Caractérisation des propriétés mécaniques de vernis photopolymères par micro-indentation et simulation par éléments finis.

Afin de caractériser les propriétés mécaniques de vernis photopolymérisés d’épaisseurs 15 et 80 µm, des essais par Analyse Mécanique Dynamique (D.M.A.) et par micro-indentation ont été menés. Les résultats expérimentaux sont confrontés au moyen de simulations par éléments finis (Abaqus). Un premier modèle viscoélastique a permis de simuler correctement la charge et le plateau de fluage, mais s’avère insuffisant pour simuler la décharge

Photoinduced hydrosilylation through hydrogen abstraction: an NMR and computational study of the structural effect of silane

The hydrosilylation reaction, describing the addition of Si–H bonds to unsaturated bonds, is performed in the presence of catalysts, usually highly active platinum catalysts. This work focuses on the study of a photoinduced hydrosilylation by the use of benzophenone which promotes the addition reaction of olefin on different hydrosilanes. The reactivity of silanes towards addition onto the double bond during hydrosilylation appears to depend on their structure. It was observed that the consumption of Si–H and C[double bond, length as m-dash]C functional groups increases with the irradiation time, and reaches a maximum of approx. 51% in the case of diphenylsilane. The hydrosilylation products are determined with (1)H NMR, HSQC, DEPT, COSY and (13)C NMR. The main product corresponds to the single adduct of the silyl radical onto the double bond. Substitution of the Si–H bond by two or three phenyls groups (triphenylsilane, diphenysilane) enhances the yield of the reaction, although diphenylsilane was found to be more efficient than triphenylsilane because of its lower steric hindrance. The ketyl radical formed after hydrogen abstraction by the triplet state of benzophenone likely forms benzopinacol, a reaction which reduces the overall yield of the hydrosilylation reaction. All these experiments are in line with DFT calculations of the Gibbs free energy of the reactions involved. This sheds new light on the photoinduced hydrosilylation process and opens the way to more active combinations of photoinitiator/silane/vinylsilane systems

Direct-to-metal UV-cured hybrid coating for the corrosion protection of aircraft aluminium alloy

Finding eco-efficient and environmentally viable alternatives to chromate coatings represents a fundamental milestone in the aerospace industry. Here, we show a chromate-free approach to protective hybrid coatings on aluminium alloy (AA2024-T3) departing from photoinduced sol–gel and cationic polymerizations. Beginning with a film of n-alkyltrimethoxysilane and diepoxy monomer, we rely on photogenerated superacids to induce the single step formation of two inorganic and organic barrier networks. Such system combines the unique aspects of photopolymerization including fast reactions, temporal control, solvent-free composition and temperature independence. Used without chemical conversion coating or anodizing, some films have passed 2000h of salt spray testing

Fabrication of copper objects through lithography-based metal manufacturing

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On-Demand Photopolymerization of Fiber-Reinforced Polymers Exhibiting the Shape Memory Effect

Fiber-reinforced polymers exhibiting the shape memory effect were created on the basis of a one-pot three-step chemical process. The first step is a Michael addition, which creates linear polymer chains. The second step is free radical photopolymerization, which increases the degree of curing of polymers. The last step is post-consolidation due to the reaction of previously formed secondary amines on the residual double bonds. By employing such chemistry to impregnate glass fibers, the final composite exhibits a convincing shape memory effect, as shown by cyclic thermomechanical tests

Y-TZP, Ce-TZP and as-synthesized Ce-TZP/Al2O3 materials in the development of high loading rate digital light processing formulations

International audienceY-TZP, Ce-TZP and Ce-TZP/Al2O3 materials are widely investigated in dentistry. Digital Light Processing (DLP) is considered as a breakthrough technology for the dental field to fine print Y-TZP green parts. High loading photocurable formulations (>45 vol%) with Y-TZP , Ce-TZP commercial powders and Ce-TZP/30vol% Al2O3 as-synthesized powder suitable to DLP printing were achieved in this study. A low specific surface area (5-13 m²/g) of particles without any pores and 1 wt% to 2 wt% of steric dispersant are required to obtain high loading formulations. The as-synthesized composites provide these properties by increasing the calcination temperature from 800°C to 1200°C. The as-prepared ceramic formulations based on the same photocurable resin exhibit a curing behavior suitable to DLP process for Y-TZPformulations (thickness > 50 μm in few seconds with a high conversion rate) in comparisonwith ceria ceramic. The ceria is a strongly UV absorbing material and a specific formulationis developed to obtain 80% of conversion and a cured thickness of 75 μm in 0.5 s

UV powder coatings containing synthetic Ag-beidellite for antibacterial properties

International audienceThe preparation of antibacterial UV powder coatings dedicated to wood based panels is described in the present study. Two experimental methods were investigated: the generation of silver nanoparticles during the polymerization of UV powders and the introduction of a silver modified beidellite within UV powder formulations. While the first method leads to some nanoparticle aggregation, this phenomenon was avoided with the second approach. Antibacterial activity was thus ensured by the presence of beidellite modified with silver cations. XRD, X-ray fluorescence, SEM/EDX and TEM analyses allowed a complete characterization of the Ag-beidellite before its incorporation within UV powder formulations. Real-time-FTIR spectroscopy fitted with an environmental cell was used to monitor the reactivity of UV powder formulations under UV light and temperature control. Resulting coatings were finally characterized by UV spectroscopy, DMA in tension mode, XRD, TEM and antimicrobial analyses. It was shown that the fully cured and homogeneous coatings exhibit high thermomechanical properties and antibacterial activity

Assessing Mesoscopic Organization in Copolymer-Templated Silica Hybrid Films via Solid-State Nuclear Magnetic Resonance

International audienceIn the context of increasing use of nanostructured materials, finding innovative characterization methods able to assess precisely the level of ordering is essential. To this end, a range of model organic-inorganic copolymer-silica films is synthesized using poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) amphiphilic triblock copolymer as supramolecular template. Upon increasing copolymer concentration (10-100 wt%), the order can be gradually enhanced from short-range to long-range as proved by conventional techniques such as X-ray diffraction and electron microscopy. To evaluate the level of mesoscopic organization, the same series of samples is also analyzed by solid-state NMR spectroscopy. The disorder-to-order transition is probed by 1 H and 13 C magic angle spinning nuclear magnetic resonance (NMR) spectra through the increase in chemical environment uniformity and chain mobility respectively, which both result from the self-assembly mechanism. 1 H NMR relaxation measurements (T2) using low-field NMR spectroscopy are instrumental to identify the threshold template concentration where ordering takes place

Surfactant-directed synthesis of mesoporous films made single-step by a tandem photosol-gel/photocalcination route

In view of their technological impact in materials chemistry, a simplified and more efficient synthetic route to mesoporous films is highly sought. We report, herein, a smart UV-mediated approach coupling in a one-stage process sol-gel photopolymerization and photoinduced template decomposition/ablation to making mesoporous silica films. Performed at room temperature with a solvent-free solution of silicate precursor and amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer, the synthesis relies on photoacid generation to induce the fast formation (≈10 min) of mesostructured silica/surfactant domains. Continuation of UV exposure for three additional hours enables subsequent and complete photodegradation of the polyether copolymer, resulting in ordered or disordered mesoporous silica film. One of the most attractive features is that the one-step procedure relies on a continuous illumination provided by the same conventional medium-pressure Hg-Xe arc lamp equipped with a 254 nm reflector to enhance the emission of energetic photons <300 nm. In addition to X-ray diffraction and transmission electron microscopy, time-resolved Fourier transform infrared spectroscopy has proved to be a powerful in situ technique to probe the different chemical transformations accompanying irradiation. Photocalcination strengthens the inorganic network, while allowing to preserve a higher fraction of residual silanol groups compared with thermal calcination. A polyether chain degradation mechanism based on oxygen reactive species-mediated photo-oxidation is proposed