-doped carbon nanotubes (N-CNTs). Several tilt series of energy-filtered images were acquired on the K ionization edges of carbon and nitrogen on a multiwalled N-CNT containing a high amount of nitrogen. Two tilt series of carbon and nitrogen 2D maps were then calculated from the corresponding energy-filtered images by using a proper extraction procedure of the chemical signals. Applying iterative reconstruction algorithms provided two spatially correlated C and N elemental-selective volumes, which were then simultaneously analyzed with the shape-sensitive reconstruction deduced from Zero-Loss recordings. With respect to the previous findings, crucial information obtained by analyzing the 3D chemical maps was that, among the two different kind of arches formed in these nanotubes (transversal or rounded ones depending on their morphology), the transversal arches contain more nitrogen than do the round ones. In addition, a detailed analysis of the shape-sensitive volume allowed the observation of an unexpected change in morphology along the tube axis: close to the round arches (with less N), the tube is roughly cylindrical, whereas near the transversal ones (with more N), its shape changes to a prism. This relatively new technique is very powerful in the material science because it combines the ability of the classical electron tomography to solve 3D structures and the chemical selectivity of the EFTEM imaging.

Nickel hydroxide ultrathin nanosheets as building blocks for electrochemically active layers

Layered nickel hydroxides (LNHs), intercalated with lactate and nitrate anions, were synthesised using controlled precipitation and anion exchange methods. The present study reports a novel approach for the delamination of LNHs in water into nickel hydroxide nanosheets. The thickness of a single nanosheet varied between 0.7 and 1.0 nm with a lateral dimension between 50 and 80 nm. The nanosheets formed colloidal solutions or gels, retained the original hydroxide structure of LNHs, and were stable for weeks. The nanosheets were re-assembled into large-scale, well-oriented films with adjustable thickness using drop casting and spin coating techniques. The prepared nanostructured films were electrochemically active with stable and reproducible charge–discharge properties in an alkaline electrolyte. These results suggest that the nickel hydroxide nanosheets, prepared by the present methods, have potential as building blocks in the design of nanocomposite materials for energy applications.

Advanced three dimensional characterization of silica-based ultraporous materials

Whatever the field of application (building, transportation, packaging, etc.) energy losses must be reduced to meet the government target of a 40% cut in CO2 emissions. This leads to a challenge for materials scientists: designing materials with thermal conductivities lower than 0.015 W m−1 K−1 under ambient conditions. Such a low value requires reducing air molecule mobility in highly porous materials, and silica-based superinsulation materials (SIM) made of packed nanostructured silica or aerogel are good candidates for this purpose. However, the native nanostructure of silica has never been imaged or characterized up to now, making SIM optimization quite difficult. In this paper, three nanostructured commercial silica samples prepared by different synthesis methods were analysed and quantified using advanced electron tomography, N2 physisorption, mercury porosimetry and helium pycnometry. It was demonstrated that 3D images yield a much finer description of the microstructure (particle, aggregate and pore) compared to global measurements. For the samples studied, silica particle size is dependent on the synthesis method, increasing with pore diameter size. The smallest silica particles were obtained by the sol–gel method which also provides the smallest pore diameters, the smallest and rather spherical aggregates, and the lowest thermal conductivity. The pyrogenic and precipitated samples studied presented bigger silica particles with higher pore diameters and thus higher thermal conductivities. 3D image driven characterization opens up new synthesis opportunities for silica.

Spin State As a Probe of Vesicle Self-Assembly.

A novel system of paramagnetic vesicles was designed using ion pairs of iron-containing surfactants. Unilamellar vesicles (diameter ≈ 200 nm) formed spontaneously and were characterized by cryogenic transmission electron microscopy, nanoparticle tracking analysis, and light and small-angle neutron scattering. Moreover, for the first time, it is shown that magnetization measurements can be used to investigate self-assembly of such functionalized systems, giving information on the vesicle compositions and distribution of surfactants between the bilayers and the aqueous bulk.

Atmospheric plasma polymer films as templates for inorganic synthesis to yield functional hybrid coatings

Plasma polymer films produced via dielectric barrier discharge under atmospheric conditions can simultaneously host charged segments and poly(dimethysiloxane)/silica like polymers. The former segments afford some anion exchange properties and the latter ones allow stabilization of the whole coating in the presence of water. The anion exchange capacity of the film can then be used to nucleate and to grow inorganic particles in the plasma polymer coating. In particular, we exploit the presence of allylamine oligomers in a plasma coating made from a mixture of allylamine and hexamethyldisiloxane to hydrolyse titanium(IV) (bisammonium lactato dihydroxyde) and to condense it in TiO2. As a second example, Prussian Blue is produced by the successive incubation of the coating in a solution of potassium hexacyanoferrate and iron(III) chloride. The distribution of TiO2 and of Prussian Blue across the film thickness is investigated, in a semi quantitative manner, by means of Rutherford backscattering. The functional properties of the hybrid coatings are then investigated and it is found that the TiO2 containing films display photoinduced hydrophilicity whereas the films with Prussian Blue display magnetic properties.

Mimicking the chemistry of natural eumelanin synthesis: the KE sequence in polypeptides and in proteins allows for a specific control of nanosized functional polydopamine formation

The oxidation of dopamine and of other catecholamines leads to the formation of conformal films on the surface of all known materials and to the formation of a precipitate in solution. In some cases, it has been shown that the addition of additives in the dopamine solution, like certain surfactants or polymers, polyelectrolytes, and certain proteins, allows to get polydopamine nanoparticles of controlled size and the concomitant decrease, in an additive/dopamine dependent manner, in film formation on the surface of the reaction beaker. However, the mechanism behind this controlled oxidation and self-assembly of catecholamines is not known. In this article, it is shown that a specific diad of amino acids in proteins, namely KE, allows for specific control in the oxidation-self-assembly of dopamine to obtain polydopamine@protein core-shell nanoparticles which are biocompatible. The interactions between dopamine and the adjacent KE amino acids potentially responsible for the size control of polydopamine aggregates was investigated by molecular dynamics simulations. The obtained core-shell nanoparticles display the biological activity of the protein used to control the self-assembly of PDA. The photon to heat conversion ability of PDA is conserved in the PDA@protein particles.