Étude de la formation de couches organiques auto assemblées à l'aide de la spectroscopie d'impédance électrochimique "odd random phase multisine"

L'objectif de ce travail est d'observer la croissance de couches organiques formées à partir d'acide phosphonique sur un substrat aluminium. Pour ce faire, nous avons utilisé la technique d'impédance électrochimique dite "odd random phase multisine" spécifique au laboratoire. La particularité de cette technique est la possibilité d'évaluer le bruit stochastique, la non stationnarité et la non linéarité du système lors de la mesure du spectre d'impédance. De plus, le temps de mesure est fortement réduit. Des mesures d'impédance ont été réalisées toutes les 10 minutes lors de la formation de la couche. L'analyse des erreurs a permis de faciliter l'ajustement des diagrammes à l'aide d'un schéma électrique équivalent. Les résultats de cet ajustement montrent que la technique est bien adaptée pour suivre l'évolution de la formation de la couche

Nanostructured organic radical cathodes from self-assembled nitroxide-containing block copolymer thin films

This contribution describes the formation of nanostructured thin film organic radical cathodes. First, the self-assembly of poly(styrene)-block-poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA-b-PS) diblock copolymers is detailed. In order to improve the nano-morphology of the immiscible PTMA and PS domains, the effect of thermal and solvent annealing is investigated. The formation of thin films with different morphologies such as cylindrical or lamellar nanostructures is observed depending on the processing conditions. The electrochemical properties of the nanostructured films are further investigated to assess the redox activity of the PTMA domains. Cyclic voltammetry of PTMA-b-PS diblock copolymers, either in dissolved or thin film supported configuration, confirms the reversible redox behavior of the nitroxide radical. Galvanostatic cycling of the thin film nanostructured cathodes reveals good capacity retention with fast charge/discharge response resulting from efficient charge and ion transfer as well as structural integrity. Such nanostructured organic radical cathodes provide opportunities for the fabrication of new generation nanostructured organic radical battery architectures

Ion yield enhancement at the organic/inorganic interface in SIMS analysis using Ar-GCIB

Argon gas cluster ion beams (Ar-GCIBs) provide new opportunities for molecular depth profiling and imaging of organic materials and biological samples, thanks to recent technological developments that have led to the construction of new SIMS spectrometers where the traditional issues related to their low lateral resolution along with poor mass resolution and mass accuracy are overcome. The present fundamental contribution on SIMS molecular depth profiling investigates the variations of the secondary ion signals observed at the organic–inorganic hybrid interface when using Ar-GCIB as the analytical beam. With this in mind, depth profiling experiments were performed with a ToF-SIMS spectrometer using different analysis beams: 30-keV Bi5+ versus 10-keV Arn+ with a cluster size (n) of 800, 1500, 3000 and 5000 atoms, respectively. A 10-keV Ar3000+ beam was used for sputtering in all the experiments. Irganox 1010 and model polymers such as polystyrene (PS) and poly (methyl methacrylate) (PMMA) oligomers were chosen. Silicon wafer and a polymer-based substrates were employed to test materials with different stiffness, which is directly related to their Young’s moduli, an important parameter in this study. Ar-GCIB depth profiles systematically show ion signal enhancement of the characteristic fragments of PS and Irganox 1010 when approaching the interface with the silicon substrate, that can reach up to 60% for [M1010-H]− in Irganox films deposited onto silicon wafers. This enhancement increases with increasing n in both ion polarities. These results point out some ionization effects on the observed signal enhancement at the interface. The experimental observations will be explained on the basis of the physics of the impact of large argon clusters on different target materials and the energy confinement of the ion projectile in the organic overlayers. Finally, the thickness of organic films on rigid substrates in the nanoscale appears to be a crucial parameter to dramatically improve the sensitivity to molecular fragments when using large Ar cluster ions as analysis beams

Effect of microstructural defects on passive layer properties of interstitial free (IF) ferritic steels in alkaline environment

The role of microstructural defects (dislocation density and grain boundary areas) on the passive film properties formed on cold- and hot-rolled interstitial free (IF) steels is investigated in 0.1 M NaOH solution. Electron backscattered diffraction (EBSD) shows higher microstructural defect density on cold-rolled samples. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) results exhibit the lower barrier properties of passive films with the increase in microstructural defects. This is attributed to the increase in donor density measured with Mott-Schottky analysis and the lower relative quantity of protective γ-Fe2O3 in passive films (composed of Fe3O4,γ-Fe2O3 and FeO(OH)) with the increase in microstructural defect density.</p

Controlling and Probing the Nano Interaction Between Organic Molecules and Al Alloys

Materials Science and EngineeringMechanical, Maritime and Materials Engineerin

Comprehensive study of the macropore and mesopore size distributions in polymer monoliths using complementary physical characterization techniques and liquid chromatography

Poly(styrene‐co‐divinylbenzene) monolithic stationary phases with two different domain sizes were synthesized by a thermally initiated free‐radical copolymerization in capillary columns. The morphology was investigated at the meso‐ and macroscopic level using complementary physical characterization techniques aiming at better understanding the effect of column structure on separation performance. Varying the porogenic solvent ratio yielded materials with a mode pore size of 200 nm and 1.5 μm, respectively. Subsequently, nano‐liquid chromatography experiments were performed on 200 μm id × 200 mm columns using unretained markers, linking structure inhomogeneity to eddy dispersion. Although small‐domain‐size monoliths feature a relatively narrow macropore‐size distribution, their homogeneity is compromised by the presence of a small number of large macropores, which induces a significant eddy‐dispersion contribution to band broadening. The small‐domain size monolith also has a relatively steep mass‐transfer term, compared to a monolith containing larger globules and macropores. Structural inhomogeneity was also studied at the mesoscopic level using gas‐adsorption techniques combined with the non‐local‐density‐function‐theory. This model allows to accurately determine the mesopore properties in the dry state. The styrene‐based monolith with small domain size has a distinctive trimodal mesopore distribution with pores of 5, 15, and 25 nm, whereas the monolith with larger feature sizes only contains mesopores around 5 nm in size

Compositional Study of a Corrosion Protective Layer formed by Leachable Lithium Salts in a Coating Defect on AA2024-T3 Aluminium Alloys

Organic primer coatings loaded with environmentally harmful Cr(VI) corrosion inhibitive pigments still play an important role in corrosion protection of aluminium alloys for the aerospace industry. A potential green alternative coating system has recently been developed, loaded with lithium salt corrosion inhibitors. Under exposure to neutral salt spray, lithium salts leach from the organic coating into coating defects to induce the formation of a corrosion protective layer. In this work the composition and growth of this protective layer is investigated by time-of- ight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS imaging is successfully applied to monitor the lateral spread of leaching lithium salts in artificial one-millimeter-wide scribes. The chemical composition of the protective layer is revealed by comparing the mass spectra of salt spray exposed scribe areas to the mass spectra of pseudoboehmite and aluminium-lithium layered double hydroxide reference samples. The insights obtained in this work have led to a thorough understanding of the formation mechanism of the protective layer and provide local chemical and structural information which can be linked to corrosion protection behavior

Compositional Study of a Corrosion Protective Layer formed by Leachable Lithium Salts in a Coating Defect on AA2024-T3 Aluminium Alloys

Organic primer coatings loaded with environmentally harmful Cr(VI) corrosion inhibitive pigments still play an important role in corrosion protection of aluminium alloys for the aerospace industry. A potential green alternative coating system has recently been developed, loaded with lithium salt corrosion inhibitors. Under exposure to neutral salt spray, lithium salts leach from the organic coating into coating defects to induce the formation of a corrosion protective layer. In this work the composition and growth of this protective layer is investigated by time-of- ight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS imaging is successfully applied to monitor the lateral spread of leaching lithium salts in artificial one-millimeter-wide scribes. The chemical composition of the protective layer is revealed by comparing the mass spectra of salt spray exposed scribe areas to the mass spectra of pseudoboehmite and aluminium-lithium layered double hydroxide reference samples. The insights obtained in this work have led to a thorough understanding of the formation mechanism of the protective layer and provide local chemical and structural information which can be linked to corrosion protection behavior

Adhesive bonding and corrosion performance investigated as a function of auminum oide chemistry and adhesives

The long-term strength and durability of an adhesive bond is dependent on the stability of the oxide-adhesive interface. As such, changes in the chemistry of the oxide and/or the adhesive are expected to modify the interfacial properties and affect the joint performance in practice. The upcoming transition to Cr(VI)-free surface pretreatments makes it crucial to evaluate how the incorporation of electrolyte-derived sulfate and phosphate anions from, respectively, phosphoric acid anodizing and sulfuric acid anodizing affect the interfacial chemical properties. Hence, different types of featureless aluminum oxides with well-defined surface chemistries were prepared in this study. The relative amounts of O2−, OH−, , and surface species were quantified using x-ray photoelectron spectroscopy. Next, bonding with two types of commercial aerospace adhesive films was assessed by peel and bondline corrosion tests. The presented results indicate that the durability of the oxide-adhesive interface depends on the interplay between oxide and adhesive chemistries. Epoxy adhesion is highly affected by changes in the oxide surface chemistry, especially the amount of surface hydroxyls. However, the performance of anodic oxides with a lower hydroxyl fraction can be significantly enhanced by the presence of covalent bonds using a silane coupling agent, γ-amino propyl triethoxy. On the contrary, results with Redux 775 adhesive exhibit very low sensitivity to variations in the surface chemistry. Bondline corrosion resistance of the joints is mainly determined by the nature of the adhesive, independent of the varying oxide chemistries.Accepted Author Manuscript(OLD) MSE-6(OLD) MSE-