Search

International audience; The dynamics of plaster drying and the impact of subflorescence on the process are described through Magnetic Resonance Imaging and X-Ray Microtomography measurements. It is shown that crystals deposit around the air-liquid interface the closest to the sample free surface, which induces a recession of this interface within the sample at a rate only depending on the current saturation (water to pore volume ratio). Thus the distribution of crystals deposited during evaporation essentially depends on the history of saturation. The drying dynamics then results from vapor diffusion through the less porous layers of crystal accumulation below the sample free surface. This in particular makes it possible to predict the dramatic decrease of the drying rate after successive imbibition-drying cycles.

Structural properties of aqueous Na-silicates at both room and high temperature (below 500°C) have been investigated to better understand the microscopic evolution of structure and the macroscopic phenomenon of foaming. NMR spectroscopy has provided a direct quantification of structural units defined as Qn. Solid-state NMR along with Raman spectroscopy has indicated the extent of local structural reorganization on heating the silicates. Heating an aqueous Na-silicate leads to structural changes due to the removal of water, where the quantity of leftover water in the system obeys an Arrhenian evolution with an activation energy of 30 kJ.mol−1. TGA, NMR and Raman measurements suggest that the structure becomes similar to the one of hydrated silicate glasses studied in geochemistry. Increasing the Na concentration results in a larger quantity of water retained after a pre-drying treatment, which correlates with a lower softening temperature of the material and is, macroscopically, related to foaming of the silicate.

International audience; β-anhydrite, the stable form of CaSO4, is a common mineral and a key phase in gypsum's dehydration mechanism. An in-depth multi-scale investigation of its structure by powder X-ray diffraction revealed a very slight distortion of the crystal cell at room temperature (β = 90.092(9) °), that led to rule out the commonly admitted orthorhombic model (space group Cmcm) in favor of monoclinic C2/c subgroup. According to high-temperature XRD, the structure resumes however the orthorhombic symmetry around 400 °C.

International audience; When laminated glass shatters under impact, most of the energy dissipation occurs in the coupled delamination and stretching of the polymer interlayer between broken chunks of glass. The strong dependency of these mechanisms on interlayer nature, on loading rate and on temperature has been previously investigated: however, the effect of the interfacial adhesion is unexplored. In this work, a surface modification technique is proposed, along with a mechanical characterization of the debonding with the Through Crack Tensile Test. We show that while increasing adhesion has the effect of enhancing the energy required to propagate the delamination fronts as well as the stretch level of the delaminated interlayer, the dissipation associated to the stretching of the volume of the PVB interlayer seems unaffected. We attribute this effect to the competition between the changes in both stretch and stretch rate in the viscoelastic interlayer. Finally, we discuss the experimental observation of the limits of the steady-state debonding regime, related to the competition between adhesive crack propagation and cohesive failure in the interlayer.

International audience; The impact of polypropylene and high-density polyethylene backbone binders on the structure of organic matrix, feedstock, and ceramic parts is investigated in terms of morphology in this paper. The miscibility of wax with polyethylene and polypropylene is investigated in the molten state via a rheological study, revealing wax full miscibility with high-density polyethylene and restricted miscibility with polypropylene. Mercury porosimetry measurements realized after wax extraction allow the characterization of wax dispersion in both neat organic blends and zirconia filled feedstocks. Miscibility differences in the molten state highly impact wax dispersion in backbone polymers after cooling: wax is preferentially located in polyethylene phase, while it is easily segregated from polypropylene phase, leading to the creation of large cracks during solvent debinding. The use of a polyethylene/polypropylene ratio higher than 70/30 hinders wax segregation and favors its homogeneous dispersion in organic binder. As zirconia is added to organic blends containing polyethylene, polypropylene, and wax, the pore size distribution created by wax extraction is shifted towards smaller pores. Above zirconia percolation at 40 vol%, the pore size distribution becomes sharp attesting of wax homogeneous dispersion. As the PP content in the organic binder decreases from 100% to 0%, the pore size distribution is reduced of 30%, leading to higher densification ability. In order to ensure a maximal densification of the final ceramic, polyethylene/polypropylene ratios with a minimum content of 70% of high-density polyethylene should be employed.

International audience; This article presents a simple thermal characterization method, noted CFM, for the measurement of the apparent thermal conductivity of insulating materials at high temperature (i.e., up to 600°C). The CFM method is a steady-state relative measurement method which requires a calibration. The calibration of the experimental apparatus was done with a calcium silicate board of known thermal conductivity. Thermal conductivity measurements were carried out on a low-density compressible fibrous felt and a high-density calcium silicate board between 100 and 600°C. A good agreement was observed with the values obtained with the guarded hot-plate (GHP) method for the low-density fibrous felt and the parallel hot-wire (PHW) method for the high-density calcium silicate board. The measurement of the apparent thermal conductivities of low-density fibrous felts of different apparent densities, combined with a simple conducto-radiative model, allowed to estimate a mean specific extinction coefficient in good agreement with a value derived from transmittance/reflectance measurements. Keywords Insulating material. High temperature. Thermal conductivity 1 Introduction Knowledge of the thermal conductivity of insulating materials at high temperature is of great importance for the control of industrial processes. For example, the cooling rate of a liquid metal in a mold (which has a great influence on the mechanical properties of the molding) is highly dependent on the thermal resistance of the surrounding insulation. Thermal insulation materials are usually porous materials. Their thermal transport properties, at a macroscopic scale, are not intrinsic values since they depend on the local structure of the material (i.e., porosity, tortuosity) [1] and the contributions of several heat transfer modes (i.e., conduction, convection and/or radiation). The term apparent (or effective) thermal conductivity is thus used for porous materials. The characterization of the thermal transport properties (i.e., thermal conductivity and thermal diffusivity) of materials can be performed with a large variety of methods. The choice of the method depends on the following criteria: the nature of the material, the size and shape of the specimen, the temperature range, the thermal conductivity and thermal diffusivity range, the uncertainty of measurement [2].

International audience; The performances of Pressure Sensitive Adhesives (PSA) are generally evaluated using different loading geometries such as tack, peel and shear tests. It is difficult to link the behaviors of PSAs in these different geometries, and to predict the result of one test from another, because the confinement of a soft and dissipative material prevents the use of standard fracture mechanics, which separates the interface debonding behavior from the dissipation associated with the bulk deformation. We present here an original experimental investigation based on the modeling strategy proposed by Creton and Ciccotti[1]. Using instrumented versions of both peel and tack measurements, we compared the adherence performances of a series of model PSAs based on styrene-isoprene block copolymers, while identifying the mesoscale mechanisms at play during debonding. This analysis method allows us to model the contribution of the large strain rheology of the PSAs in the total work of debonding. We clearly show that both the adherence performances and local mechanisms can be closely related between peel and tack when considering both similar confinement and a similar strain rate of the fibrils that are spontaneously formed during debonding. While the overall adherence properties change by a factor of 3 between the different samples, the peel tests only present a minor +20% bias in adherence, which can be attributed to the combination of a 10% increase in the average stress and a 10% increase in the maximum strain of the fibrils. This improvement in the understanding of the PSA performances opens the way to a more sound mechanical design of PSA based joints.

International audience; Lightweight plasterboard is a product composed of plaster foam core whose porosity can reach 75 vol%, lined with two sheets of paper. To optimize the trade-o between thermal resistance and mechanical strength, it is important to understand and characterize the mechanical behavior of plasterboard. Core compaction of plasterboard is one of the prevalent degradation mechanism. This mechanism is studied herein using in-situ indentation experiments performed at two dierent scales. The rst test was carried out in a lab tomograph. The second test was conducted on the high resolution synchrotron ID19 beamline at ESRF. Very early damage is revealed. The basic mechanism of pore collapse and its gradual development is detected in contrast with mesoscale observations where compaction appears very abrupt.

International audience; We use multiscale modelings to investigate the heat dissipation in 2D transistors based on phosphorene and silicene. First, molecular dynamics (MD) simulations were used to calculate the thermal interface resistance R int between the 2D materials (phosphorene and silicene) and dielectrics substrates (SiO 2 and TiO 2). The calculated R int of these systems are close to that between graphene and SiO 2 and are insensitive to the temperature. The MD values then served as inputs for finite-element simulations at the device scale. It is found that the heat-dissipation ability of the 2D transistors can be improved by increasing the thermal conductivities of the 2D materials as well as of the substrate. However, in contrast to the common belief, it is difficult to largely reduce the hot-spot temperature by tuning the interface thermal resistance. Finally, we show that the cooling performance of silicene/SiO 2 system can be significantly improved with a few-layer graphene heat spreader. These results provide important information for the novel design of 2D transistors in terms of thermal management.

International audience; PTFE presents an original secondary crystallization that appears to be independent of the primary one. The conjunction of differential scanning calorimetry and dilatometry experiments has offered complementary data to study both crystallization melted compacted powder and of recrystallized samples. The primary crystallization is responsible for the crystallinity content variation with the cooling rate. It preserves the anisotropy induced by previous compaction that can be observed by dilatometry. Conversely, the secondary crystallization appears to be instantaneous, reversible, kinetic-free and isotropic. It occurs over a wide temperature range between 250°C and 310°C.

The charging properties of a particle during a single impact have been studied before in research. Despite these contributions, there remains incomprehension on the very mechanisms responsible for the charge transfer and predictions regarding the tribocharging of a dielectric particle against another dielectric material are still rather unreliable. Glass, found with various different chemical compositions, is a good example of a material that defies the expectations of triboelectric series. This article reports the development of a setup measuring the charge generated by a single impact between a glass bead and a dielectric. The setup is designed to control most relevant parameters to achieve the highest level of reproducibility possible, and to perform series of tests to maximize statistical relevance. Preliminary results on parameters such as the normal velocity at impact, the relative humidity and the impact angle are described.

Experiments and simulation results are compared in order to make precise the conditions optimizing both the kinetics of plaster hydration and the structure of the resulting material. Calorimetry experiments performed for different amounts of added gypsum seeds are used to assign values to the simulation parameters controlling kinetics, e.g. time step, surface density of gypsum germs on plaster grains. Simulation provides a reliable quantity to follow the beginning of setting, the fraction of gypsum needles belonging to a percolating cluster, as proven by comparing its evolution with the one of the elastic modulus during shear experiments. The simulations reveal that the beginning of needle growth may be hindered by two many small plaster grains, whereas big plaster grains slow down the end of the reaction. We suggest to add gypsum germs with an m g / m p = 0.002 gypsum-to-plaster mass ratio in order to optimize homogeneity of the final material.

Drinking water pipes can be lined with a cement matrix based on CEM III, which can release aluminium into the water. However, the European Union limits the aluminium concentration in drinking water for public health reasons. In order to study the long-term leaching mechanism of aluminium, semi-dynamic leaching tests using an aggressive solution (demineralised water) or drinking water (mineralised water) were conducted on crushed CEM III pastes maintained at pH 7. They resulted in a very high leaching coefficient, approaching 50%. However, in spite of this strong leaching, the amount of Al leached remained very low, at less than 1.5% of the initial amount of Al in the material. Under these conditions, the leaching of Al from a CEM III paste is complex since it involves several steps, where slag (1st and last steps) or cement paste (2nd step) are the main contributors.

International audience; To design lightweight plasterboard and optimize the compromise between thermal resistance and mechanical strength, it is important to characterize its strength as characterized with the normative Nail pull test. Understanding the phenomenology of this test is the key to identifying the limiting factor in terms of load carrying capacity. In this work, the degradation mechanisms of lightweight plasterboard are analyzed via tests conducted in-situ in a laboratory tomograph. Through the analysis of the kinematics by digital volume correlation, the dierent mechanisms at play up to failure mechanism have been identied, i.e., quasi-elastic regime, failure of the roller coating layer, core compaction and core failure. The compaction of the core by the collapse of porosity in compression is recognized as the limiting factor in terms of compressive strength and tearing resistance.

International audience; Cold uniaxial pressed PTFE compacts were subjected to thermal cycles of increasing maximum temperature below melting temperature, and thermal expansion was followed in both the compaction and transverse directions. The measurements reveal that thermal expansion consists of two distinct contributions: i) an irreversible part that is controlled only by the maximum temperature experienced by the sample, and ii) a reversible, or thermo-elastic, part that is observed while cycling below the maximum temperature. Moreover, both of these thermal strains exhibit marked anisotropy, resulting from the cold oedometric compaction of the sample. A quantitative analysis of these eigenstrains is proposed, following a formal analogy with elasto-plasticity. Finally, it is shown that such behavior is specific to cold-pressed compacts as sintered samples exhibit isotropic and purely reversible thermo-elastic behavior.

International audience; For decades, poly(vinylbutyral) (PVB) has been the polymer of choice to improve the impact resistance of laminated glass. PVB presents large rupture strain, large tensile strength and excellent dissipative properties. Here we investigate the relation between macromolecular structure and mechanical properties of plasticised PVB by combining large strain tensile experiments with calorimetry, X-ray and birefringence measurements. We find that the mechanical response is dominated by creep and that this plastic-like flow can effectively be described by a strain dependent viscosity. The commonalities with other toughened polymeric materials are outlined, and especially the role played by phase separated domains with weaker physical bonds. These results could help optimize polymer design for toughness and impact applications.

Hydrogel coatings absorb water vapor - or other solvents - and, as such, are good candidates for antifog applications. In the present study, the transfer of vapor from the atmosphere to hydrogel thin films is measured in a situation where water vapor flows alongside the coating which is set to a temperature lower that the ambient temperature. The effect of the physico-chemistry of the hydrogel film on the swelling kinetics is particularly investigated. By using model thin films of surface-grafted polymer networks with controlled thickness, varied crosslinks density, and varied affinity for water, we were able to determine the effect of the film hygroscopy on the dynamics of swelling of the film. These experimental results are accounted for by a diffusion-advection model that is supplemented with a boundary condition at the hydrogel surface: we show that the latter can be determined from the equilibrium sorption isotherms of the polymer films. Altogether, this paper offers a predictive tool for the swelling kinetics of any hydrophilic hydrogel thin films.

Dispersing carbon nanotubes (CNTs) using surfactants into water requires ultrasonication that supplies mechanical energy to debundle and exfoliate CNTs. However, sonication is known to damage CNTs and to cut them into short fragments. Also, the CNT concentration in water dispersion is typically limited to up to 1.0 wt %. Here, we show that by using a sulfuric acid pretreatment, we can enhance the debundling of CNTs and reduce subsequent sonication to achieve homogeneous dispersions without damaging CNTs. Additionally, using a progressive and controlled dialysis, we are able to increase the CNT concentration up to 1.8 wt %. We demonstrate that such highly concentrated dispersions can be used as spin dopes to fabricate continuous fibers. Our fibers have an electrical conductivity up to 580 kS/m, a tensile strength of ∼1 GPa, and a Young’s modulus of 123 GPa, exceeding the mechanical properties of related fibers made from conventional surfactant-stabilized dispersions of sonicated CNTs.

International audience; Foams made with polymer hydrogels can be used in a variety of applications, such as scaffolds for biomedical applications or decontamination processes. However, from a practical point of view, it is difficult to introduce bubbles into viscous or viscoelastic fluids and to produce large volumes of hydrogel foams. In the present article, we investigate the foaming process of poly(vinyl alcohol) (PVA)/borax transient hydrogels, where PVA chains reversibly bind to borax molecules. In a previous article, we showed that foams obtained with PVA/borax mixtures are highly stable because of both high interfacial and bulk viscosities and can be used to quickly absorb liquids, which make them suitable for detergency or decontamination processes. To produce these foams, we use a two-step foaming process which consists in first shearing a PVA solution to obtain a PVA foam and second adding borax to the PVA foam under continuous shearing. The obtained PVA/borax foams are stable for weeks. In this study, we observe a shear-induced collapse of the foams for formulations containing a low borax/PVA ratio, whereas they remain stable under shear for high PVA/borax ratios. Using scaling arguments, we find that the shear-induced collapse of the foams and bubbles is obtained below a critical ratio, NE/NB = 15, of the number of entanglements per chain, NE, and the number of borax per chain, NB. Rheology measurements show that the samples present a shear-thickening behavior that increases with the borax concentration. We suggest that during the foaming process when the shearing rate is of the order of 100 s–1, the viscosity of these samples diverges, leading to a viscous to fragile transition. To mimic the fast stretching of the PVA/borax thin films during the foaming process, we study the stretching of individual PVA/borax catenoid-shaped thin films at high stretching rates. We observe that the films containing low PVA/borax ratios do not minimize their surface area unlike what is theoretically expected for standard surfactant films. Moreover, the films tend to be unstable and fracture because the PVA/borax network does not have time to rearrange and relax stresses for high stretching rates.

Lignosulfonates (LS) are water-soluble polyphenolic macromolecules derived from lignins and common industrial additives in plasticizers and dispersants. A key feature for a more efficient utilization of modified LS is the monitoring of their free phenol (OHphen) content during various reactions as these phenols govern a large part of their chemical reactivity. Against this background, the UV difference spectroscopy (Δεi method) and ClO2 titration have been revisited. Synthetic LS model compounds with a SO3H group on their benzylic position and H, G, and S aromatic rings were synthesized and used to assess the suitability of both the ClO2 titration and the Δεi method on LS. The methodology combining the two analytical methods was then used to determine the molar extinction coefficient of a given LS allowing the calibration of the Δεi method for a convenient and rapid monitoring of OHphen in the course of LS reactions involving the OHphen groups.

Slippery liquid-infused porous surfaces (SLIPS) are porous nanostructures impregnated with a low surface tension lubricant. They have recently shown great promise in various applications that require non-wettable superhydrophobic surfaces. In this paper, we investigate experimentally the influence of the oil thickness on the wetting properties and drop impact dynamics of new SLIPS. By tuning the thickness of the oil layer deposited through spin-coating, we show that a sufficiently thick layer of oil is necessary to avoid dewetting spots on the porous nanostructure and thus increasing the homogeneity of the liquid distribution. Drop impact on these surfaces is investigated with a particular emphasis on the spreading and rebound dynamics when varying the oil thickness and the Weber number.

International audience; Plasterboards are tested in four-point bending up to failure, and digital image correlation is used to follow the kinematics and the progressive degradation of the structure all along the test. Although numerous distinct core cracks are clearly observed, it is proposed to identify the behavior of plasterboard through a homogenized continuum description where the progressive degradation of the bending stiffness is described through a damage law. A specific procedure for the identification is presented where experimental imperfections and symmetry breakdown are accepted and accounted for. The identification procedure is shown to provide constitutive parameters with a very small variability.

International audience; Reinforcing clamps made of low alloy steel from the Metz cathedral and corroded outdoors during 500 years were studied by OM, FESEM/EDS, and micro-Raman spectroscopy. The corrosion product layer is constituted of a dual structure. The outer layer is mainly constituted of goethite and lepidocrocite embedding exogenous elements such as Ca and P. The inner layer is mainly constituted of ferrihydrite. The behaviour of the inner layer under conditions simulating the wetting stage of the RH wet/dry atmospheric corrosion cycle was observed by in situ micro-Raman spectroscopy. The disappearance of ferrihydrite near the metal/oxide interface strongly suggests a mechanism of reductive dissolution caused by the oxidation of the metallic substrate and was observed for the first time in situ on an archaeological system.

International audience; Erbium-doped fiber amplifiers (EDFAs) for harsh environments require to develop specific fabrication methods of Er 3+-doped fibers (EDFs) so as to limit the impact of radiation-induced absorption. In this context, a compromise has to be found between the concentration of Erbium and the glass composition. On the one hand, high concentration of Er 3+ ions helps to reduce the length of the EDF and hence the cumulated attenuation but generally leads to luminescence quenching mechanisms that limit the performances. On the other hand, so as to avoid such quenching effect, glass modifiers like Al 3+ or P 5+ ions are used in the fabrication of commercial EDFs but are not suitable for applications in harsh environment because these glass modifiers are precursors of radiation-induced structural defects and consequently of optical losses. In this work, we investigate the concept of smart doping via material nanostructuring as a way to fabricate more efficient optical devices. This approach aims at optimizing the glass composition of the fiber core in order to use the minimal content of glass modifiers needed to reach the suited level of performances for EDFA. Er 3+-doped alumina nanoparticles (NPs), as precursor of Er 3+ ions in the preform fabrication process, were used to control the environment of rare-earth ions and their optical properties. Structural and optical characterizations of NP-doped preforms and optical fibers drawn from such preforms demonstrate the interest of this approach for small concentrations of aluminum in comparison to similar glass compositions obtained by a conventional technique.

Cyclic voltammetry ( CV ) and electrochemical impedance spectroscopy ( EIS ) were used to characterize the tarnished thin layer of silver deposited on glass. Instead of natural tarnishing in air environment, an acceleration of tarnishing process was realized by immersion of Ag covered glass in 10 μM K 2 S medium. The X-ray photoelectron spectroscopy ( XPS ) shows that tarnishing product formed on the silver surface consisted of Ag 2 S and Ag 2 O. As electrochemical characterization, the measurements were carried out in aerated 0.5 M Na 2 SO 4 solution adjusted at pH 10. The impedance spectra collected in sulphate medium at the open-circuit potential show one capacitive loop in parallel with a high resistance, which reflects a blocking electrode behaviour. However, the equivalent electrical circuit, R s -(CPE// R ) is insufficient to reproduce the experimental results correctly. To minimize the dispersion between the experimental and fitted data, the CPE contribution is replaced by two normal power-law distributions of the local resistivity to interpret the tarnishing process in K 2 S medium with respect to the immersion time. These distributions are associated with the Ag 2 S and Ag 2 O layers.

International audience; There is currently a growing interest in nano-structured silica based materials due to their remarkable thermal properties. These materials are notably used in Vacuum Insulating Panels (VIP). Their exceptional insulating performances have been demonstrated experimentally for a relatively long time. But the heat transfer mechanisms occurring in this kind of materials remain relatively badly known due to the nanometric dimensions and to the complexity of the porous structure. Therefore, the present study aims to develop a numerical model for estimating the magnitude of conductive heat transfer inside nano-structured silicas using a realistic representation of their complex porous structure. The model takes into account the special porous morphology of the materials at both the nanometric and microscopic scale. Moreover, the conduction heat transfer at the nanometric scale is treated using a numerical resolution of the Boltzmann equation since the validity of the macroscopic laws is then questionable. The computations are conducted using phonon properties of silica obtained in the literature. A parametric study allows us to analyse the influence of structural characteristics and thermo-physical properties on the insulating performances and thus to highlight the most important parameters.

In this article we examine the foamability and foam stability of a series of PEI/silica gel suspensions with varying particle concentrations in the presence of a neutral surfactant, C 12 E 23 . These suspensions, which were recently developed for 3D printing applications, exhibit a finite yield stress whose value can be tuned by varying the particle concentration and the pH. Our study aims at evaluating whether this system is suitable to produce stable foams that could be further be used as precursors for the 3D printing of porous materials and to evaluate the relation between the yield stress and the foam stability against drainage and ripening. At pH7 where all the suspensions are in the fluid state, the maximum air fraction reaches 80% however the foams are very unstable to drainage. At pH 10.5, the suspensions are in the gel state due to Van der Waals driven aggregation of the particles. In the gel state, the obtained maximum air fraction decreases with the suspension concentration, from ϕ air = 80% for the 12.8 wt% suspension to ϕ air = 65% for the 15.5 wt% suspension. The most concentrated suspension, i.e 19.7 wt% could not be foamed. At pH 10.5, the yield stress of the 12.8 wt% suspension is 10 Pa, which enables to overcome the buoyancy acting on the particles and therefore arrest drainage. However the yield stress is too low to overcome the Laplace pressure in the bubbles, therefore Ostwald ripening is observed. The 15.5 wt% suspension exhibits a yield stress of 200 Pa, which is high enough to arrest drainage. Ostwald ripening occurs at early times and is arrested when the bubble radius reaches 400 μm as the yield stress equals the Laplace pressure. The results obtained in this study show that there is an optimal silica concentration which combines good foamability and large stability to drainage and Ostwald ripening. These materials are promising for the development of 3D printable foams even though the size of the bubbles will limit the spatial resolution of the printing to a few millimeters.

International audience; In the dynamic rupture of laminated glass, it is essential to maximize energy dissipation. To investigate the mechanisms of energy dissipation we have experimentally studied the delamination and stretching of a polymeric viscoelastic interlayer sandwiched between glass plates. We find that there is a velocity and temperature domain in which delamination fronts propagate in a steady state manner. At lower velocities, fronts are unstable while at higher velocities, the polymer ruptures. Studying the influence of the interlayer thickness, we have shown that the macroscopic work of fracture during the delamination of the interlayer can be divided in two main components: 1. A near crack work of fracture which is related to the interfacial rupture and to the polymer deformation in the crack vicinity. 2. A bulk stretching work which relates to the stretching of the interlayer behind the delamination front. Digital Image Correlation measurements showed that the characteristic length scale over which this stretching occurs is of the order of the interlayer thickness. Finally, an estimate of the bulk stretching work was provided, based on a simple uniaxial tensile test

Compaction of the core of plasterboard is one of the limiting phenomena for its mechanical performance. This mechanism is studied herein in an indentation test. A cylinder made of foamed gypsum is indented in situ in an X-ray lab tomograph with a sphere of millimeter radius. The reported experiments show that foamed plaster displays a sharp transition between an undamaged state (with linear elastic behavior) and a compacted state with collapsed porosity under the indenter. Tomographic acquisitions of the sample under load associated with a global version of Digital Volume Correlation allow displacement fields to be measured at different load levels. However, because of the heterogeneous nature of the indentation test, a fine spatial resolution of the displacement fields is required to measure the strains at the crushing limit. A dedicated procedure exploiting computed displacement fields within the digital volume correlation procedure is utilized. It allows for the quantification of stress fields that are post-processed to identify the crushing criterion. It is shown that this analysis is very consistent with more macroscopic oedometric tests. Last, predictions of a Mohr–Coulomb model are compared with macroscopic and microscopic data. It is shown that despite the fact that this model reproduces very well the load–displacement response of the indentation test, a poorer prediction of the experimental crushed zone is observed. In particular, the transition between compacted plaster and its pristine state is not captured by the model, which predicts a very progressive transition rather than an abrupt one. The same conclusions are drawn for a crushable foam model when compared with experimental evidence of an in situ oedometric test.

International audience; Hot plate methods under steady state conditions are based on a 1D model to estimate the thermal conductivity, using measurements of the temperatures T0 and T1 of the two sides of the sample and of the heat flux crossing it. To be consistent with the hypothesis of the 1D heatflux, either a hot plate guarded apparatus is used, or the temperature is measured at the centre of the sample. On one hand the latter method can be used only if the ratio thickness/width of the sample is sufficiently low and on the other hand the guarded hot plate method requires large width samples (typical cross section of 0.6 × 0.6 m2). That is why both methods cannot be used for low width samples. The method presented in this paper is based on an optimal choice of the temperatures T0 and T1 compared to the ambient temperature Ta, enabling the estimation of the thermal conductivity with a centered hot plate method, by applying the 1D heat flux model. It will be shown that these optimal values do not depend on the size or on the thermal conductivity of samples (in the range 0.015–0.2 W m−1 K−1), but only on Ta. The experimental results obtained validate the method for several reference samples for values of the ratio thickness/width up to 0.3, thus enabling the measurement of the thermal conductivityof samples having a small cross-section, down to 0.045 × 0.045 m2.

International audience; Silicon nitride thin films are widely used as diffusion barriers within stacks in the glass industry but turn out to be porous at the nanometric scale. EIS measurements were conducted on SiNx thin layers deposited on a gold layer. An electrochemical model was established to fit the EIS measurementsmaking use of data from other complementary techniques. In particular, Transmission Electron Microscopy was performed on these thin layers to determine the diameter and the qualitative morphology of the pores. A quantitative determination of the through-porosity of the layer was deduced from the EIS model and was in good agreement with TEM measurements. Moreover, combining EIS with local observations enabled inhomogeneitiesin the layer to be probed by highlighting a specific region in the layer.

International audience; We consider the impact of the mechanical behaviour of polymeric coatings on glass strengthening. We have performed rupture stress measurements and compared the strengthening measured in the rubbery state and the glassy state. We evidence a moderate decrease of the strengthening when the temperature exceeds the glass transition temperature of the coating. Based on the predictions of crack bridging models, we show that the limited difference of strengthening between glassy and rubbery states can be understood if confinement of the polymer inside the crack is taken into account. Similarly, our results suggest that confinement severely limits the shear deformation of polymeric coatings and suppresses viscoelastic dissipation.

International audience; Among the existing methods, Nanoimprint Lithography (NIL) emerges as a simple route for surface patterning at the sub-micrometer scale over large areas. Thanks to their tunable properties, sol-gel materials form an alternative class of resist for NIL. However, there is only little understanding of the rheological properties responsible for their good imprint ability. Based on previous works on thermal curing of thermosets, this paper establishes a framework which can be used to tune the imprint conditions and to apprehend the rheological properties of complex hybrids materials. Using a combination of Dynamic Mechanical Analysis (DMA) and scratch test, we were able to model the thermorheological behavior of Methyltriethoxysilane (MTES) gel films during isothermal treatments in a time-temperature-transformations (TTT) diagram. Infrared spectroscopy study of the gel demonstrates the existence, for the same elaboration chemistry, of a condensation threshold independent of the temperature above which the material vitrifies: this reveals the closed relation between the rheology and the chemical microstructure of the gel. We also discussed the strong influence of the elaboration chemistry on the initial microstructure and therefore on the vitrification.

The stabilization of organic coatings by tin dioxide resulting in glass bottle lubrication was investigated on flat glass. The anchoring function of SnO 2 was assessed for a mixture of polyethylene and polymethylmethacrylate. Friction tests in air confirm the SnO 2 anchoring property with the maintaining of the lubricant effect due to the polymer over large sliding distances. The persistence of the polymethylmethacrylate stretching band ν C = O on significant sliding distances in infrared microscopy experiments shows that the polymer coating stabilization results from the strong adhesion of the polymer on SnO 2 . The impact of roughness and surface chemistry on the stabilization of the polymer coating was tested. The suppression of the lubricant effect by surface chemistry alteration or by roughness modification of SnO 2 suggests that roughness and surface chemistry of SnO 2 are both necessary for lubrication.

International audience; Poly[Styrene-b-Butadiene-b-(Methyl Methacrylate)], SBM triblock copolymers have been incorporated in different polyurethane, PU formulations in order to prepare nanostructured materials. Macrodiols used for PU synthesis were based on a central bis-phenol A, BPA unit with two hydroxyl-terminated oligo(oxypropylene), BPA-POx or oligo(oxyethylene), BPA-EO chains with varying lengths. The initial solubility of the three blocks and the rheological behavior of the solutions in macrodiols and also in two diisocyanates, isophorone diisocyanate, IPDI, and 1,3-xylylene diisocyanate, XDI have been first characterized. The PMMA block is the most soluble and its role during the reaction is to stabilize the initial nanostructure or to control the reaction-induced microphase separation. Block copolymers can be dissolved first in the macrodiol, or preferably in the diisocyanate. With BPA-POx and low SBM content (50 wt%), a twin screw extruder had to be used for the blending. Under well-defined conditions, transparent linear PUs and linear segmented polyurethane-ureas have been prepared. This study confirms that for designing a nanostructured material from a reactive mixture with a triblock additive, one block, called “the nanostructuring block” has to remain soluble up to the end of the reaction.

The unsteady diffusion equation in a tube and the advection/diffusion equation in laminar flow in a liquid of a solute are theoretically established. The most important parameters are the migration strength α and the so-called Graetz number Gr . The former dimensionless number is the product of the partition coefficient of the solute at the solid/liquid interface, the ratio of the tube thickness to the interior radius and the ratio of diffusion coefficients of the solute in the liquid and in the solid. The Graetz number Gr is the ratio of the diffusion time scale in the liquid based on the interior radius of the pipe to the advection time over the tube length. The problem is applied to the plasticizer migration from a polyvinyl chloride material to a liquid with the safety food applications in mind. The migration of the plasticizer is solved numerically for various tube sizes, flow conditions and partition coefficients of the plasticizer in the liquid. For comparison, the numerical results obtained in static condition are also provided. The average plasticizer concentration in the liquid behaves following two main regimes as a function of the migration strength. When α is much smaller than one, the average plasticizer concentration in the liquid is an algebraic function of the axial coordinate, z, at the power two third and increases linearly with time. Conversely, when α is much larger than one, the average plasticizer concentration is linear as a function of axial distance and increases as a function of the square root of time. Moreover, the concentration is much smaller of few orders of magnitude in dynamic condition than in static working showing that in the context of food contamination the dynamic approach is more appropriate and relevant for demonstration of compliance with the safety authorities requirements.

International audience; We have carried out wetting experiments on textured surfaces with high aspect ratio asperities in the Wenzel state. When inclination is imparted to the asperities, we observe a strictly unidi-rectional spreading opposite to the direction in which the asperities point. The advancing contact angle decreases markedly as inclination increases. A crude numerical analysis successfully accounts for this behaviour, highlighting the interplay between Gibbs pinning at the top of the structures and imbibition along the valleys between them. In Gibbs pinning non-linearities play a major role and we find that simple line averaging-i.e. a rule of mixture-cannot account for this evolution except for weak surface perturbations, i.e. large inclinations.

International audience; We probe the drainage and imbibition dynamics of foams in which the continuous aqueous phase is a transient gel-like network. To produce these foams, we provide a new method – a PVA (polyvinyl alcohol) solution is first foamed and then a cross-linker, Borax, is added, which binds reversibly to the PVA chains. The resulting foams are ultra-stable-over a month. We find that the typical time for gravitational drainage of the continuous phase can be slowed down from hours to several weeks by tuning the Borax concentration. We show that the Borax concentration controls both the bulk viscosity of the continuous phase and the surface viscosity of the air–water interfaces. From these results we suggest that the PVA molecules adsorbed at the bubble interfaces are highly cross-linked by the Borax molecules. We find that the capillary rise of a dyed liquid into these foams is orders of magnitude faster than the drainage flow, meaning that these foams can quickly absorb liquids. These results show that these foams could be used to clean or decontaminate surfaces covered with liquid wastes. Indeed we show that the PVA–Borax foam can easily be spread on a surface, absorb a liquid without destabilizing and be dried afterward to recover the waste.

International audience; Bismuth vanadate has attractive photocatalytic properties under visible light. The influence of structure and morphology of BiVO4 nanomaterials on its photocatalytic properties in the UV and the visible domain was investigated. The selection of different sets of synthetic parameters in aqueous solutionpH or the use of organic additivesallowed the formation of tetragonal zircon, tetragonal scheelite, and monoclinic scheelite structure and different morphologies of that last phase. First, the tetragonal zircon was found to be the only inactive structure. Then, the best material for photocatalytic degradation of rhodamine B in solution and stearic acid deposited directly on the photocatalyst is the coreshell tetragonal zircon-monoclinic scheelite system prepared in the presence of sodium dodecyl sulfate. The enhanced properties are explained by the presence of strong surface acidic sites corresponding to the presence of surface sulfate residues rather than to the specific morphology of the material. Additionally, an EPR study on the ability of BiVO4 to generate active surface radical showed that hydroxyl radicals are not generated and that superoxide ion concentration under irradiation is close to the detection threshold. Depending on the selected irradiation wavelength, bismuth vanadate may present a better photocatalytic activity than titanium oxide. It is shown to be equivalent to bismuth tungstate under blue light.

International audience; Regenerative heat exchangers used in glass industry are complex systems owing to the transient nature of their operating cycle, as well as to the complexity of the heat exchange phenomena involved: aiding mixed convection during the cold period and combined presence of radiation and forced convection during the hot period. The present study describes an open method to simulate the behaviour of such regenerators. Preliminary results allowed us to validate our model in comparison with experimental and/or analytical data obtained on simple geometries. In a second step, a complete validation is proposed on a large scale experimental set-up which reproduces the exact behaviour of an industrial glass furnace regenerator. An original method based on the Boussinesq approximation with a “fictitious thermal expansion coefficient” was successfully introduced for this complete validation.

International audience

International audience; Mass transfer around a bubble rising in a liquid under Stokes regime is investigated when a reversible chemical reaction, , is taken into account. Four dimensionless parameters control the interfacial transfer rate: the Péclet and Damköhler numbers, the ratio of the diffusion coefficient of both species, and the reaction equilibrium constant. The mass-transfer equations are solved numerically with a finite element technique. A boundary layer approach is also proposed and solved with a coupled technique of finite difference and Chebyshev-spectral method. The equilibrium constant and the ratio of diffusion coefficients have a strong influence on the coupling between the chemical reaction and mass transfer leading to an increase of the Sherwood number. The interaction between the chemical reaction and advection is clearly established by the simulations. Conditions corresponding to Péclet number larger than the Damköhler number reduces the effect of the chemical reaction.

International audience; We investigate the stabilization of air-water interfaces by mixtures of negatively charged latex particles (sulfate polystyrene) and cationic surfactants (alkyl trimethylammonium bromides). First we report results concerning the binding of surfactant molecules to the latex particles. As the surfactant concentration increases, the charge of the particles reverses, from negative to positive, because C(n)TAB first binds electrostatically to the latex particles and then through hydrophobic interaction with the monolayer already adsorbed on the particles as well as directly with the hydrophobic surface of the latex. Over a large range of surfactant concentrations around the charge inversion, a strong flocculation is observed and 100 mu m large aggregates form in the suspension. Unlike previous studies published on mixtures of inorganic particles with oppositely charged surfactants, we show that we can vary the sign of the zeta potential of the particles without changing the contact angle of the particles over a large range of surfactant concentrations. Indeed, the latex particles that we study are more hydrophobic than inorganic particles, hence adding moderate concentrations of the surfactant results in a weak variation of the contact angle while the charge of the particles can be reversed. This enables decoupling of the effect of zeta potential and contact angle on the interfacial properties of the mixtures. Our study shows that the contact angle and the charge of the particles are not sufficient parameters to control the foam properties, and the key-parameters are the flocculation state and the shear energy applied to produce the foam. Indeed, flocculated samples, whatever the sign of the zeta potential, enable production of a stable armour at the interface. The large aggregates do not adsorb spontaneously at the interface because of their large size, however when a large shear energy is used to produce the foam very stable foam is obtained, where particles are trapped at interfaces. We suggest that the large aggregates may be broken during shear and may reform at the interface to form a solid armour. A simple calculation taking into account the adsorption dynamics of the aggregates as a function of their size is consistent with this hypothesis.

International audience; The optimization of functional optical devices requires the appropriate control of light propagation, which can be achieved by using engineered dielectric structures. Innovative materials combination and fabrication strategies are required to achieve a robust gain in performance without impacting manufacturing complexity and cost. In the present work, a novel liquid-based approach is proposed for the simple and scalable fabrication of highly effi - cient and robust optical multilayer dielectric coatings. In particular, a sol-gel process is developed that enables the fabrication of large-area distributed Bragg refl ectors (DBR) integrating macroporous materials of controlled closed porosity. The DBRs have a very high index contrast, excellent and tunable optical properties, and high stability of performance and structural integrity with respect to crack formation and delamination, even against harsh ageing tests or solvent exposure. The potential of this approach to be integrated within existing optoelectronic architectures is demonstrated through the integration of a DBR structure as a back refl ector in an amorphous silicon solar cell (a-Si:H), resulting in a signifi cant increase in light absorption, photocurrent, and overall effi ciency. This opens the way towards simple dielectric engineering of robust photoactive devices based on the versatile use of liquid routes for the deposition of structured dielectric coatings.

International audience; Bismuth tungstate has attractive photocatalytic properties under visible light. A better understanding of the origin of that good activity should allow its control and its optimization. An improved photocatalytic activity to different pollutants was obtained using bismuth-based oxide obtained by microwave-assisted synthesis combined with the addition of sodium dodecylsulfate as a size tailoring agent. It is shown using electron paramagnetic resonance that bismuth tungstate is able to generate hydroxyl radicals in aqueous aerated solution, but no superoxide radical anions are formed. The catalytic efficiency relative to TiO2 could be associated to differences in the number of excitons generated, to their lifetimes as holes and electrons in the semiconductor, and to valence and conduction band positions.

International audience; The moisture distribution during the setting of a thin mortar layer can be particularly complex to manage under dry (20% RH) and hot weather (above 25 degrees C) conditions. To better understand the fundamental phenomena at stake, we used static gradient relaxation NMR tools such as Profile MOUSE and STRAFI. This allowed disentangling the mutual effect of evaporation and self-desiccation by hydration. The interest of combining the two techniques is that the capillary water is observed with the MOUSE while STRAFI reveals quantitatively the build-up of the hydrate gel nanostructure. Spatially resolved and 2D relaxation exchange experiments on a model white cement paste revealed that although evaporation induced a capillary water gradient, the kinetics of the building of the pore structure and its homogeneity remained unaffected

The redox of alkaline-earth silicates with iron concentrations ranging from 150 to 5000 ppm was measured using X-ray absorption spectroscopy at the K-edge of iron, in fluorescence mode. These measurements were carried out at three beam lines with different characteristics: FAME (BM30) and DUBBLE (BM26) at ESRF (Grenoble, France) and XAFS2 at LNLS (Campinas, Brazil). In those conducted at BM26, we observed X-ray photoreduction of iron in soda-lime silicate glasses, and we studied it systematically as a function of the iron content of the samples. The photoreduction due to the X-ray beam has a critical impact on the redox measurements at room temperature for glasses with iron contents below 1000 ppm. Results show that a constant amount of Fe3 + seems to be reduced by the beam, regardless of the total iron content within the sample. A tentative explanation for this phenomenon is proposed. The photoreduction effect is reversible and can be prevented by making the measurements at a temperature of 450–500 °C, instead of room temperature. Using this new measurement protocol, the redox state at equilibrium with air of a family of glasses with iron contents ranging from 150 to 5000 ppm has been analysed and compared to values obtained by wet chemistry analyses and additional results by Densem and Turner (1938). Wet chemical analysis, commonly used nowadays, does not show any particular variation of the redox with iron content. XANES results indicate a more complex behaviour where the redox increases as the amount of iron decreases, which is in closer agreement with the early results by Densem and Turner (1938) obtained with a different wet chemical analysis protocol no longer used.

International audience; The structure of two borosilicate glasses and melts has been investigated by neutron diffraction coupled with Reverse Monte Carlo (RMC) simulation. For both compositions (10B2O3 ⋅ 30Na2O ⋅ 60SiO2 and 10B2O3 ⋅ 15Na2O ⋅ 15CaO ⋅ 60SiO2), the fraction of tetrahedral boron ([4]B) drops from 0.7 to 0.3 from the glass to the melt. The change from a modifying to a charge compensating role of cations during quench is related to the boron coordination change. These molecular scalemodifications explain the low viscosity of alkali/alkaline-earth borosilicate melts relative to alkali/alkaline-earth silicate melts, as the viscous flow is enhanced with the proportion of [3]B. RMC simulations of soda borosilicate glass and melt show a preferential interbonding between B and Si polyhedra. Such medium range order interbonding is unfavored in the soda-lime borosilicate glass showing a nearly random network. The effect of Ca enhancing the proportion of B-B pairs is here highlighted.

International audience; Enhanced control of diffraction through transparent substrates is achieved via disordered gratings in a silica sol-gel film. Tailoring the degree of disorder allows tuning of the diffractive behavior from discrete orders into broad distributions over large angular range. Gratings of optical quality are formed by silica sol-gel nanoimprint lithography and an optical setup for the measurement of continuous diffraction patterns is presented. Sound agreement is found between measurements and simulation, validating both the approach for redirection of light and the fabrication process. The disordered gratings are presented in the context of improved interior daylighting and may furthermore be suited to a wide variety of applications where controlled angular redirection of light is desired.

The goal purchased in this paper is to implement a pulse method to measure the thermal conductivity of liquid silica glass above 1200°C until 1600°C. A heat flux stimulation controlled in energy and in time is generated on the front face of an experimental cell. The temperature rise is measured on the rear face of this cell face by using a fast cooled infrared camera. The choice of the measurement cell geometry is fundamental to be able to estimate at the same time the thermal diffusivity and the specific heat of the liquid by an inverse technique. The parameters estimation problem takes into account the optimization of the cell wall thickness. The theoretical model used for the inversion takes into account the coupled heat transfer modes (conduction, convection and radiation) that can occur during the experiment, particularly the thermal conductive short-cut through metallic lateral walls of the cell and radiative transfer within the semi-transparent and participating medium. First measurements are performed on a cell filled with water at ambient temperature in order to validate the parameters estimation procedure.