Edmond Payen

Adhesion enhancement by a dielectric barrier discharge of PDMS used for flexible and stretchable electronics

Currently, there is a strong tendency to replace rigid electronic assemblies by mechanically flexible and stretchable equivalents. This emerging technology can be applied for biomedical electronics, such as implantable devices and electronics on skin. In the first step of the production process of stretchable electronics, electronic interconnections and components are encapsulated into a thin layer of polydimethylsiloxane (PDMS). Afterwards, the electronic structures are completely embedded by placing another PDMS layer on top. It is very important that the metals inside the electronic circuit do not leak out in order to obtain a highly biocompatible system. Therefore, an excellent adhesion between the 2 PDMS layers is of great importance. However, PDMS has a very low surface energy, resulting in poor adhesion properties. Therefore, in this paper, PDMS films are plasma treated with a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0 kPa). Contact angle and XPS measurements reveal that plasma treatment increases the hydrophilicity of the PDMS films due to the incorporation of silanol groups at the expense of methyl groups. T-peel tests show that plasma treatment rapidly imparts adhesion enhancement, but only when both PDMS layers are plasma treated. Results also reveal that it is very important to bond the plasma-treated PDMS films immediately after treatment. In this case, an excellent adhesion is maintained several days after treatment. The ageing behaviour of the plasma-treated PDMS films is also studied in detail: contact angle measurements show that the contact angle increases during storage in air and angle-resolved XPS reveals that this hydrophobic recovery is due to the migration of low molar mass PDMS species to the surface.

Parallel between infrared characterisation and ab initio calculations of CO adsorption on sulphided Mo catalysts

Abstract Carbon monoxide adsorption on sulphided Mo catalysts has been investigated by means of IR spectroscopy and DFT ab initio calculations. IR experiments show that CO adsorption on the sulphide phase of Mo/Al2O3 catalysts gives rise to various ν(CO) bands, the intensities of which are strongly modified when post-treatment of the catalyst with H2 or H2S is performed before CO adsorption, therefore, revealing strong modifications in the nature and the number of sites present on the sulphide phase. Ab initio periodic DFT calculations allow to define two types of edges for MoS2, which sulphur coverage and structure depend on the H2/H2S ratio in the surrounding atmosphere. Adsorption energies and stretching wavenumber of CO adsorbed on the various sites of these surfaces were computed, providing the possibility to compare for the first time results from theoretical calculations and spectroscopic measurements on these systems. A novel attribution of the main IR features of CO adsorbed on MoS2 is proposed.

New generation of titanium dioxide support for hydrodesulfurization

Mesoporous titanium oxide with a high specific surface area of 120 m 2 /g prepared by a novel method developed by Chiyoda was used for supporting molybdenum sulfide. In order to examine the influence of the surface area on the properties of the molybdenum sulfide phase, two different samples of titanium oxide were studied, a commercial one with a surface area of 72 m 2 /g and that prepared by Chiyoda. Molybdenum was deposited on the TiO2 supports by incipient wetness impregnation with ammonium heptamolybdate in one or two steps depending on the Mo loading. Some samples were also prepared by impregnation of ammonium heptamolybdate basified by ammonia. Raman spectroscopy and XPS were used to examine the nature of the molybdate phase and its dispersion in the oxidic state. HREM and XPS were used for studying the sulfided state. As expected, the maximum amount of well-dispersed molybdenum is higher on the Chiyoda support than on the reference support with a lower surface area. The catalytic properties of the catalysts were studied in dibenzothiophene conversion. For the Chiyoda support, the catalytic activity varied linearly with the Mo loading up to 6–7 Mo/nm 2 then became nearly constant for the higher loadings. Much higher activities (six times, expressed per gram of catalyst) were obtained compared to molybdenum sulfide supported on alumina.

Modification of structural and acidic properties of sol–gel-prepared alumina powders by changing the hydrolysis ratio

The structural and acidic properties of sol–gel prepared alumina powders as catalyst supports were modified by adjusting the hydrolysis ratio, R (i.e. molar ratio of water relative to the alumina precursor, R=[H2O]/[aluminium-tri-sec-butoxide (ASB)]). Structural properties (e.g. porosity) and acidic properties were measured for alumina powders prepared with various R values, from 3 to 13. For R 10, first-order particles were closely packed with ink-bottle-type pore structures, whereas for R=9 or 10, first-order particles were loosely packed with a spatial fractal arrangement that yielded pseudo-cylindrical pore structures. In addition, the alumina powders prepared with R=9 or 10 had larger water pore volume and stronger acidity than those with other R values. These properties unique to the powders prepared with R=9 or 10 were ascribed to relatively short Al–O–Al chain lengths that resulted in loose packing of first-order particles. The results here indicate that alumina powders with favorable properties as catalyst supports (e.g. mean pore diameter) can be tailored by selecting the appropriate R in the sol–gel synthesis process.

The existence and stability of the silica-supported 12-molybdophosphoric acid keggin unit as shown by Raman, XPS, and 31P NMR spectroscopic studies

Abstract Silica-supported 12-molybodophosphoric acid catalysts developed for partial oxidation of methane have been characterized by laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy, and 31 P NMR spectroscopy after preparation, calcination, and use in catalytic tests performed at high-temperature (570°C) and atmospheric pressure, It is shown that the 12-molybdophosphoric acid (HPMo) Keggin unit (KU) can be deposited uniformly on the silica surface in a highly dispersed form up to a coverage of 0.04 KU nm −2 . Aggregates are then formed for loading up to about 0.12 KU nm −2 . At higher loading these aggregates are likely to grow to give particles of 12-molybdophosphoric acid. Both LRS and 31 P NMR spectroscopic results demonstrate that the highly dispersed HPMo is stable up to calcination or reaction temperatures of about 580–600°C. On the contrary, the particles of HPMo present on the highly loaded catalysts disappear after catalytic testing to give M003 as shown by LRS. The increase in stability of the supported HPMo KU compared with that of bulk HPMo is proposed to be the result of the interaction of the KU with some surface site of the silica, giving the highly dispersed and dehydrated HPMo species thought to be responsible for the catalytic activity for methane partial oxidation.

A simple and reproducible method for the synthesis of silica-supported rhodium nanoparticles and their investigation in the hydrogenation of aromatic compounds

Colloidal suspensions of rhodium nanoparticles have been easily prepared in aqueous solution by chemical reduction of the precursor RhCl3·3H2O in the presence of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (HEA16Cl) and further used to immobilize rhodium nanoparticles on silica by simple impregnation. The obtained silica-supported rhodium nanoparticles have been investigated by adapted characterization methods such as transmission electron microscopy and X-ray photoelectron spectroscopy. A particle size increase from 2.4 to 5 nm after the silica immobilization step and total elimination of the surfactant has been observed. This “heterogeneous” catalyst displayed good activities for the hydrogenation of mono-, di- alkylsubstituted and/or functionalized aromatic derivatives in water under atmospheric hydrogen pressure and at room temperature. In all cases, the catalyst could be recovered several times after a simple decantation or filtration and reused without any significant loss in catalytic activity. This supported catalyst has also been tested under higher hydrogen pressure giving rise to TOFs reaching 6430 h−1 at 30 bar and in terms of catalytic lifetime 30 000 TTO in 8.5 h for pure anisole hydrogenation at 40 bar.

Raman spectroscopic evidence for the existence of 6-molybdoaluminate entities on an Mo/Al2O3 oxidic precursor

A study by Raman spectroscopy of the oxomolybdate surface phase present on an Mo/Al2O3 oxidic precursor reveals the presence of well dispersed 6-molybdoaluminate entities (AlMo6O24H63-) on a 15 wt.% MoO3 oxidic precursor. It is also shown that precipitation of an ammonium 6-molybdoaluminate salt occurs at higher Mo loadings.

Alumina supported HDS catalysts prepared by impregnation with new heteropolycompounds. Comparison with catalysts prepared by conventional Co–Mo–P coimpregnation

Abstract Hydrodesulfurization (HDS) catalysts prepared by the incipient wetness impregnation method with Co–Mo–P based solutions were characterized with various physical techniques and their efficiencies in HDS of thiophene were evaluated. Depending on the Co–Mo–P precursors used to prepare the impregnating solution, different heteropolyanions (HPAs) were characterized. In conventional solutions, P2Mo5O6−23 or P2Mo18O6−62 type entities were evidenced. Preparations with Keggin type HPAs were also studied (PMo12O3−40) and an original method of preparation which allows the deposition of alumina on reduced Keggin type HPAs (PMo12O7−40) is described. If the non-reduced HPAs (whatever their structure) are decomposed on alumina, the reduced ones could be partially preserved even after calcination, leading to the synthesis of more efficient catalysts.

Surface Modification of Non-woven Textiles using a Dielectric Barrier Discharge Operating in Air, Helium and Argon at Medium Pressure

In this paper, polyethylene terephthalate (PET) and polypropylene (PP) non-wovens were modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The helium and argon discharges contained a fraction of air smaller than 0.1 %. Surface analysis and characterization were performed using X-ray photoelectron spectroscopy, liquid absorptive capacity measurements and scanning electron microscopy (SEM). The non-wovens, modified in air, helium and argon, showed a significant increase in liquid absorptive capacity due to the incorporation of oxygen-containing groups, such as C—O, O—C=O and C=O. It was shown that an air plasma was more efficient in incorporating oxygen functionalities than an argon plasma, which was more efficient than a helium plasma. SEM pictures of the plasma-treated nonwovens showed that the hydrophilicity of the nonwovens could be increased to a saturation value without causing physical degradation of the surface. The ageing behavior of the plasma-treated textiles after storage in air was also studied. It was shown that during the ageing process, the induced oxygen-containing groups re-orientated into the bulk of the material. This ageing effect was the smallest for the argon-plasma treated non-wovens, followed by the helium-plasma treated non-wovens, while the air-plasma treated non-wovens showed the largest ageing effect.

Industrial MoO3-promoter oxide-γ-Al2O3 hydrotreating catalysts: genesis and architecture description

Abstract The catalytic performances (activity, selectivity, deactivation by phase transformation …) of hydrotreating catalysts composed of supported Mo associated with a promoter (Co or Ni) and working in a sulphided state are greatly dependent on the sequences and conditions of the preparation process. A large number of works dealing with the description of one or several steps in the catalyst elaboration have been already published, specially in the previous Molybdenum Conference in which review articles can be found. However, in these works, all the preparations sequences are not always considered and some experimental conditions are far from those used in industrial catalyst preparation in the oxide or commercial form. In this paper we report new results about the architecture of oxide precursors of series of Mo-based catalysts prepared according to industrial conditions. These results will be compared and discussed with other descriptions already published. Starting with the support and commercial products chosen because they are very soluble in water, easily decomposed and less expensive [ammonium heptamolybdate (AHM), and cobalt or nickel nitrate], six steps, viz. molybdate impregnation, intermediate drying and calcination, impregnation of the promoter solution, drying and final calcination, are necessary to obtain the final or commercial catalyst. Moreover after the intermediate or final calcination, the samples prepared can be modified by aging during storage in the laboratory atmosphere. The nature and quantity of the supported species, their structure and size, the chemical state of the elements, their dispersion on the support, the interaction between the molybdate entities, with the support or with the promoter, are among the main aspects, considered in this investigation for which we used techniques dealing with surface characterization X-ray photoelectron spectroscopy (XPS) and ion-scattering spectroscopy (ISS)] and a vibrational technique such as laser Raman spectroscopy (LRS). During the first impregnantion step, an electrostatic interaction between the ionized surface species of the support and the molybdate ions in solution occurs. The subsequent drying and calcination steps induce formation of strong chemical bonds between the supported molybdate species and the carrier. After this step, the species are well dispersed on the support as proved by XPS and ISS. The second impregnation transforms the molecular aggregates previously created by (partial) hydrolysis and therefore gives back the initial species. The added promoter is then interacting with the polymolybdate or the support. Calcination can provoke a partial incorporation of the promoter into the support but bilayers in which the promoter is between the molybdate phase and the support are not detected. Aging of the catalyst after the calcination step is a hydration process. Reverse dehydration can be achieved by a new calcination step.