HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Tuning bubble coalescence rates over orders of magnitude in liquid mixtures of simple surface rheology : experiments and theory
No full textThe coalescence time of bubbles in a liquid depends both on the nature of the liquid, which determines the molecular interactions between the gas/liquid interfaces and their surface rheology, and on the geometry, prescribed by the curvature of the bubbles. Coalescence is well described in pure liquids that have no interfacial rheology and in which the interactions are attractive. In contrast, the mechanisms are poorly understood in more complex liquids in which coalescence times are orders of magnitudes larger than in pure liquids and are unpredictable. To provide insight on these mechanisms, we use model systems that are binary mixtures of miscible oils. In these liquids, interfaces have purely attractive molecular interactions and the surface rheology simply reduces to a well-described surface elasticity, which can be controlled by the composition of the mixture. We measure the coalescence rate by forming periodic trains of bubbles in millifluidic tubes whose radius varies over 1.5 decade. We report coalescence times spanning more than three decades and, for a given composition, varying according to a power law with curvature, with an exponent larger than that reported in pure liquids. The experimental behavior is in excellent agreement with a numerical resolution of the coupled thermodynamical and hydrodynamical equations, performed in the simple geometry of a suspended liquid film. Our results clearly reveal the effects of both geometry and surface elasticity and show, for the first time, how the coalescence time of bubbles in liquid mixtures can be predicted quantitatively
Ni-exsolved catalysts from hard templated mesoporous LaNiO3 perovskite for highly efficient NH3 decomposition
No full textInternational audienceLaNiO3 perovskites have been recently studied for H2 production from NH3 decomposition / cracking. So far, this material has had its catalytic performance boosted along the addition of basic doping agents. Nevertheless, little attention has been paid to the potential benefit to gain from its textural properties. In this work, high specific surface area LaNiO3 were prepared through the yet never explored combination of citric acid as complexing agent, SBA-15 as sacrificial hard template (to create mesopores), and exsolution (to expose and activate Ni). After removal of the template, the resulting mesoporous LaNiO3 reached a specific surface area as high as 200 m2/g. In a second step, Ni nanoparticles were exsolved to reach the final catalyst, yielding 89 % NH3 conversion at 550 °C and a GHSV of 30 000 mL/gcata.h, with a stability of at least 72 h. Due to the extended specific surface area of LaNiO3, exsolved Ni nanoparticles were highly dispersed which greatly enhanced the catalytic performance. This catalyst achieved a H2 formation rate of 29 mmol/gcata.min which is higher than any previously reported doped LaNiO3. This work demonstrates the feasibility to produce both noble metal and promoter-free LaNiO3 being particularly active and stable in efficient H2 production from NH3 decomposition
A Remarkable Catalyst-Free Photochemical Alkene Hydrophosphination with Bis(trimethylsilyl)phosphonite
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Unlocking the scale-up of the benchmark MOFs MIL-53(Al)’s
No full textEnvironment-friendly synthesis of metal-organic frameworks (MOFs) is crucial to meet growing industrial demand. Here, we present a generalized and scalable route for the production of the prototypical Al-OH chain-based microporous and flexible MIL-53 (MIL = Materials Institut Lavoisier) with various functional groups (X = -H, ˗NH2, ˗NO2, -OH, -COOH)). Until recently, the scale-up of these robust and cost-effective Al-MOFs was hindered by challenges associated with their synthesis and purification, restricting their practical deployment. In this work, we optimized a reflux-based aqueous synthesis method to yield either nano-sized or micron-sized particles. Additionally, we developed a novel, rapid and ambient-pressure exchange process using green solvents to efficiently remove residual free linkers from the MOF pores. This approach affords high-purity MOFs and enables large-scale production with a high space-time yield (ca. 200 kg/m³/day), paving the way for broader implementation. As a proof of concept, we successfully produced MIL-53(Al)-NH2 up to 300g scale maintaining high crystalline quality and adsorption properties comparable to those achieved at smaller scale. Finally, spherical beads of MIL-53(Al)-NH₂ were fabricated using bentonite as binder. These beads exhibited excellent mechanical strength, while retaining their CO₂ adsorption performance, as evidenced by both single-component adsorption isotherms and dynamic breakthrough experiments
Astroglial regulation of critical period plasticity in the developing brain
No full textInternational audienceAstrocytes emerge as pivotal regulators of brain plasticity during critical periods (CPs) of development. Beyond their traditional roles in supporting neuronal function, astrocytes actively shape synaptic circuits maturation and remodeling during postnatal experience-dependent plasticity. Through mechanisms such as regulation of the extracellular matrix or synaptic pruning, astrocytes influence the timing and extent of plasticity across sensory and cognitive systems. These processes have been demonstrated in various animal models and forms of plasticity, indicating that these glial cells play a conserved role across species. Such findings unveil the dynamic and central role of astrocytes in coordinating the complex interplay between neural circuits and external stimuli during critical windows of brain development
The trade-off between growth and risk in Kelly’s gambling and beyond
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Excited State Transient Phenomena in Two Different Phases of the Photoactive MOF MIP‐177(Ti)
No full textInternational audienceAbstract The metal organic framework (MOF) MIP‐177(Ti) is under the spotlight for its robust photo‐response and stability. This MOF can be synthesized in forms: MIP‐177(Ti)‐LT (LT: low temperature) and MIP‐177(Ti)‐HT (HT: high temperature). The MIP‐177(Ti)‐LT version comprises of Ti 12 O 15 units interconnected by 3,3′,5,5′‐tetracarboxydiphenylmethane (mdip) ligands and interconnecting formate groups. Upon high temperature treatment, MIP‐177(Ti)‐LT loses its formate groups, thus rearranging into a continuous 1‐D chain of Ti 6 O 9 units leading to the MIP‐177(Ti)‐HT. Based on this 1‐D connected structure, one should expect a higher catalytic activity of MIP‐177(Ti)‐HT. Nevertheless, the hydrogen evolution reaction photoactivity assessment clearly indicates the opposite. Combining transient IR measurements (TRIR), TAS and DFT/TD‐DFPT calculations unveils the reasons for this situation. The TRIR measurements evidence that the photoinduced electrons are located in the inorganic part, while the holes are in the mdip ligand. The longer lifetime of MIP‐177(Ti)‐LT is mapped onto a slower decay of the Ti–O related peaks. A reversible change in the coordination of the carboxylate groups from a bidentate to a monodentate coordination is observed only in MIP‐177(Ti)‐LT. Complementary DFT and TD‐DFPT simulations demonstrate a higher electron delocalization on the inorganic part for MIP‐177(Ti)‐LT (hence, enhanced mobility and slower recombination), thus explaining its superior photocatalytic activity
Speed Vascular Patterns in the Spatial Navigation System
No full textInternational audienceABSTRACT The hippocampal formation is central to spatial navigation, hosting neurons that encode position, direction, and speed. Yet, the brain-wide vascular dynamics supporting these processes remain poorly understood, especially during naturalistic behaviors. Here, we adapted functional ultrasound (fUS) imaging to examine how cerebral blood volume (CBV) changes relate to behavioral parameters in freely moving rats. High-resolution imaging of hippocampal-parahippocampal regions during open-field exploration reveals strong correlations between CBV dynamics and animal speed, with distinct regional activation patterns and temporal delays. Lagged general linear modeling uncovers information flow from the thalamus to parahippocampal regions, including the medial entorhinal cortex, and to hippocampal subfields (dentate gyrus, CA1–CA3), consistent with a hierarchical processing framework. The analysis also links CBV with angular head speed and the dorsal thalamus. Decoding analyses show that CBV signals not only encode speed precisely but also capture spatial features like proximity to walls and corners, even when univariate analyses do not. This decoding remains robust across animals, underscoring the universality of speed encoding in vascular dynamics. We also identify slow CBV oscillations in the hippocampus aligned with minute-scale speed fluctuations, suggesting a neurovascular signature of exploratory behavior. These findings reveal a hemodynamic signature of speed representation in the navigation system, arising from energy demands in a continuous attractor network model for path integration, where population activity and synaptic currents increase quadratically with animal speed as both peak firing rates and neuronal recruitment scale linearly with animal speed. Moreover, they highlight functional ultrasound imaging as a powerful approach for probing the hemodynamic basis of navigation
Adaptive motility enables neutrophils to rapidly navigate confined capillaries
No full textAs the first responders of the immune system, neutrophils rapidly and abundantly reach inflamed tissues through blood capillaries. The diameter of capillaries can be as narrow as two microns, imposing considerable deformations on neutrophils. Notably, capillary obstruction due to neutrophil retention causes vascular dysfunction and contributes to the pathogenesis of several diseases. However, the cellular mechanisms that allow neutrophils to migrate into small capillaries and to avoid retention remain unknown. In this study, we demonstrate, both in vivo and in vitro , that capillary size does not influence neutrophil migration velocity. During migration into capillaries of different sizes, neutrophils maintain high speed, a phenomenon associated with a global actomyosin cytoskeleton rearrangement in response to confinement strength. In irregular capillaries, neutrophils rapidly adapt their cell contractility via the ROCK-MyoII pathway, which allows them to sustain their migration speed along the vessels despite changes in confinement. At the single cell level, inhibition of ROCK impairs actomyosin cytoskeleton rearrangement and reduces neutrophil migration speed within confined capillaries. At the collective level, ROCK inhibition hampers efficient neutrophil trafficking in a network of small capillaries, resulting in vessel obstruction. These findings reveal a unique capacity of neutrophils to rapidly and dynamically adapt their migration to the confinement strength of capillaries, an ability that might limit vascular dysfunction during inflammation
Sustainable Chitosan-Based Composite Materials for the Photodegradation of Wastewater Contaminants
No full textInternational audienceSustainable Chitosan-Based Composite Materials for the Photodegradation of Wastewater Contaminant