HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
Not a member yet
13939 research outputs found
Sort by
Toward vanishing droplet friction on repellent surfaces
No full textInternational audienceSuperhydrophobic surfaces are often seen as frictionless materials, on which water is highly mobile. Understanding the nature of friction for such water-repellent systems is central to further minimize resistance to motion and energy loss in applications. For slowly moving drops, contact-line friction has been generally considered dominant on slippery superhydrophobic surfaces. Here, we show that this general rule applies only at very low speed. Using a micropipette force sensor in an oscillating mode, we measure the friction of water drops approaching or even equaling zero contact-line friction. We evidence that dissipation then mainly stems from the viscous shearing of the air film (plastron) trapped under the liquid. Because this force is velocity dependent, it can become a serious drag on surfaces that look highly slippery from quasi-static tests. The plastron thickness is found to be the key parameter that enables the control of this special friction, which is useful information for designing the next generation of ultraslippery water-repellent coatings
A Novel Ti12-based Metal-Organic Framework for Photocatalytic Hydrogen Evolution
No full textInternational audienceConstructing titanium-based metal-organic frameworks (Ti-MOFs) is an effective way towards upgrading TiOx and the enhancement of their photocatalytic performance throughout higher accessibility to active sites and better tunability of photophysical properties. In this regard, Ti-MOFs have attracted much attention as photocatalyst candidates owing to their porosity and tunability in terms of chemical composition and pore engineering. However, Ti-MOFs remain still one of the least developed sub-class of MOF materials because of the complexity of titanium chemistry in solution hampering their rational design, despite recent progresses. Here, we present a new microporous Ti-MOFs with acs topology, labeled MIP-209(Ti) (MIP stands for Materials from Institute of Porous Materials of Paris) constructed by a nitro terephthalate ligand and Ti12O15 oxo-clusters, as revealed by continuous rotation electron diffraction (cRED). MIP-209(Ti) can be obtained using various terephthalate (1,4-BDC2-) derivatives such as NO2-BDC and 2Cl-BDC using an eco-friendly solvent, suggesting the ability of Ti12-MOFs for isostructural chemistry. Alternatively, it is also possible to tune the composition of its Ti-oxo-cluster, similarly to MIP-177(Ti)-LT bearing the same Ti12O15 sub-unit. Typically, low percentage Cr3+ doping (≤ 5 at%) in MIP-209(Ti) favorably enhances the water stability. Interestingly, photocatalytic hydrogen evolution from water splitting reaction (HER) were measured for MIP-209(Ti-Cr)-NO2 and a significant hydrogen production rate, with good reusability and stability under simulated solar light irradiation, were revealed. It showed enhanced photocatalytic hydrogen production performances under simulated solar light irradiation compared to the benchmark Ti-MOF IEF-11 with a fourfold enhanced hydrogen production in HER in 5h in presence of methanol (5812 µmol of H2/gcat against 1391 µmol of H2/gcat) as well as, without any noble metal co-catalyst, a 6-fold enhanced overall water splitting production (681 and 325 µmol/gcat of H2 and O2, respectively for MIP-209, against 94 and 53 µmol/gcat of H2 and O2, respectively, for IEF-11). This work represents a leap forward in the synthesis of Ti-MOFs and their practical photocatalytic applications
Tuning the BCS-BEC crossover of electron-hole pairing with pressure
No full textInternational audienceIn graphite, a moderate magnetic field confines electrons and holes into their lowest Landau levels. In the extreme quantum limit, two insulating states with a dome-like field dependence of the their critical temperatures are induced by the magnetic field. Here, we study the evolution of the first dome (below 60 T) under hydrostatic pressure up to 1.7 GPa. With increasing pressure, the field-temperature phase boundary shifts towards higher magnetic fields, yet the maximum critical temperature remains unchanged. According to our fermiology data, pressure amplifies the density and the in-plane effective cyclotron mass of hole-like and electron-like carriers. Thanks to this information, we verify the persistent relevance of the BCS relation between the critical temperature and the density of states in the weak-coupling boundary of the dome. In contrast, the strong-coupling summit of the dome does not show any detectable change with pressure. We argue that this is because the out-of-plane BCS coherence length approaches the interplane distance that shows little change with pressure. Thus, the BCS-BEC crossover is tunable by magnetic field and pressure, but with a locked summit
Formation of 3-Alkynylidenephthalides by Gold(I)-Catalyzed Alkynylative Cyclization of o-Alkynylbenzoic Acids under Visible Light Irradiation
No full textInternational audienceHerein, we report a Csp 2 -Csp cross-coupling process involving the merger of gold catalysis and visible light photocatalysis leading to the alkynylative cyclization of o-alkynyl benzoic acids. The corresponding and previously undescribed alkynylidenephthalide products were obtained as mixtures of E:Z isomers. The key C-C bond formation is based on the photoactivation of the oxidative addition of an alkynyliodide to a vinylgold(I) intermediate resulting from an initial 5-exo-dig cyclization pathway, as supported by mechanistic studies including DFT calculations
MOF‐Enhanced Phototherapeutic Wound Dressings Against Drug‐Resistant Bacteria
No full textInternational audiencePhototherapy is a low‐risk alternative to traditional antibiotics against drug‐resistant bacterial infections. However, optimizing phototherapy agents, refining treatment conditions, and addressing misuse of agents, remain a formidable challenge. This study introduces a novel concept leveraging the unique customizability of metal–organic frameworks (MOFs) to house size‐matched dye molecules in “single rooms”. The mesoporous iron(III) carboxylate nanoMOF, MIL‐100(Fe), and the hydrophobic heptamethine cyanine photothermal dye (Cy7), IR775, are selected as model systems. Their combination is predicted to minimize dye–dye interactions, leading to exceptional photostability and efficient light‐to‐heat conversion. Furthermore, MIL‐100(Fe) preserves the antimicrobial nature of hydrophobic IR775, enabling it to disrupt bacterial cell envelopes. Through electrospinning, MIL‐100(Fe)@IR775 nanoparticles are shaped into a gelatin‐based film dressing for the treatment of skin wounds infected by Methicillin‐resistant Staphylococcus aureus (MRSA). Activation of the dressing requires only a portable near‐infrared light‐emitting diode (NIR LED) and induces both low‐dose photodynamic therapy (LPDT) and mild‐temperature photothermal therapy (MPTT). Combined with the antimicrobial properties of IR775 and ferroptosis‐like lipid peroxidation induced by MIL‐100(Fe), the photoactive dressing eradicates MRSA and the healing is as quick as the uninfected wounds. This safe, cost‐effective, and multifunctional therapeutic wound dressing offers a promising solution to overcome the current bottleneck in phototherapy
Comportement aérodynamique et impact de la propulsion instationnaire, application à la voile de compétition
No full textThis experimental thesis is part of a project to improve sports performance in Olympic sailing. The work focused on the iQFoil windsurf series and the Formula Kite kitefoil series. Aerodynamic drag forces are dominant in these Olympic foil series. This work therefore focuses on the aerodynamic characterisation of the various parts of the iQFoil and Formula Kite boats (except the kite sail) as well as the impact of the athletes. Finally, the phenomenon of unsteady propulsion called 'pumping' used by windsurfers is studied. Initially, the work studies the various parts of the craft that play a role in aerodynamic performance. Measurements are carried out on a scale of 1 in the wind tunnels of the Institut AéroTechnique of Saint-Cyr l'Ecole. They cover the boards and the complete sail rig, as well as the athletes' positions and equipment. We designed the various experimental measurement devices. The sail rigging was studied on a scale of 1 in order to take account of the interactions between the flow and the rigging. We are studying the influence of sail settings and flow speed on the deformation of the sail and its shape in three dimensions using a photogrammetry device that we have developed. Finally, the impact of sail deformation on aerodynamic performance is studied. Secondly, we look at a technique used by windsurfers to generate unsteady propulsion. During race starts or in light wind conditions, in particular after manoeuvres such as tacking, athletes use a technique called "pumping" to initiate or maintain the boat's flight. This involves periodically varying the angle of incidence of the sail relative to the wind, providing intermittent propulsion to keep the board above the water. The aim of our work is to characterise and optimise the unsteady forces generated by the pitching movement, which is a simplified version of "pumping". In particular, the effect of the mean angle of incidence on the generation of unsteady forces is discussed. A comparison between a symmetrical airfoil and a rigid sail shape highlights differences in the dominant kinematic parameters of this unsteady effect and in the generation of forces.Cette thèse expérimentale s'inscrit dans un projet pour la performance sportive en voile olympique. Ce travail a porté sur la série de planche à voile, iQFoil et sur la série de kitefoil, Formula Kite. Les efforts aérodynamiques traînants sont dominants pour ces séries olympiques à foil. Ce travail s'intéresse donc à la caractérisation aérodynamique des différentes parties des embarcations iQFoil et Formula Kite (sauf le parachute) ainsi que l'impact des athlètes. Enfin le phénomène de propulsion instationnaire appelé "pumping" utilisé par les véliplanchistes est étudié. Dans un premier temps, les travaux menés étudient les différentes parties des embarcations qui jouent un rôle dans la performance aérodynamique. Les mesures sont réalisées à l'échelle 1 dans les souffleries de l'Institut AéroTechnique de Saint-Cyr l'Ecole. Elles portent sur les flotteurs et le gréement complet de voile ainsi que sur les positions et les équipements des athlètes. Nous avons conçu les différents dispositifs expérimentaux de mesures. Le gréement de voile a été étudié à l'échelle 1 afin de rendre compte des interactions entre l'écoulement et celui-ci. Nous étudions l'influence des réglages de la voile et de la vitesse de l'écoulement sur la déformation de la voile et sa forme en trois dimensions grâce à un dispositif de photogrammétrie que nous avons mis au point. Enfin, l'impact de la déformation de la voile sur les performances aérodynamique a été étudié. Dans un second temps, nous nous intéressons à une technique utilisée par les véliplanchistes permettant de générer de la propulsion instationnaire. En effet, lors des départs de course ou dans des conditions de vent faible, en particulier après des manœuvres telles que le virement de bord, les athlètes utilisent une technique appelée "pumping" pour initier ou maintenir le vol de l'embarcation. Cela consiste à faire varier périodiquement l'angle d'incidence de la voile par rapport au vent, fournissant une propulsion intermittente pour maintenir la planche en l'air. Notre travail vise à caractériser et à optimiser les forces instationnaires générées par le mouvement de "pitching" qui est un mouvement simplifié. En particulier, l'effet de l'angle d'incidence sur la génération des forces instationnaires est discuté. Une comparaison entre un profil aérodynamique symétrique et une forme de voile, rigides, met en lumière des différences sur les paramètres cinématiques dominants de cet effet instationnaire ainsi que sur la génération des forces
Modélisation de la diffusion multiple et dynamique de la lumière dans un éjecta issu d’un choc
No full textIn this doctoral thesis, we aim to model the spectrograms of the optical diagnostic named Photon Doppler Velocimetry (PDV) in the context of characterizing ejecta from shock experiments on metals. To do this, we first establish the link between the PDV spectrogram and a common quantity in statistical optics, the specific intensity. This specific intensity is classically governed by a Radiative Transfer Equation (RTE), which, in the context of this thesis, has been modified to account for the dynamic and statistically inhomogeneous nature of an ejecta. The numerical resolution of this equation using a Monte Carlo scheme allowed us to retrieve, through simulation, the main characteristics of the PDV spectrograms of ejecta and to highlight the importance of multiple scattering. Building on this result, we explore the sensitivity of PDV spectrograms to various parameters such as wavelength, particle size-velocity distribution, and its statistical inhomogeneity. We also study the possibility of quantitatively modeling spectrograms using a simpler approach based on a diffusion equation valid in the regime of very strong scattering. We prove the relevance of this approximation in many regimes, but the inhomogeneity and anisotropy of the velocity distribution of an ejecta render it inadequate. Finally, we explore the impact on PDV spectrograms of the presence of anisotropic objects near the free surface of the metal. We show, using a very simple model, that the presence of these objects substantially modifies the spectrograms, and our study tends to prove that they are the cause of a well-known dip in the spectrograms observed by experimenters.Dans cette thèse de doctorat, nous visons à modéliser les spectrogrammes du diagnostic optique de Vélocimétrie Hétérodyne (VH) dans le cadre de la caractérisation des éjectas issus d’expériences de choc sur des métaux. Pour cela, nous établissons d’abord le lien entre le spectrogramme VH et une quantité usuelle en optique statistique, la luminance. Cette luminance est classiquement régie par une Équation de Transfert Radiatif (ETR) qui, dans le cadre de cette thèse, a été adaptée pour rendre compte de l’aspect dynamique et statistiquement inhomogène d’un éjecta. La résolution numérique de cette équation par méthode de Monte Carlo a permis de retrouver par simulation les principales caractéristiques des spectrogrammes VH d’éjectas et de mettre en avant l’importance de la diffusion multiple. Fort de ce résultat, nous explorons la sensibilité des spectrogrammes VH à différents paramètres comme la longueur d’onde, la distribution taille-vitesse des particules et son inhomogénéité statistique. Nous étudions également la possibilité de modéliser quantitativement les spectrogrammes à partir d’une approche plus simple basée sur une équation de diffusion valide en régime de très forte diffusion. Nous prouvons la pertinence de cette approximation dans de nombreux régimes mais l’inhomogénéité et l’anisotropie de la distribution en vitesse d’un éjecta la mettent en défaut. Enfin, nous explorons l’impact sur les spectrogrammes VH de la présence d’objets anisotropes proches de la surface libre du métal. Nous montrons à partir d’un modèle très simple que la présence de ces objets modifie de manière substantielle les spectrogrammes et notre étude tend à prouver qu’ils sont à l’origine de l’apparition d’un creux bien connu des expérimentateurs dans les spectrogrammes
Étude du bouchage de milieux poreux par des agrégats huile-solides
No full textThe study of porous media clogging is of interest in various fields, such as oil extraction or water treatment. The literature generally focuses on clogging caused by oil only or solid particles only. However, when these two elements are injected simultaneously, they can form complex aggregates, such as Pickering emulsions or capillary suspensions. These structures exhibit specific interactions and additional interfacial forces, making their behavior in porous media more difficult to describe and model. In the context of Produced Water ReInjection (PWRI), this type of plugging is generally more severe, leading to significant injectivity losses and additional costs. The aim of this thesis is to improve the understanding of clogging mechanisms during this co-injection. Using micro- and millifluidic devices, it has been possible to couple pressure drop measurements with optical observations and study clogging on several scales. In two-dimensional model media, consisting of a series of parallel identical pores, the injection of oil and particles leads to the formation of plugs within the constrictions. They mainly form at the ends of these narrow areas (inlet and outlet), over a length comparable to their width. We highlight the major role played by this damage, in the overall permeability loss, which eventually reaches a steady state. We associate this regime with a dynamic equilibrium between accumulation and erosion of the suspended objects. Accumulation occurs by successive individual deposition, while erosion happens by detachment of larger fragments. In more complex model porous media, we show that damage remains localized at the inlet, over a short distance. This particularly dense zone has been identified, similarly to 2D experiments, as the main cause of injectivity loss. Because of this erosion, we reveal that unclogging by clean water injection is possible. It leads to a channeling phenomenon, accompanied by partial permeability recovery. These results open up perspectives for optimizing prevention techniques or improving unclogging strategies.L’étude du bouchage des milieux poreux présente un intérêt dans de nombreux domaines, tels que la récupération des hydrocarbures ou le traitement des eaux. La littérature se concentre généralement sur le colmatage causé par de l’huile seule ou des particules solides seules. Cependant, lorsque ces deux éléments sont injectés simultanément, ils peuvent former des agrégats complexes, comme des émulsions de Pickering ou des suspensions capillaires. Ces structures présentent des interactions spécifiques et des forces interfaciales complexes, rendant leur comportement dans les milieux poreux plus difficile à décrire et à modéliser. Dans le contexte de réinjection des eaux de production (PWRI), ce type de colmatage est généralement plus sévère, engendrant d’importantes pertes d’injectivité et des coûts supplémentaires. L’objectif de cette thèse est d’améliorer la compréhension des mécanismes de bouchage lors de cette injection simultanée. Grâce à des dispositifs micro- et millifluidiques, il a été possible de coupler les mesures de perte de charge avec les observations optiques et d’étudier le colmatage à plusieurs échelles. Dans des milieux modèles en deux dimensions, composés d’une série de pores identiques en parallèle, l’injection d’huile et de particules entraîne la formation de bouchons au sein des constrictions. Ils se forment en particulier aux extrémités de ces zones étroites (amont et aval), sur une longueur comparable à leur largeur. Nous mettons en évidence le rôle majeur de ces dernières dans la perte de perméabilité globale, qui finit par atteindre un état stationnaire. Nous associons ce régime à un équilibre dynamique entre un phénomène d’accumulation et d’érosion des objets en suspension. L’accumulation se fait par dépôt individuel successif, tandis que l’érosion survient par détachement de fragments. Dans des milieux poreux modèle plus complexes, nous montrons que l’endommagement reste localisé à l’entrée, sur une courte distance. Cette zone particulièrement dense a été identifiée, de manière similaire aux expériences 2D, comme étant la principale cause de perte d’injectivité. En raison de cette érosion, nous révélons que le décolmatage par injection d’eau propre est possible. Elle entraine la formation de chemins préférentiels d’écoulement, accompagnée d’une récupération partielle de la perméabilité. Ces résultats ouvrent des perspectives pour l’optimisation des techniques de prévention ou d’amélioration des stratégies de débouchage
Single polyoxometalate-based nanoclusters characterized by infrared absorption nanospectroscopy
No full textInternational audienceBottom-up engineering is a very attractive field. However, the periodic organization of molecules on a solid substrate is challenging, particularly in the selection of the appropriate characterization technique which is suitable for both large area and accurate analysis at the nanoscale. Here, this study demonstrates the unambiguous identification of complex molecular layers by infrared absorption microscopy at the nanometric scale. This technique allowed for the direct observation of the presence of isolated polyoxometalate-based nanoclusters dispersed all over a substrate