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The present study aims at investigating the elaboration of a ZnO/sol–gel nanocomposite coating, which can provide a number of properties such as UV-absorption, mechanical and barrier effects, etc. depending on targeted applications. The sol–gel coating formulation is an inorganic–organic hybrid based on tetraethoxysilane (TEOS) and glycidyloxypropyltrimethoxysilane (GPTMS). In order to ensure good dispersion in the sol–gel matrix, ZnO nanoparticles were surface-modified with a silane coupling agent. The functionalization was confirmed by Fourier transform infrared (FTIR) and thermogravimetric (TGA) analyses. Field emission gun-scanning electron microscopy (FEG-SEM) characterization of the nanocomposite film reveals a homogeneous distribution and dispersion of the ZnO nanoparticles throughout the film. Glow discharge optical emission spectrometry (GDOES) analysis allows evaluating the thickness of coatings and getting a depth composition profile. Some properties such as UV-absorption and barrier effect are highlighted using a UV–visible spectrometer and electrochemical impedance spectroscopy (EIS), respectively. The effect of ZnO concentration is also presented.

Poly(e-caprolactone)-coated (covalently grafted and physisorbed) multi-walled carbon nanotubes (MWCNTs) were synthesized by ring-opening polymerization (ROP) of e-caprolactone initiated from primary amines grafted on the MWCNT surface through the exposure to atomic nitrogen generated in a microwave-induced plasma. The morphology of the recovered nanohybrids and the amount of grafted polymer chains were studied by transmission electron microscopy (TEM) and thermogravimetric analysis (TGA), respectively. These nanohybrids were used as highly filled masterbatches to be dispersed within either poly(e-caprolactone) (PCL) or high-density polyethylene (HDPE) matrices in the molten state. The thermal behavior as well as the electrical properties of the so-produced nanocomposites were characterized and correlated to their morphology. The HDPE filled with PCL-coated MWCNTs nanohybrids showed better electrical properties than HDPE filled with non-modified MWCNTs. The electrical properties improvement was associated to a better dispersion of the PCL-coated MWCNTs and, also, to the exclusive presence of PCL coating in tunneling junction between the nanotubes.

In this study, bionanocomposites based on renewable cellulose nanowhiskers (CNWs) as nanofillers and renewable poly( l -lactide) (PLA) as polymeric matrix were successfully and straightforwardly prepared using melt-extrusion technique. Due to the affinity difference between hydrophobic PLA and hydrophilic CNWs, the surface of CNWs was directly modified in aqueous suspension (pH = 5.4 – citrate buffer) at ambient temperature in the presence of functional trialkoxysilanes bearing various organic moieties (alkyl, amino, and (meth)acryloxy). The surface-functionalization of CNWs was first investigated using methacryloxy-based trialkoxysilane as model. The influence of parameters such as the amount of silane agents and the post-treatment conditions were optimized on the surface-modification of methacryloxy-modified CNWs. FT-IR, TEM, WAXS and XPS analyses provided further evidences about the efficiency of the surface-modifications of CNWs. In a subsequent step, the chemically modified CNWs were successfully incorporated into PLA by melt-extrusion in the absence of solvent, without any alterations of their nanostructure after melt-processing. The thermal/mechanical properties of the resulting bionanocomposites were determined and shown to be enhanced when silanized CNWs were used as nanofillers.

Poly(epsilon-caprolactone) (PCL) nanocomposites containing carbon nanotubes, layered silicates, sepiolite or polyhedral oligomeric silsesquioxane (POSS) were characterized by advanced thermal analysis. Adding carbon nanotubes or layered silicates increases the excess heat capacity in quasi-isothermal crystallization experiments by MTDSC, pointing to an increased fraction of reversibly melting and crystallizing material. In situ AFM during isothermal crystallization and SAXS during subsequent heating reveal an altered PCL semi-crystalline morphology. The nucleating ability of the carbon nanotubes induces a striking transcrystalline morphology, promoting the growth of secondary PCL crystals with an increased fold surface energy and a reduced melting temperature. The altered crystalline-amorphous interphase at the crystal fold surface houses the material that reversibly crystallizes and melts under quasi-isothermal crystallization conditions. A fraction of this interphase is not able to crystallize but converts into glassy, rigid amorphous material upon cooling prior to reaching the PCL main glass transition temperature. Low aspect ratio sepiolite and POSS nanofillers barely nucleate the PCL crystallization and therefore hardly affect the PCL semi-crystalline morphology and thermal behavior.

In this work, the nucleation and crystallization behavior of melt mixed PCL/CNT nanocomposites has been studied. The mixtures of PCL and pristine MWNTs were prepared by extrusion with different nanofiller contents: 0.3, 0.5, 0.7, 1 and 3%. Standard DSC measurements demonstrated pronounced nucleation effects as well as increases in PCL crystallinity. The nucleation effect saturates at only 0.5% (a value much lower than those previously reported in the literature for similar nanocomposites) indicating that the dispersions obtained were excellent. This was corroborated by both TEM observations and by the determination of a very low dielectric percolation threshold (i.e., 0.3%). In self-nucleation experiments, supernucleation effects were obtained up to a maximum of approximately 200% efficiency. This is the first time that supernucleation effects of this order have been reported for PCL filled with untreated MWNTs, a result that we attribute to the excellent dispersion achieved. Isothermal crystallization experiments performed by DSC showed an increase in the crystallization kinetics of PCL with increases in MWNT content as a consequence of the supernucleation effect. The Avrami equation successfully described the overall crystallization kinetics and while neat PCL exhibited Avrami indexes close to 3, indicating that instantaneously nucleated spherulites were formed, the nanocomposite yielded mostly Avrami index values close to 2, as expected for axialites instantaneously nucleated on the surface of the MWNTs. Remarkably, the temperature dependence of the overall crystallization rate exhibited a dramatic change with MWNT content. This novel effect was described as a crystallization regime change (i.e., from Regime II to Regime III) induced by the presence of the MWNTs in terms of the Lauritzen and Hoffman theory.

A novel strategy to graft functional groups at the surface of carbon nanotubes (CNTs) is discussed. Aiming at grafting nitrogen containing groups, and more specifically primary amine covalent functionalization, CNTs were exposed under atomic nitrogen flow arising from an Ar + N2 microwave plasma. The primary amine functions were identified and quantified through chemical derivatization with 4-(trifluoromethyl)benzaldehyde and characterized through X-ray photoelectron spectroscopy. The increase of the selectivity in the primary amines grafting onto CNTs, up to 66.7% for treatment of CNT powder, was performed via the reduction of post-treatment oxygen contamination and the addition of hydrogen in the experimental set-up, more particularly in the plasma post-discharge chamber. The analyses of nitrogenated and primary amine functions grafting on the CNT surface suggest that atomic nitrogen (N•) and reduced nitrogen species (NH• and NH2•) react preferentially with defect sites of CNTs and, then, only atomic nitrogen continues to react on the CNT surface, creating defects.

In this work, a controlled synthesis route for obtaining highly vertically aligned CNTs is reported. This route is based on the combination of the magnetron sputtering deposition to prepare the catalysts and the chemical vapour deposition (CVD) technique to synthesize the CNTs. The oxygen functionalization of the vertically aligned multi-walled carbon nanotubes (v-CNTs) was studied, aiming at determining the nature of the functional groups grafted at the tip of the CNTs. The functionalization was performed through exposure of v-CNTs to atomic oxygen generated in a micro-wave plasma. The vertical alignment of the CNTs was characterized before and after the functionalization treatment using scanning electron microscopy. Static contact angle measurements and x-ray photoelectron spectroscopy analyses were used to investigate changes induced at the tips of the CNTs due to functionalization.

Dc and ac conductivities in a broad angular frequency, 2π × 10−3 s−1 < ω < 2π × 107 s−1, and temperature range, 133 K < T < 323 K, were measured in poly(e-caprolactone)/multiwalled carbon nanotube nanocomposites as a function of weight concentration (0 wt % ≤ p ≤ 3 wt %) . The universal dynamic response was observed at low p values, and the parameters were adjusted by working in several domains. Scaling laws predicted by the variation of dc conductivity as a function of p or characteristic frequency in percolation theory were followed and showed the formation of a 3D percolative cluster at concentration values as low as 0.3 wt %. The existence of tunneling conduction was proved, and its independence on temperature indicates that we are in the presence of a conventional tunnel effect among nanoparticles not yet in physical contact, through energy barriers made by the polymer chains. All these combined facts allowed construction of a master curve evidencing the time−temperature−composition superposition exi...

In this study of the changes induced by exposing MWCNTs to a nitrogen plasma, it was found by HRTEM that the atomic nitrogen exposure does not significantly etch the surface of the carbon nanotube (CNT). Nevertheless, the atomic nitrogen generated by a microwave plasma effectively grafts amine, nitrile, amide, and oxime groups onto the CNT surface, as observed by XPS, altering the density of valence electronic states, as seen in UPS. (C) 2008 Elsevier Ltd. All fights reserved.

International audience; Shared memory MPI communication is an important part of the overall performance of parallel applications. However understanding the behavior of these data transfers is difficult because of the combined complexity of modern memory architectures with multiple levels of caches and complex cache coherence protocols, of MPI implementations, and of application needs. We analyze shared memory MPI communication from a cache coherence perspective through a new memory model. It captures the memory architecture characteristics with microbenchmarks that exhibit the limitations of the memory accesses involved in the data transfer. We model the performance of intra-node communication without requiring complex analytical models. The advantage of the approach consists in not requiring deep knowledge of rarely documented hardware features such as caching policies or prefetchers that make modeling modern memory subsystems hardly feasible. Our qualitative analysis based on this result leads to a better understanding of shared memory communication performance for scientific computing. We then discuss some possible optimizations such as buffer reuse order, cache flushing, and non-temporal instructions that could be used by MPI implementers.

Multi-walled carbon nanotubes (MWNTs) are placed under atomic nitrogen flow formed through an Ar + N2 microwave plasma in order to functionalize covalently their side walls with nitrogen-containing groups. The MWNT surface analyzed by X-ray photoelectron spectroscopy shows the presence of amides, oximes and mainly amine and nitrile functions grafted in this way. In order to highlight the actual location of the amine functions grafted on MWNTs, they were considered as initiation species in ring-opening polymerization of e-caprolactone using triethylaluminium as activator. The so-generated poly(e-caprolactone) chains remain grafted on the MWNTs via amide bonds and form polyester islets along the nanotubes surface. TEM images of these MWNT surfaces grafted with poly(e-caprolactone) show a good amino-sidewall distribution. This work demonstrates the side-wall amino-functionalization of carbon nanotubes readily achieved by microwave plasma with the possibility to reach within a short time period very high contents in nitrogen-based functions (∼10 at.%).

The chapter begins by discussing carbon nanotube (CNT) surface chemistry and solution-based functionalization. It then reviews promising alternative ways to modify the CNT surface through plasma processes. Plasma treatments have the advantage of being non-polluting and provide a wide range of grafted functional groups, depending on the plasma parameters such as power, gases used, duration of treatment and gas pressure. However, the interaction of high energy particles with the CNT surface can induce damage in the CNT structure. A plasma post-discharge treatment, which can prevent the degradation of CNTs, is presented.

International audience; Vertically aligned multiwalled carbon nanotubes (v-MWCNTs) are functionalized using atomic oxygen generated in a microwave plasma. X-ray photoelectron spectroscopy depth profile analysis shows that the plasma treatment effectively grafts oxygen exclusively at the v-MWCNT tips. Electron microscopy shows that neither the vertical alignment nor the structure of v-MWCNTs were affected by the plasma treatment. Density functional calculations suggest assignment of XPS C 1s peaks at 286.6 and 287.5 eV, to epoxy and carbonyl functional groups, respectively.

New functionalized poly(3-hexylthiophene)s (P3HT) have been designed and synthesized with the aim of increasing the dispersion of carbon nanotubes (CNT) in solutions and in thin films of semiconducting polymers. Dispersion in solution has been assessed by sedimentation tests while the thin film morphology has been analyzed by TEM and AFM. Both the physisorption of P3HT chains (via pyrene end-groups) or their chemical grafting (onto amine functions generated on the CNT surface) lead to a much better dispersion in solution and in the solid. In thin films, P3HT fibrils are observed to arrange perpendicular to the CNT surface, which can be understood on the basis of molecular modeling simulations. Finally, the effect of dispersing those P3HT/CNT nanocomposites in bulk-heterojunction P3HT-based photovoltaic devices has been evaluated.

The changes induced by exposing multi-walled carbon nanotubes (CNTs) to atomic nitrogen were analysed by high-resolution transmission electron microscopy (HRTEM), x-ray and ultraviolet photoelectron spectroscopy. It was found that the atomic nitrogen generated by a microwave plasma effectively grafts chemical groups onto the CNT surface altering the density of valence electronic states. HRTEM showed that the exposure to atomic nitrogen does not significantly damage the CNT surface.