Ruthenium Nanoparticles Intercalated in Hectorite: A Reusable Hydrogenation Catalyst for Benzene and Toluene

The cationic organometallic aqua complexes formed by hydrolysis of [(C6H6)RuCl2]2 in water, mainly [(C6H6)Ru(H2O)3]2+, intercalate into sodium hectorite by ion exchange, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in ethanol with molecular hydrogen (50 bar, 100°C) with decomposition of the organometallic aqua complexes to give a black material, in which ruthenium(0) nanoparticles (9-18nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. The black ruthenium-modified hectorite efficiently catalyses the hydrogenation of benzene and toluene in ethanol (50 bar H2, 50°C), the turnover frequencies attaining 7000 catalytic cycles per hou

Mechanical properties of electroactive polymer microactuators with ion-implanted electrodes

We report on the use of the bulge test method to characterize the mechanical properties of miniaturized buckling mode dielectric elastomer actuators (DEA). Our actuator consists of a Polydimethylsiloxane (PDMS) membrane bonded to a silicon chip with through holes. Compliant electrodes are fabricated on both sides of the membrane by metal ion implantation. The membrane buckles when a critical voltage is applied to the electrodes. The maximum displacements as well as the efficiency of such actuators strongly depend on the mechanical parameters of the combined electrode-elastomer-electrode layer, mainly effective Young's modulus E and residual stress S. We report measured E and S obtained from bulge tests on PDMS membranes for two PDMS brands and for several different curing methods, which allows tuning the residual stress by controlling the rate of solvent evaporation. Bulge test measurements were then used to study the change in membranes' mechanical properties due to titanium ion implantation, compared to the properties obtained from depositing an 8 nm thick gold electrode. At the doses required to create a conductive layer, we find that the Ti ion implantation has a low impact on the membrane's overall rigidity (doubling of the Young's modulus and reducing the tensile stress) compared to the Au film (400% increase in E). The ion implantation method is an excellent candidate for DEAs' electrodes, which need to be compliant in order to achieve large displacements

Microstructure of 5 keV gold-implanted polydimethylsiloxane

The first high-resolution transmission electron microscopy (TEM) cross-section images of flexible electrodes fabricated by gold ion implantation at 5 keV into polydimethylsiloxane (PDMS) are presented. A TEM sample preparation method based on cryoultramicrotomy, adapted for extremely low-modulus (1 MPa) elastomers, was developed, allowing the gold nanoparticles in a PDMS matrix to be imaged. The cluster size, size distribution and implantation depth of 50 nm were determined from the images and used to calculate the Young’s modulus of the implanted layer

Voltage control of the resonance frequency of dielectric electroactive polymer (DEAP) membranes

We report on the characterization, active tuning and modeling of the first mode resonance frequency of dielectric electroactive polymer (DEAP) membranes. Unlike other resonance frequency tuning techniques, the tuning procedure presented here requires no external actuators or variable elements. Compliant electrodes were sputtered or implanted on both sides of 20 to 35 m thick, 2 to 4 mm diameter polydimethylsiloxane (PDMS) membranes. The electrostatic force from an applied voltage adds compressive stress to the membrane, effectively softening the device and reducing its resonance frequency, in principle to zero at the buckling threshold. A reduction in resonance frequency up to 77% (limited by dielectric breakdown) from the initial value of 1620 Hz was observed at 1800 V for ion-implanted membranes, and a 20% decrease was observed for membranes with sputtered electrodes. Excellent agreement was found between our measurements and an analytical model we developed based on the Rayleigh-Ritz theory. This model is more accurate in the tensile domain than the existing model for thick plates [33] applied to DEAPs. The membranes reported here have resonance frequencies in the audible range. By varying their resonance frequency (and hence their compliance) the membranes can be used as frequency-tunable attenuators. The same technology could also allow the fine-tuning of the resonance frequencies in the MHz range of devices made from much stiffer polymers such as PMMA or SU8.LMT

Mechanical properties of electroactive polymer microactuators with ion-implanted electrodes

Mosquées et centres islamiques : vers l’expansion L’établissement de mosquées et de centres islamiques aux États-Unis remonte au début du xxe siècle. La mosquée la plus ancienne – encore en place aujourd’hui mais transformée en site historique – fut bâtie par des Arabes en 1934 dans l’Iowa. Par la suite, un certain nombre de mosquées et de centres islamiques virent le jour sur l’ensemble du territoire américain. À partir des années 1960 et 1970, durant lesquelles des immigrants qualifiés, sud..

Corrélation entre la forme d'inclusions intergranulaires et l'énergie de joints de grains dans un alliage Cu-1Pb

Le plomb ajouté dans le cuivre et ses alliages est présent aux joints de grains à l'équilibre capillaire sous la forme de lentilles dont la géométrie est gouvernée par leur angle dièdre. Une méthode de mesure de l'angle dièdre permettant d'accéder à une valeur précise pour chaque inclusion a été développée et appliquée aux inclusions individuelles dans un alliage Cu-1Pb. Les résultats obtenus sur une série d'inclusions montrent une grande dispersion à l'échelle d'un échantillon. Cette observation est interprétée comme une conséquence du fait que, pour une température d'équilibration spécifique, l'angle dièdre sur un joint de grains défini dépend de l'énergie de celui-ci. La dispersion constatée sur les valeurs d'angle dièdre obtenues sur un même échantillon peut dès lors être reliée à la dispersion de l'énergie des joints de grains au sein d'un polycristal, laquelle peut à son tour être reliée à la désorientation relative entre les grains, puisque cette dernière est mesurable par analyse EBSD. Le présent article présente des premiers résultats de cette approche

Microactuators based on ion implanted dielectric electroactive polymer (EAP) membranes

We report on the first successfully microfabricated and tested ion-implanted dielectric electroactive polymer (EAP or DEAP) actuators. Dieletric EAP (DEAP) actuators combine exceptionally high energy-density with large amplitude displacements [1,2]. Scaling DEAPs down to the milimeter and micron scale requires patterning compliant electrodes on such a scale on the surfaces of the polymer. We used ion implantation to make the surfaces of the polymer locally conducting. Implanting the compliant electrodes solves the problem of microfabricating patterned electrodes whose elasticity is close to that of the insulating elastomer, thus avoiding the deposition of metal electrodes on the polymer which leads to significant stiffening of the membrane [3]. Several techniques based on ion implantation for chip level and wafer level fabrication are presented. Ion implanted DEAP membranes were both simulated (FEM) and characterized. We report measurements on an actuator consisting of a 30-um-thick ion implanted PDMS membrane bonded to a silicon chip into which a cavity had been etched. We measured 110 um vertical displacements for a 0.72 mm2 square membrane, achieving for the first time the same percent displacement in microscopic EAPs as in macroscopic devices. These observations show that ion implantation allows the patterning of electrodes on PDMS membranes with negligible increase in stiffness

Controlling the lateral aggregation of perfluoroalkylated hexa-peri-hexabenzocoronenes

The investigation of two hexa-peri-hexabenzocoronene (HBC) derivatives carrying linear or branched perfluoroalkylated side chains is reported. Polycondensed aromatic hydrocarbons (PAH) such as HBC derivatives are well known to self-organize to form highly ordered monomolecular stacks, which in turn show a concentration- and solvent-dependent lateral aggregation. However, possible applications of self-assembled HBC derivatives require linear, laterally non-aggregated columnar structures. According to powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC), HBC derivatives with linear perfluoroalkylated side chains show liquid crystalline (LC) properties whereas those with branched perfluoroalkylated side chains have an amorphous structure. The stacking behaviour and the lateral aggregation are found to be greatly influenced by changes in the medium, as shown by fluorescence spectroscopy and cryo-scanning electron microscopy (cryo-SEM)