Pierre Dubot

Adsorption of monoethanolamine on clean, oxidized and hydroxylated aluminium surfaces : a model for amine-cured epoxy/aluminium interfaces

Abstract The interaction of 1-amino-2-hydroxyethane (monoethanolamine) with clean Al(100), in-situ oxidized Al(100) and in-situ hydroxylated Al(100) has been investigated using Auger electron spectroscopy (AES) and high-resolution electron energy-loss spectroscopy (HREELS). It has been shown that, on all these surfaces, adsorption of monoethanolamine can be interpreted in the framework of the Hard and Soft Acid Base (HSAB) principle. However, the detailed mechanism differs for each surface: (i) monoethanolamine interacts with clean Al(100) through its amine termination via a Lewis-like acid-base reaction; (ii) monoethanolamine interacts with oxidized Al(100) through its alcohol termination via a Lewis-like acid-base reaction; (iii) monoethanolamine interacts with hydroxylated Al(100) through its alcohol termination via a Bronsted-like acid-base reaction.

Effects of engineered iron nanoparticles on the bryophyte, Physcomitrella patens (Hedw.) Bruch & Schimp, after foliar exposure

The effects of iron nanoparticles on bryophytes (Physcomitrella patens) were studied following foliar exposure. We used iron nanoparticles (Fe-NP) representative of industrial emissions from the metallurgical industries. After a characterization of iron nanoparticles and the validation of nanoparticle internalization in cells, the effects (cytotoxicity, oxidative stress, lipid peroxidation of membrane) of iron nanoparticles were determined through the axenic culturing of Physcomitrella patens exposed at five different concentrations (5 ng, 50 ng, 500 ng, 5 µg and 50 µg per plant). Following exposure, the plant health, measured as ATP concentrations, was not impacted. Moreover, we studied oxidative stress in three ways: through the measure of reactive oxygen species (ROS) production, through malondialdehyde (MDA) production and also through glutathione regulation. At concentrations tested over a short period, the level of ROS, MDA and glutathione were not significantly disturbed.

HREELS characterization of surfaces and interfaces in self-assembled molecular monolayers

Abstract High resolution electron energy loss spectroscopy ( HREELS ) is used to characterize the extreme surface composition and the interfaces of silane and thiol monolayers deposed on silicon and platinum crystals, respectively. Energy losses due to impact interactions are very sensitive to the molecular groups present in the extreme surface of the film. Long range dipole interactions can supply information about buried interfacial bonds. Silicon substrates were characterized before and after molecular interactions. Energy losses assigned to interfacial siloxane bonds clearly vary with previous substrate annealing. Spectra of adsorbed thiols are dominated by losses corresponding to functional groups attached to the chain-end. An energy loss at 360 cm−1 was identified as corresponding to an interfacial S–Pt bond.

Vibrational spectroscopy of the gas-solid interaction between anhydride molecules and oxide-covered polycrystalline zinc substrate

The room-temperature interaction between anhydride-type molecules and oxide-covered zinc substrates has been studied using infrared reflection-absorption and high-resolution electron energy loss spectroscopies. Gas-solid interactions were carried out extensively for acetic anhydride on polycrystalline zinc substrate, either in-situ prepared, or ex-situ chemically prepared prior to its vacuum introduction. Vibrational spectroscopy revealed the formation of adsorbed carboxylate species in both cases, accompanied by the consumption of surface hydroxyls, which thus appeared to be the active sites in the adsorption process. However, other active surface sites were demonstrated on the ex-situ chemically prepared substrates, namely zinc ions covered by carbonate species which are easily displaced upon anhydride adsorption. The interaction mechanism was found to be the same for the adsorption of maleic and succinic anhydride on industrial zinc-covered substrates.

Structure and surface reactivity of novel nanoporous alumina fillers

Recent studies have shown that the particle size of fillers used for the reinforcement of dental resin composites should be multimodally distributed, in which micron-sized fillers are mixed with nanoparticles so as to achieve a higher filler level in the resin, and should be kept well dispersed so as to be functionalized by a silane. In this study, porous alumina monoliths with high specific surface area, measured by the Brunauer-Emmett-Teller (BET) method, were obtained using a novel preparation method. Structure and surface reactivity have been investigated as functions of temperature and chemical treatments. The impregnation of the as-prepared material by triméthyletoxysilane (TMES) stabilized alumina with high specific surface area at higher temperature. FTIR study has described the effect of TMES treatment and temperature on the structure of the material. The use of allyldimethoxysilane (ADMS), as a probe molecule for measuring the surface reactivity, has allowed us to show that the treatment of samples with TMES and their reheating at 1300 degrees C results in adsorption sites which give stronger chemical bonds. This preliminary study has, therefore, allowed us to optimize the structural and surface treatment of experimental fillers before their use in the reinforcement of resin composites or resin-modified glass ionomer cements.

Investigation of the fivefold icosahedral AlPdMn surface by photoemission and Auger electron spectroscopy

Surface composition and electronic structure of AlPdMn quasicrystalline alloy have been studied for temperature ranging from 300 K to 873 K. The quasicrystalline nature of the in-situ prepared surface was identified by the unusual behaviour of the core level photoemission peaks of Mn as already demonstrated by Thiel et al. Quantitative estimation of surface concentration by measuring the peak on background ratio in Auger electron spectroscopy (AES) do not allow to concluded to surface segregation of one element whatever the substrate temperature. Auger transitions implying valence band electrons in the Auger relaxation reveal interesting shapes and energies modifications that can be correlated with the typical electronic structure of this alloy. The appearance of strong satellite structure in the Auger and photoemission spectrum can be attributed to bulk plasmon of the quasicrystalline phase.

Two steps bulk-surface functionalization of nanoporous alumina by methyl and vinyl-silane adsorption. Evidence for oxide surface highly reactive sites creation.

Functionalization of a novel nanoporous monolithic alumina synthesized from amalgam is investigated. The structure is studied by X-ray diffraction, BET, MEB and IR spectroscopy, before and after chemical functionalization by trimethylethoxy silane adsorption and annealing at high temperature. These treatments retain both monolith microstructure and nanostructure while strongly improving material mechanical properties. Allyldimethoxysilane and alcohol adsorption on the annealed samples, proves that highly reactive sites are available for further polymer grafting, as demonstrated by a significant shift of allyldimethoxysilane νSiH to 2,215xa0cm−1 and adsorbed acetate formation. Simple quantum computations on model systems support this conclusion. Chemical processes reported in this paper, allow a nanostructured alumina monoliths functionalization to optimize ceramics-polymer bonds, and to tune new hybrid biomaterial properties.