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Granular materials are ubiquitous, both in nature and in industry or in our daily life. Blending grains and liquid is a basic operation at the origin of many industrial processes. Nevertheless, the understanding and the modeling of the mechanisms of exchanges of liquid and grains, implied in the mixing process, remain largely unknown. In this PhD, we propose to investigate the mechanisms of interactions between a granular material containing a variable quantity of liquid and flowing dry grains. Depending on the amount of liquid, the wet granular phase can be eroded by the granular flow, or flowing grains can be captured by granular accretion or the liquid can be transported from the wet to the dry phase by impregnation. First, we focus on the mechanisms and the dynamics of granular accretion observed after the impact of a dilute granular jet on a wet granular substrate. We highlight the role of liquid interfaces on the growth dynamics and the sources of energy dissipations implied in the capture. Then, using an experiment of accretion with a dense and shear granular flow, we study the influence of the flow properties on the dynamics of capture and we propose a general accretion law. The rotating drum configuration with an isolated aggregate in a granular flow allows us to extend our investigation with the situation of unsaturated granular materials growing by accretion before being eroded. In the second part of the PhD, we study the impregnation in a dense granular jet penetrating into a liquid bath. By modeling the grains intrusion as the impregnation of a porous medium, we highlight the link between the shape of the front profile and the immersion speed. We also characterize the influence of the physico-chemical properties of the grains. This work constitutes a first step in the understanding of local phenomena implied in granular blending processes and the transition from dry to wet granular media.; Les matériaux granulaires sont omniprésents, tant dans la nature que dans l'industrie ou dans notre vie quotidienne. Les mélanger à un liquide constitue une opération de base dans de nombreux procédés industriels. Néanmoins, la compréhension et la modélisation des mécanismes d'échanges de liquide et de grains impliqués dans le mélange restent encore méconnus. Dans cette thèse, nous considérons les mécanismes d'interactions apparaissant à l'interface entre un matériau granulaire contenant une quantité variable de liquide et un écoulement de grains secs. En fonction de la quantité de liquide, la phase granulaire humide est soit érodée par l'écoulement sec, soit capte des grains par accrétion granulaire, soit transfère du liquide de la phase humide à la phase sèche par imprégnation. Dans un premier temps, nous nous intéressons aux mécanismes et aux dynamiques d'accrétion granulaire observés lors de l'impact d'un jet dilué de grains secs sur un substrat granulaire saturé en liquide. Nous mettons en avant le rôle du liquide aux interfaces dans la dynamique de croissance et les sources de dissipations énergétiques responsables de la capture des grains secs. Une expérience d'accrétion dans un écoulement dense et cisaillé permet ensuite d'étudier l'influence des propriétés de l'écoulement sur la dynamique de capture et d'établir une loi d'accrétion générale. Une configuration d'accrétion d'un agrégat isolé au sein d'un écoulement granulaire en tambour tournant permet enfin d'étendre notre étude au cas des matériaux granulaires non saturés en liquide, croissant par accrétion avant de s'éroder. Dans un second temps, nous étudions l'imprégnation dans un jet granulaire dense pénétrant dans un réservoir de liquide. En modélisant l'entrée des grains dans l'eau comme l'imprégnation d'un matériau poreux, nous mettons en évidence une relation entre la forme du front d'imbibition et la vitesse d'immersion, et caractérisons l'effet des propriétés physico-chimiques des grains. Ces travaux constituent une avancée dans la compréhension des phénomènes locaux impliqués dans le mélange entre grains et liquide et de la transition d'un milieu granulaire sec à humide.

Granular materials are ubiquitous, both in nature and in industry or in our daily life. Blending grains and liquid is a basic operation at the origin of many industrial processes. Nevertheless, the understanding and the modeling of the mechanisms of exchanges of liquid and grains, implied in the mixing process, remain largely unknown. In this PhD, we propose to investigate the mechanisms of interactions between a granular material containing a variable quantity of liquid and flowing dry grains. Depending on the amount of liquid, the wet granular phase can be eroded by the granular flow, or flowing grains can be captured by granular accretion or the liquid can be transported from the wet to the dry phase by impregnation. First, we focus on the mechanisms and the dynamics of granular accretion observed after the impact of a dilute granular jet on a wet granular substrate. We highlight the role of liquid interfaces on the growth dynamics and the sources of energy dissipations implied in the capture. Then, using an experiment of accretion with a dense and shear granular flow, we study the influence of the flow properties on the dynamics of capture and we propose a general accretion law. The rotating drum configuration with an isolated aggregate in a granular flow allows us to extend our investigation with the situation of unsaturated granular materials growing by accretion before being eroded. In the second part of the PhD, we study the impregnation in a dense granular jet penetrating into a liquid bath. By modeling the grains intrusion as the impregnation of a porous medium, we highlight the link between the shape of the front profile and the immersion speed. We also characterize the influence of the physico-chemical properties of the grains. This work constitutes a first step in the understanding of local phenomena implied in granular blending processes and the transition from dry to wet granular media.; Les matériaux granulaires sont omniprésents, tant dans la nature que dans l'industrie ou dans notre vie quotidienne. Les mélanger à un liquide constitue une opération de base dans de nombreux procédés industriels. Néanmoins, la compréhension et la modélisation des mécanismes d'échanges de liquide et de grains impliqués dans le mélange restent encore méconnus. Dans cette thèse, nous considérons les mécanismes d'interactions apparaissant à l'interface entre un matériau granulaire contenant une quantité variable de liquide et un écoulement de grains secs. En fonction de la quantité de liquide, la phase granulaire humide est soit érodée par l'écoulement sec, soit capte des grains par accrétion granulaire, soit transfère du liquide de la phase humide à la phase sèche par imprégnation. Dans un premier temps, nous nous intéressons aux mécanismes et aux dynamiques d'accrétion granulaire observés lors de l'impact d'un jet dilué de grains secs sur un substrat granulaire saturé en liquide. Nous mettons en avant le rôle du liquide aux interfaces dans la dynamique de croissance et les sources de dissipations énergétiques responsables de la capture des grains secs. Une expérience d'accrétion dans un écoulement dense et cisaillé permet ensuite d'étudier l'influence des propriétés de l'écoulement sur la dynamique de capture et d'établir une loi d'accrétion générale. Une configuration d'accrétion d'un agrégat isolé au sein d'un écoulement granulaire en tambour tournant permet enfin d'étendre notre étude au cas des matériaux granulaires non saturés en liquide, croissant par accrétion avant de s'éroder. Dans un second temps, nous étudions l'imprégnation dans un jet granulaire dense pénétrant dans un réservoir de liquide. En modélisant l'entrée des grains dans l'eau comme l'imprégnation d'un matériau poreux, nous mettons en évidence une relation entre la forme du front d'imbibition et la vitesse d'immersion, et caractérisons l'effet des propriétés physico-chimiques des grains. Ces travaux constituent une avancée dans la compréhension des phénomènes locaux impliqués dans le mélange entre grains et liquide et de la transition d'un milieu granulaire sec à humide.

International audience

International audience

The freezing of colloidal suspensions is encountered in many natural and engineering processes such as the freezing of soils, food engineering, and cryobiology. It can also be used as a bio-inspired, versatile, and environmentally-friendly processing route for porous materials and composites. Yet, it is still a puzzling phenomenon with many unexplained features, due to the complexity of the system and the space and time scales at which the process should be investigated. We demonstrate here the interest of fast X-ray computed tomography to provide time-lapse, three-dimensional, in situ imaging of ice crystal growth in a colloidal silica suspension. The experimental measurements show that the local increase of colloid concentration does not affect the growth kinetics of the crystals, until the colloidal particles become closely packed. For particles much smaller than ice crystals, the concentrated colloidal suspension is equivalent to a simple liquid phase with higher viscosity and a freezing point determined by the concentration of colloidal particles., 22 pages, 12 figures

International audience; Applying mechanical perturbations in a granular assembly may rearrange the configuration of the particles. However, the spatial propagation of an event is not related to the size of the external perturbation alone. Thus, the characteristic length scale of an event is not well defined. In this study, we trigger rearrangements by driving two intruders through a vertical two-dimensional packing of disks. The amplitude of the rearrangements of the granular assembly appearing around the two evolving intruders is related to their separating distances. We show that there exists a characteristic distance between intruders under which the dynamics of the grains above one intruder is influenced by the other. The size of the intruders has little effect on this characteristic length. Finally, we show that the correlation between the movements of the grains decreases with the distance away from the intruders over a larger length scale.

International audience; The second harmonic method is a dynamic indentation technique independent of the direct indentation depth measurement. It can be used to determine near-surface mechanical properties of bulk materials more precisely than classical dynamic nano-indentation. In this paper, the second harmonic method is extended to the measurement of the mechanical properties of thin PMMA layers deposited onto silicon wafers. It is shown that this new technique gives precise results at small depths (less than 100nm), even for films with a thickness lower than 500nm, which was not possible to achieve with the classical CSM method. However, experimental and numerical results obtained both with classical nanoindentation and second harmonic methods differ at high indentation depth. Using FE simulations and AFM measurements, it is shown that the contact depth calculation with classical models can explain this difference.

We investigate experimentally the local erosion of a granular bed near a fixed vertical cylinder that emerges from the bed. The onset of erosion arising at the base of the cylinder and usually ascribed to the wrapping horseshoe vortex is determined and rationalized by a flow contraction effect. We report a new erosion pattern visible downstream of the cylinder that consists of two side-by-side elongated holes. This pattern is observed for flow regimes close to the horseshoe scour onset, whose growth usually inhibits its spatiotemporal development., 6 pages, 6 figures

If confocal microscopy is an ubiquitous tool in life science, its applications in chemistry and materials science are still, in comparison, very limited. Of particular interest in these domains is the use of confocal microscopy to investigate temperature-dependent phenomena such as self-assembly, diffusio- or thermophoresis, or crystal growth. Several hurdles must be solved to develop a temperature-controlled stage for laser scanning confocal microscopy, in particular regarding the influence of an elevated temperature gradient close to the microscope objective, which most people try very hard to avoid. Here we report the design of a temperature-controlled stage able to generate stable temperature gradients in both positive and negative temperature range and does not require use of liquid nitrogen. Our setup provides an excellent control of the temperature gradient, which can be coupled with a controlled displacement of the sample, making it useful in particular for a variety of solidification, chemistry, and interfacial problems. We illustrate the benefits of our setup with several case studies of interest in chemistry and materials science: the 3D real-time imaging of ice growth, the segregation of hard particles by growing crystals, the freezing behaviour of single emulsions, the self-shaping of oil droplets upon cooling, and the self-assembly of amphiphile molecules into helical structures. These results show how confocal microscopy coupled with a temperature-controlled stage is a welcome addition to the toolkit of chemists and materials scientists., Comment: 31 pages, 9 figures

A liquid drop sitting on an elastic rod may act as a winch, or windlass, and pull the rod inside itself and coil it. This windlass effect has been shown to be generated by surface tension forces and to work best for small systems. Here we study the case where the drop is large enough so that its weight interferes with surface tension and modifies the windlass mechanics., Comment: 4 pages, 5 figures

International audience; In this work, we report an innovative route for the manufacturing of functional ceramic supports, by combining ice templating of yttria stabilized zirconia (YSZ) and atomic layer deposition (ALD) of Al 2 O 3 processes. Ceramic YSZ monoliths are prepared using the ice-templating process, which is based on the controlled crystallization of water following a thermal gradient. Sublimation of the ice and the sintering of the material reveal the straight micrometer sized pores shaped by the ice crystal growth. The high temperature sintering allows for the ceramic materials to present excellent mechanical strength and porosities of 67%. Next, the conformality benefit of ALD is used to deposit an alumina coating at the surface of the YSZ pores, in order to obtain a functional material. The Al 2 O 3 thin films obtained by ALD are 100 nm thick and conformally deposited within the macroporous ceramic supports, as shown by SEM and EDS analysis. Mercury intrusion experiments revealed a reduction of the entrance pore diameter, in line with the growth per cycle of 2 Å of the ALD process. In addition to the manufacture of the innovative ceramic nanomaterials, this article also describes the fine characterization of the coatings obtained using mercury intrusion, SEM and XRD analysis.

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.

Interdiffusion processes between aluminum enriched PVD-sputtered silica thin films and industrial float soda-lime silicate glass substrates are quantitatively studied using SIMS analysis. Heat treatments are performed at temperatures close or above the glass transition temperature of the float glass. Aluminum doping of the film is shown to strongly increase the migration of alkali from the glass substrate to the silica thin film. In particular the final alkali content in the film exhibits a linear scaling with the aluminum concentration. An interdiffusion process is evidenced between bulk alkali ions and protons originating from a significant water content in the as-deposited silica film. Experimental measurements of sodium concentration are shown to be consistent with a simple thermodynamic model based on the equilibration of the activity of sodium between the film and the glass substrate. This article is protected by copyright. All rights reserved.

When light interacts with an object, two types of phenomena can occur: light can be either absorbed or redirected by the object. The latter phenomenon is generally referred to as light scattering. Despite the significant efforts over the past decades of the scientific community, light scattering from rough surfaces remains a complex problem. This is partly due to the high degree of multidisciplinary that is required for its study. The present multidisciplinary study is related to four scientific domains that must be examined to consider the full light scattering phenomenon. First, a large panel of a rough surface, elaborated by ourselves in the laboratory or manufactured industrially, is selected for its wide range of visual aspect. The morphology of the samples are characterized using three experimental tools which allow us to describe their surface morphologies over four decades of spatial frequencies. Then the angular intensity distributions of the light scattered from the samples are measured which confirm the wide variety of optical properties of the samples. Finally, these reliable and representative experimental data are compared to the results of different light scattering models, based on both the physical and the geometrical optics approaches. The main conclusion we drew from this work is that for the examined surfaces, the light scattering can be approximated fairly well by a model based on the physical optics approach, while at the same time, geometrical optics models are not able to give an adequate description of the same scattering data., Lorsque la lumière interagit avec un objet, deux phénomènes peuvent avoir lieu : la lumière peut être absorbée ou déviée par l’objet, ce dernier phénomène étant généralement qualifié de diffusion de la lumière. Malgré l’intérêt de la communauté scientifique au cours des dernières décennies, la diffusion de la lumière induite par des surfaces rugueuses reste un problème complexe à traiter, ceci étant principalement dû à la grande multidisciplinarité requise pour l’étude du phénomène. Ce travail multidisciplinaire est basé sur l’étude de quatre différents domaines scientifiques qui doivent être considérés en parallèle pour traiter le phénomène de diffusion de la lumière de manière globale. Une vingtaine d’échantillons, fabriqués au laboratoire ou par des procédés industriels, sont sélectionnés pour leurs différentes apparences visuelles. Leur morphologie est caractérisée grâce à trois dispositifs expérimentaux, qui permettent ainsi de décrire la rugosité sur quatre décades de fréquences spatiales. Ensuite, la distribution angulaire de l’intensité lumineuse diffusée par les échantillons est mesurée, et confirme la grande variété des propriétés optiques des surfaces examinées. Finalement, ces données expérimentales sont utilisées et comparées aux résultats de deux types de modèles de diffusion de la lumière, l’un basé sur l’optique géométrique et l’autre sur l’optique physique. L’étude montre que les propriétés optiques des échantillons étudiés peuvent être assez fidèlement reproduites par le modèle de diffusion de la lumière basé sur l’optique physique. En revanche, le modèle basé sur les lois de l’optique géométrique ne parvient pas à produire des résultats satisfaisants.

Silver thin films are widely used in the glass industry for their insulation properties. Their stability is crucial. This work focus on silver solid-state dewetting (i.e. agglomeration) on amorphous silica substrates, divided into two axes: understanding the mechanisms thanks to in situ experiments and controlling the dewetting thanks to the patterning of the substrate at the nanoscale. The various in situ microscopy techniques revealed the role of specific grains in the dewetting mechanism. Dewetting proceeds into three steps: induction, propagation and sintering. Throughout these steps, the grains that eventually give birth to particles are identified, even as early as induction. Dewetting is strongly impacted by the oxygen content of the annealing atmosphere. When present, oxygen promotes the growth of very specific grains, where all dewetted material agglomerates. Without oxygen, silver is distributed on a larger number of grains, surrounding the holes that take a dendritic shape. A cautious image processing procedure allowed us to conclude that the capillary models usually invoked were not suitable for our system. A new model, based on the role of individual grains, is suggested. Dewetting on patterned substrates is a way to produce large arrays of organised nanoparticles. A method was developed to minimize in these arrays the number of defects inherent to dewetting. Optical measurements on such arrays showed that the spatial organisation of the particles led to a specific signature in optical absorption., Les couches minces d’argent sont largement employées dans l’industrie verrière à des fins d’isolation ; leur instabilité est un problème critique. Les travaux ont porté sur l’étude du démouillage (i.e. agglomération) de couches minces d’argent sur de la silice amorphe, selon deux axes : la compréhension du mécanisme par l’emploi de méthodes in situ et le contrôle du démouillage induit par une texturation du substrat à l’échelle nanométrique. Les différentes techniques de microscopie in situ ont permis de mettre en évidence le rôle particulier joué par certains grains lors du démouillage. Celui-ci se déroule en trois étapes distinctes : l’induction, la propagation, et le frittage. Les grains qui donnent lieu à des particules à la fin du démouillage sont identifiables durant toutes ces étapes. Le démouillage est fortement influencé par la présence d’oxygène dans l’atmosphère de recuit. En présence d’oxygène, certains grains très spécifiques accumulent la matière provenant du démouillage. En absence d’oxygène, l’argent se répartit sur davantage de grains, les trous adoptent une forme dendritique. Une analyse d’image a permis de montrer que le modèle capillaire usuellement employé dans la littérature ne permettait pas de décrire l’évolution constatée. Un nouveau modèle, fondé sur le rôle individuel des grains, a été proposé. Le démouillage sur des surfaces texturées permet d’obtenir des rangées de particules nanométriques organisées. Une méthode a été développée afin de minimiser les défauts intrinsèques à la méthode. Des mesures optiques effectuées sur ces échantillons ont mis en évidence une modification de l’absorption due à l’organisation spatiale des particules.

This work studies diffusive phenomena on glass surface functionalized with silicate thin films during thermal treatments. The temperature range extends from 550°C to 1050°C. In most cases diffusive phenomena between glass substrate and thin films stack can lead to a decrease of the properties of the active layers. Diffusive exchanges between a soda-lime flat glass and silica thin films (which can be doped with alumina), take place with two distinct kinetics. A fast migration of alkali ions from glass to silica is first observed, followed by a slow homogenization at the interface between the silica layer and the glass substrate due to the silica viscosity decrease. The key parameter which controls these two steps is the amount of aluminum in the silica layer. Indeed, the layer incorporates alkali ions in the form of charge compensator and network modifier in quantities depending linearly to the alumina content. Rather than limiting them systematically, these diffusive phenomena can also be controlled in order to obtain for example phase separation in these “thin film” geometries. For the silicate layers with SiO2-BaO-B2O3 compositions studied in this work, the morphology after phase separation and the kinetics of domains growth are influenced by similar parameters than in bulk glasses (such as temperature, composition, annealing duration, …) but also by surface energies which become non-negligible. In these confined systems, nucleation of phase separated domains occurs then preferentially at the interface with air and the thin film thickness influences directly the domains size., Ces travaux traitent de phénomènes diffusifs pouvant se dérouler à la surface de verres fonctionnalisés avec des couches minces de silicates lors de traitements thermiques. La gamme de température considérée s’étend de 550°C à 1050°C. Les échanges diffusifs entre le verre et l’empilement de couches minces conduisent souvent à une diminution des propriétés des couches actives. Les échanges entre un verre plat silico-sodocalcique et des couches minces de silice (pouvant être dopées alumine) se déroulent avec deux cinétiques distinctes. Une diffusion rapide des alcalins du verre vers la silice est observée dans un premier temps, conduisant ensuite à une homogénéisation plus lente entre le substrat et la couche, déclenchée par la diminution de la viscosité de la silice. Le paramètre clé contrôlant ces deux étapes est la quantité d’alumine présente dans la silice. En effet, la couche incorpore des alcalins sous forme de compensateur de charge et modificateur de réseau en quantités proportionnelles à la teneur en alumine. Plutôt que de les limiter, ces phénomènes diffusifs peuvent également être contrôlés pour obtenir par exemple de la séparation de phases dans ces géométries « couche mince ». Dans les couches de compositions SiO2-BaO-B2O3 étudiées, la morphologie après démixtion et la croissance des domaines sont pilotées d’une part par des paramètres similaires à ceux dans les verres massifs (température, composition, durée recuit, …) mais également par des énergies de surface qui deviennent non négligeables. La nucléation des phases dans ces systèmes confinés se fait alors préférentiellement en surface et l’épaisseur des couches à un impact direct sur la taille des domaines.

Author(s): Cebron, David; Le Bars, Michael; Le Gal, Patrice; Moutou, Claire; Leconte, Jeremy; Sauret, Alban

We investigate the mechanics of elastic fibres carrying liquid droplets. In such systems, buckling may localize inside the drop cavity if the fibre is thin enough. This so-called drop-on-coilable-fibre system exhibits a surprising liquid-like response under compression, and a solid-like response under tension. Here we analyze this unconventional behavior in further details and find theoretical, numerical and experimental evidences of negative stiffness events. We find that the first and main negative stiffness regime owes its existence to the transfer of capillary-stored energy into mechanical curvature energy. The following negative stiffness events are associated with changes in the coiling morphology of the fibre. Eventually coiling becomes tightly locked into an ordered phase where liquid and solid deformations coexist., 8 pages, 10 figures

International audience; A clue to understand wetting hysteresis on superhydrophobic surfaces is the relation between receding contact angle and surface textures. When the surface textures are large, there is a significant distribution of local contact angles around the drop. As seen from the cross section, the apparent contact angle oscillates as the triple line recedes. Our experiments demonstrate that the origin of these oscillations is a finite size effect. Combining side and bottom views of the drop, we take into account the 3D conformation of the surface near the edge to evaluate an intrinsic contact angle from the oscillations of the apparent contact angle. We find that for drops receding on axisymmetric textures the intrinsic receding contact angle is the minimum value of the oscillation while for a square lattice it is the maximum.

Gloss is a visual appearance attribute. It is a construction from the visual system built on the optical signal from a surface and sensed by the eye. Recent developments in fundamental spectrophotometry lead to instruments able to measure luminous reflection with an acuity equal to the visual system in terms of angular resolution and dynamic. A cross-discipline description between optics and vision is now possible on a same set of samples. In this work, we build through sol-gel process a metrological gloss scale. It is multivariate in terms of surface topology, refractive indices, hue and gloss levels. This scale is then characterized in roughness, specular gloss and BRDF. We expose the measurement techniques and corrections used on our goniospectrophotomer ConDOR. This instrument is dedicated to high resolution measurement of specular peaks. By the end of this study, Condor has reached an angular resolution of 0.014°, the smaller achieved until now, twice better than the human visual system acuity. The dynamic range extends over 6.5 decades. ConDOR is used to measure BRDF of several glossy samples from different scales. These measurements are studied and discussed. A first link between roughness and BRDF is drawn.Using a reference gloss scale, we finally study two aspects of gloss perception: both effects of a change in the solid angle of illumination and in the observation environment realism. Our results indicate that the visual system is more sensitive to gloss variations under realistic conditions as well in lighting as in environment. This effect is particularly noticeable on matt samples. Lesser realistic or lesser natural conditions could lead observers to confusion., Le brillant est un attribut de l'apparence visuelle. Il s'agit d'une construction du système visuel, basée sur le signal optique en provenance d’une surface et capté par l'œil. Les développements récents en spectrophotométrie fondamentale ont produit des instruments à même de mesurer la réflexion lumineuse avec une acuité égale à celle du système visuel humain. Une description transverse, visuelle et optique, d'un même ensemble d'échantillons est maintenant possible. Dans ce travail, nous construisons via des procédés sol-gel une échelle de brillant métrologique multivariée en termes de topologie de surface, indice de réfraction, teinte et niveaux de brillant. Cette échelle est caractérisée par la suite en rugosité, en indice de brillant spéculaire et en BRDF. Nous présentons les techniques de mesure et les corrections employées sur ConDOR, notre goniospectrophotomètre dédié à la mesure haute résolution du pic spéculaire. Au terme de cette étude, l'instrument présente une résolution angulaire de 0,014°, la meilleure résolution atteinte à ce jour, deux fois inférieure à celle du système visuel humain. La dynamique est de 6,5 décades. ConDOR est employé pour mesurer les BRDF de plusieurs échantillons brillants issus de différentes échelles. Elles sont étudiées et les discutées. Un premier lien entre rugosité et BRDF est esquissé. Nous étudions finalement en nous basant sur une échelle de référence de brillant deux aspects de sa perception : l’effet d'un changement d'angle solide d'illumination et l’effet du réalisme de l'environnement d'observation. Nos résultats montrent que le système visuel est plus sensible aux variations de brillant dans des conditions d'observations réalistes, tant en matière d'éclairage que d'environnement. L’effet est particulièrement prononcé pour les échantillons mats. Les conditions moins réalistes ou moins naturelles peuvent mener les observateurs à la confusion.

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.

In this document, I trace an account of my scientific trajectory so far, at the interface between liquids and solids. The manuscript is divided into four main parts, each exploring different aspects of highly unsteady hydrodynamical events or of interactions between elasticity and capillarity (with a hint of biology):1. Transient Jets2. Drop Impact3. Elasticity with Interfaces4. Capillary Spools

International audience; Superplastic deformation of a fully dense TZ3Y material, having a starting grain size around 135–145 nm and depleted of any amorphous phase at grain boundaries, has been investigated using compressive creep tests in air in the temperature range of 1100°–1300°C and the real stress range of 50–100 MPa. The key parameters of the creep law have been determined by performing temperature changes at a fixed stress and stress jumps at a fixed temperature. From such experiments, an average value for the apparent stress exponent of around 3 is obtained when the applied stress varied from 50 to 100 MPa and the temperature was kept constant in the range of 1100°–1300°C. The apparent activation energy of the mechanism controlling the creep deformation is evaluated at 577±75 kJ/mol in the temperature range of 1200°–1300°C, for a real stress of 70 MPa. The values of the apparent grain size exponent can be calculated from the initial grain size in the as-sintered samples and the grain size in the crept samples. In all cases, it was determined to be around 2. Observation of the microstructure of the crept samples, using scanning electron microscopy, reveals grain growth but does not show any significant elongation of the elemental grains. Transmission electron microscopy of a sample crept under 100 MPa at 1300°C reveals clear intragranular dislocation activity. This dislocation activity seems to be mainly confined in folds emitted at triple points. Because the creep parameters (experimental and calculated using a simple geometric model) and the microstructure observed are in good agreement, we propose that the creep mechanism involved is grain boundary sliding accommodated by dynamic grain growth and the formation of triple-point folds.

International audience; The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results.

We demonstrate a facile and scalable technique, rotational freezing, to produce porous tubular ceramic supports with radially aligned porosity. The method is based on a conventional ice-templating process in a rotatory mold and demonstrated here with yttria-stabilized zirconia (YSZ). We investigated the effects of solid loading, freezing temperature, and volume of the slurry on the microstructure, strength (o-ring test and four-point bending), and air permeability. The results show that pore volume and pore size can be controlled by the solid loading and freezing temperature respectively, and overall tube thickness can be adjusted by the volume of slurry initially poured into the mold. Decreasing pore size and pore volume increases the mechanical properties but decreases the air permeability. These tubes could be particularly interesting as tubular membrane supports such as oxygen transport membranes., Comment: 22 pages, 10 figures

Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity, and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses, we show that substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets on the softest substrates need over 70% more kinetic energy to splash than they do on rigid substrates. We show that this is due to energy losses caused by deformations of soft substrates during the first few microseconds of impact. We find that solids with Young’s moduli ≲ 100 kPa reduce splashing, in agreement with simple scaling arguments. Thus, materials like soft gels and elastomers can be used as simple coatings for effective splash prevention. Soft substrates also serve as a useful system for testing splash-formation theories and sheet-ejection mechanisms, as they allow the characteristics of ejection sheets to be controlled independently of the bulk impact dynamics of droplets., Physical Review Letters, 117 (18), ISSN:0031-9007, ISSN:1079-7114

Granular material flowing on complex topographies are ubiquitous in industrial and geophysical situations. In this paper, we study the small-scale experiment of a granular layer flowing on a rough incline. The shape of the granular front is solved analytically by using depth-averaged mass and momentum equations with a fractional expression for the frictional rheology μ(I), which is a generalization of Gray and Ancey [“Segregation, recirculation and deposition of coarse particles near two-dimensional avalanche fronts,” J. Fluid Mech. 629, 387 (2009)]. Unlike previous studies where a “plug flow dynamics” is assumed, a free shape factor α describing the vertical velocity profile is taken into account. The effect of inertia and shear rate on the front profile is evidenced through the introduction of the Froude number and the shape factor α. The analytical predictions are compared to experimental results published by Pouliquen [“On the shape of granular fronts down rough inclined planes,” Phys. Fluids 11, 1956 (1999)] and with our new experimental data obtained at higher Froude numbers. A good agreement between theory and experiments is found for α = 5/4, corresponding to a Bagnold-like velocity profile. However, we observe a systematic deviation near the head of the front where the height vanishes: the theory predicts a continuous precursor layer, while a grain-free region is observed experimentally. This suggests that the vertical velocity profile is not uniform inside the front, but the shape factor α tends to 1 near the head of the front. This raises questions about the vertical velocity profile in granular flows and about the expression of the rheological function μ(I) and its calibration from experimental data.

International audience; Although many tsunamis arise from underwater earthquakes, some are induced by submarine and subaerial landslides. For example, the collapse of an unstable cliff into the sea can generate a tsunami wave near the coast and exhibit extreme run-up. As a result, those tsunamis develop significant hazards to the population. The threat caused by such tsunamis strongly depends on the topography and location of the unstable cliff. Predicting the height of the tsunami wave generated by a subaerial or submarine collapse requires experimental investigations, analytical modeling and numerical simulations. In this chapter, we discuss recent experimental results on granular collapse in water and the influence of the physical parameters on the amplitude of the tsunami waves. We also present triphasic numerical simulations based on a finite-volumes method, where different rheologies are considered for the slide. We also emphasize the difficulty of such simulations and compare the numerical results to experimental measurements.

International audience; We report on the elastic modulus of 3D superlattices of single domain epsilon-Co nanocrystals self-assembled in face-centered cubic structures, so-called supracrystals. The effects of nanocrystal size, probe size, and supracrystal morphology on the elastic properties of supracrystals are investigated by nanoindentation measurements using an atomic force microscope. We show that elastic moduli of supracrystals of single domain epsilon-Co nanocrystals are invariant on varying the nanocrystal size and supracrystal morphology (films or faceted shape) produced through heterogeneous (solvent evaporation) growth process. A mechanical model is proposed to analyze elastic properties of supracrystals that differ from classical composite materials. These results are explained in terms of nanocrystallinity, that is, the crystalline structure of nanocrystals, which is a key parameter in achieving supracrystals of different nanocrystal sizes with robust elastic properties.

International audience; An implicit high order time (BDF) and polynomial degree discontinuous Galerkin (DG) level set method is presented in this talk. The major advantage of this new approach is an accurate mass conservation during the convection of the level set function, thanks to the implicit method. Numerical experiments are presented for the Zalesak and the Leveque test cases. The convergence rates versus time and space are investigated for both BDF and DG high orders. The capture of the zero level set interface is then improved by using an auto-adaptive mesh procedure. The problem is approximated by using the discontinuous Galerkin method for both the level set function, the velocity and the pressure fields.

International audience; Fiber-textured polycrystalline silicon thin films have demonstrated their interest as seed layers for the epitaxial growth of high-quality materials on substrates such as glass or plastics. In the present work, we report a comprehensive study of the aluminum-induced crystallization (AIC) of isolated Si domains. Our study not only demonstrates the fabrication by AIC of shape- and size-controlled Si monocrystals at the nanoscale but also allows for the prediction of minimal annealing conditions for complete crystallization of such structures. These ultrathin [111]-oriented monocrystals are promising candidates as selected-area epitaxy substrates with both an easy control on the morphology of these structures and a low-temperature fabrication process.

International audience; We investigate the equilibrium morphology of a finite volume of liquid placed on two parallel rigid fibers of different radii. As observed for identical radii fibers, the liquid is either in a column morphology or adopts a drop shape depending on the inter-fiber distance. However the cross-sectional area and the critical inter-fiber distance at which the transition occurs are both modified by the polydispersity of the fibers. Using energy considerations, we analytically predict the critical inter-fiber distance corresponding to the transition between the column and the drop morphologies occurs. This distance depends both on the radii of the fibers and on the contact angle of the liquid. We perform experiments using a perfectly wetting liquid on two parallel nylon fibers: the results are in good agreement with our analytical model. The morphology of the capillary bridges between fibers of different radii is relevant to the modeling of large arrays of polydisperse fibers.

International audience

High strength and high toughness are usually mutually exclusive in engineering materials. Improving the toughness of strong but brittle materials like ceramics thus relies on the introduction of a metallic or polymeric ductile phase to dissipate energy, which conversely decreases the strength, stiffness, and the ability to operate at high temperature. In many natural materials, toughness is achieved through a combination of multiple mechanisms operating at different length scales but such structures have been extremely difficult to replicate. Building upon such biological structures, we demonstrate a simple approach that yields bulk ceramics characterized by a unique combination of high strength (470 MPa), high toughness (22 MPa.m1/2), and high stiffness (290 GPa) without the assistance of a ductile phase. Because only mineral constituents were used, this material retains its mechanical properties at high temperature (600{\deg}C). The bioinspired, material-independent design presented here is a specific but relevant example of a strong, tough, and stiff material, in great need for structural, transportations, and energy-related applications., Comment: 27 pages, 4 figures, supplementary data, 47 references

International audience; Liquid may give strong cohesion properties to a granular medium, and confer a solid-like behavior. We study the erosion of a fixed circular aggregate of wet granular matter subjected to a flow of dry grains inside a half-filled rotating drum. During the rotation, the dry grains flow around the fixed obstacle. We show that its diameter decreases linearly with time for low liquid content, as wet grains are pulled-out of the aggregate. This erosion phenomenon is governed by the properties of the liquids. The erosion rate decreases exponentially with the surface tension while it depends on the viscosity to the power -1. We propose a model based on the force fluctuations arising inside the flow, explaining both dependencies: the capillary force acts as a threshold and the viscosity controls the erosion time scale. We also provide experiments using different flowing grains confirming our model.

Colloque avec actes et comité de lecture. Internationale.; International audience; L’addition de liquide dans un milieu granulaire peut lui conférer une cohésion importante, et lui permettre de se comporter comme un substrat solide. Un milieu hétérogène contenant du liquide présentera donc plusieurs phases de natures différentes. L’interaction entre phase sèche et humide donne lieu à des échanges, arrachements de grains à la phase humide, ou agglomération de grains initialement secs. Ces échanges peuvent aboutir à des changements de morphologie des domaines. Nous avons mis en place une expérience d’érosion d’un tas humide cohésif dans une cellule mince, entre deux plaques de verre. L’écoulement de grains secs apportés à débit constant produit l’érosion du milieu humide par l’arrachement régulier de grains au tas. Nous avons pu observer la déstabilisation d’une interface initialement plane. Le couplage entre la contrainte de l’écoulement et la forme du tas crée des structures en forme de marches se propageant vers l’amont par l’érosion. Les propriétés de ces marches (taille, vitesse de propagation…) dépendent notamment de la pente du tas formé.

National audience; L’intérêt grandissant pour l’utilisation des fluides supercritiques appliqués à la synthèse de matériaux inorganique repose sur la volonté de développer de nouveaux procédés continus pour la production de nanopoudres. Le procédé semi-continu PCA (Precipitation with Compressed Anti-solvent) couplantl’utilisation du CO2supercritique (CO2SC) comme antisolvant avec des réactions chimiques de type sol-gel (hydrolyse/condensation) a été développé dans notre équipe. La mise en œuvre de ce procédé pour la synthèse de zircone yttriée, stabilisée en phase tétragonale (SC-3Y-TZP) ou cubique (SC-YSZ), a rendu possible le contrôle de la morphologie, ainsi que de la structure et de la microstructure de ces poudres. L’influence des paramètres de préparation des sols et d’hydrodynamique du réacteur sur les caractéristiques des poudres a notamment été mise en évidence. Les poudres aux caractéristiques optimisées, obtenues à 350°C et 30MPa, sont constituées de particules de taille nanométriques (50 à 130 nm de diamètre) présentant une sous structure nanophasée (cristallites de 5-7 nm). Ces caractéristiques ont pour conséquence une densité apparente très faible (~0.1g/cm3) et une surface spécifique élevée (jusqu’à 195 m2/g). Le comportement au frittage de ces poudres a été caractérisé. Un frittage multi-étapes, commençant à basse température (400°C), due à la structure multi-échelles et mésoporeuse des particules, a été mis en évidence. La densification de ces poudres a été étudiée par frittage SPS (Spark Plasma Sintering). Cette étude a montré une très grande réactivité au frittage des poudres nanométriques préparées par voie sol-gel assistée CO2SC, qui se traduit par une densification élevée dumatériau céramique final (99.9%), tout en maintenant une taille de grain nanométrique (80nm)

International audience

International audience; We study experimentally the distribution of local stresses in a granular material confined inside a vertical cylinder. We use an image correlation technique to measure the displacement field of the container induced by the forces exerted by the grains on the inner wall. We describe an optimization procedure based on the linear theory of elastic shells to deduce the distribution of these forces from the measured displacement field. They correspond to the stress field of the granular material close to the container's inner wall. We first confirm the validity of Janssen's description for various experiments, including the influence of the bead diameter and the effect of an additional mass on top of the granular column. We then apply this method to determine the stress field during the gravity-driven discharge of a silo through an aperture.

International audience; The control of the growth morphologies of ice crystals is a critical issue in fields as diverse as biomineralization, medicine, biology, civil or food engineering. Such control can be achieved through the ice-shaping properties of specific compounds. The development of synthetic ice-shaping compounds is inspired by the natural occurrence of such properties exhibited by antifreeze proteins. We reveal how a particular zirconium acetate complex is exhibiting ice-shaping properties very similar to that of antifreeze proteins, albeit being a radically different compound. We use these properties as a bioinspired approach to template unique faceted pores in cellular materials. These results suggest that ice-structuring properties are not exclusive to long organic molecules and should broaden the field of investigations and applications of such substances.

International audience

et al., Alumina-zirconia nano-composites were recently developed as alternative bearing materials for orthopedics. Previous, preliminary reports show that such alumina-zirconia nanocomposites exhibit high crack resistance and low wear rate. In this paper, additional information is given in terms of wear, crack resistance and ageing behaviour: femoral heads are inspected after 7 million cycles of wear testing on a hip simulator, crack resistance is measured and compared to other ceramics used today in orthopedics, slow crack growth is reported under static and cyclic fatigue, and aging resistance is assessed. We also report on the load to failure of femoral heads prototypes during compression tests. This overall reliability assessment ensures a potential future development for these kinds of new nanocomposites in the orthopedic field. © 2010 Elsevier Ltd.

International audience; This work started as part of an investigation into the mechanisms by which fine zirconia aqueous dispersions can be processed for ceramic materials engineering. Aqueous dispersions of TZ3Y fine zirconia particles obtained by dispersion of dry powder in acidic solutions (pH 3) have been subjected to compression through osmotic experiments. The results show a behavior that is unusual when compared with the classical behavior of colloidal dispersions. Indeed, the 50 nm particles are well dispersed and protected from aggregation by electrical double layers, with a high zeta potential (60–80 mV). Yet, during osmotic compression, the dispersion goes from a liquid state to a gel state at a rather low volume fraction, φ=0.2, whereas the liquid–solid transition for repelling particles is expected to occur only at φ=0.5. This early transition to a state in which the dispersion does not flow may be a severe drawback in some uses of these dispersions, and thus it is important to understand its causes. A possible cause of this early aggregation is the presence of a population of very small particles, which are seen in osmotic stress experiments and in light scattering. We propose that aggregation could result from the compression of this population, through either of the following mechanisms: (a) An increase in pressure causes the small particles to aggregate with each other and with the larger ones or (b) An increase in pressure induces a depletion flocculation phenomenon, in which the large particles are pushed together by the smaller ones.

National audience; Granular media represent a remarkable example of materials endowed with a discrete structure in which steric exclusions and topological disorder (grain connectivity through a network of intergrain contacts) are fundamental for rheology. We propose a general framework for investigating this link between microstructure and plastic behavior in the case of a granular material composed of rigid grains at quasistatic equilibrium. We discuss the nature of microstructural variables and we show that setric exclusions and the equilibrium condition lead to a domain of accessible states in the phase space. The results are compared to numerical simulations.

National audience; It is proposed to identify damage variables and their growth with loading in two dimensions by only using full-field displacement measurements. The equilibrium gap method is used to estimate the damage field during a biaxial experiment on a sample made of a composite material. From the analysis of a sequence of measurements, a proposed form of constitutive law is tested and identified.; Il est proposé d’identifier des variables d’endommagement et leur évolution avec un chargement en deux dimensions en utilisant uniquement des champs de déplacement. La méthode d’écart à l’équilibre permet d’estimer un champ d’endommagement durant un essai biaxial sur un composite. A partir de l’analyse d’une séquence de mesures, une loi d’évolution est proposée et identifiée.

A ceramic membrane with an ordered mesoporous top layer has been developed. The active layer possesses a close-packed hexagonal network of spherical pores. Results on permeation of helium and argon through the membrane are presented and correlated with the structural and textural properties of the top layer. New insights are given on the porosity of this close-packed hexagonal structure.

International audience; Tracer dispersion is studied in an open crack where the two rough crack faces have been translated with respect to each other. The different dispersion regimes encountered in rough-wall Hele-Shaw cell are first introduced, and the geometric dispersion regime in the case of self-affine crack surfaces is treated in detail through perturbation analysis. It is shown that a line of tracer is progressively wrinkled into a self-affine curve with an exponent equal to that of the crack surface.This leads to a global dispersion coefficient which depends on the distance from the tracer inlet, but which is still proportional to the mean advection velocity. Besides, the tracer front is subjected to a local dispersion (as could be revealed by point measurements or echo experiments) very different from the global one. The expression of this anomalous local dispersion coefficient is also obtained.

International audience; The in situ elastic and plastic behaviors of sodium aluminosilicate glasses with different degrees of depolymerization were analyzed using Brillouin spectroscopy. The observed elastic anomaly progressively vanished with depolymerization. The densification process appears to be different from that observed in pure silica glass. In the plastic regime of densified glasses hysteresis loops were observed and related to modification of the local silicon environment facilitated by the addition of sodium.

International audience; Two‐dimensional spatial distributions and growths of nucleated bubbles during the re‐melting of “float” glass samples are experimentally investigated. To follow the bubble population undergoing coalescence, the temporal behavior of the Voronoï tessellation built by the bubble positions are monitored. During coalescence, the Voronoï cell areas are fitted by a single‐parameter Gamma distribution. Numerical time simulation of population of bubbles undergoing coalescence shows an exponential increase in the parameter associated to the Gamma distribution with the fraction of coalesced bubbles in agreement with experimental observation. An initial density of nuclei is then estimated; direct observation would require an extremely high space resolution. The bubble number density is two orders of magnitude larger on the side which was in contact with tin bath than on the other side in contact with atmosphere. Moreover, bubbles grow faster on tin side. From a thermodynamic and mass transfer models, we prove that tin reduces the glass former liquid which leads to an increase in dissolved sulfur explaining the more abundant bubble population and the enhanced growth rate on tin side.