HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Resolving the relaxation complexity of vitrimers: Time-temperature superpositions of a time-temperature non-equivalent system
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Upcycling Polyolefin Blends into High-Performance Materials by Exploiting Azidotriazine Chemistry Using Reactive Extrusion
No full textInternational audienceAbstract Cellulose and lignin nanoparticles are high‐value‐added products obtained from lignocellulosic biomasses through several steps of cellulose purification and lignin extraction. These steps drastically reduce the potential feedstock revenue when carried out as stand‐alone methodologies. To increase biomass yields, we describe here a strategy to design a biorefinery focused on producing cellulose and lignin nanoparticles as main products, but also aim to recover and benefit from other biomass components using only water‐based processes. Sequential pressurized liquid extractions and diluted acid and alkaline treatments were carried out to fractionate elephant grass biomass, yielding (for every 100 g of biomass): 30 g of cellulose pulp (converted to 9 g of cellulose nanocrystals and 9 g of cellulose nanofibers); 10 g of lignin (used to produce 8.5 g of stable colloidal lignin nanoparticles by probe‐sonication in water); 7.5 g of extractives (e.g . sterols and phenolics) and 23 g of xylose (converted to 4.1 g of furfural). Alternatively, to allow for the flexible use of the cellulose fraction in the proposed biorefinery, 22 g of glucose could be produced by enzymatic hydrolysis. The results demonstrate that water‐based processes are suitable for a holistic use of biomass, providing a comprehensive set of high‐value‐added co‐products that are renewable and cost‐effective chemical, cosmetic, food, polymer and pharmaceutical solutions
Investigating the Mukaiyama-type epoxidation reaction of alkenes with Cr(III) salophen catalysts: A confrontation between experiments and DFT calculations
No full textInternational audienceThis study aimed at the complete elucidation of the mechanism of the Mukaiyama-type alkene epoxidation reaction using the [(salophen)CrIIICl] precatalyst, by combining spectroscopic (UV–visible and EPR) studies, catalytic reactivity and quantum chemical modeling. These studies performed in parallel allowed us to propose a detailed reaction scheme, in which two consecutive active species incorporating both {salophen(CrV = O)} moieties were formed in situ, resulting in two distinct catalytic regimes
Mécanique de films d'hydrogels : instabilités induites par le gonflement, effets de taille finie, de la rhéologie sans contact à une déshydratation induite par indentation
No full textIn this manuscript, we study the mechanical response of hydrogel thin films from different perspectives, including free-surface instability, fluid-mediated surface indentation and Hertz-like contact situations. A first, preliminary Chapter is deduced to the introduction of basic concepts used is this thesis. Then, in a first part, we focus on swelling-induced surface instabilities that are observed on both swollen hydrogels and dried polymer films. The different observed morphologies are characterized by shape and spacing. We analyse the pattern formation as the result of an important anisotropic swelling of surface-attached films, and a subsequent drying of the already-destabilized free surface of polymer hydrogel. In a second part, we develop a poroelastic model to describe the mechanical response of a permeable hydrogel to any axially-symmetric pressure field, in a general case. Both the infinite-thickness case and finite-size effects are studied and compared. In a third part, we use the latter theoretical framework to address the specific poroelastic lubrication coupling associated with contactless colloidal-probe methods. We derive theoretically the conservative and dissipative components of the force associated with the oscillating vertical motion of a sphere close to the poroelastic substrate. We confront our theoretical results to colloidal-probe Atomic Force Microscopy (AFM) experiments performed on a thick and swollen hydrogel. In a last part, we highlight a succession of several mechanical responses of swollen hydrogels, with Surface Force Apparatus (SFA) experiments. From a regime with no gel-probe interaction, the hydrogel first undergoes a gentle deformation of its surface in a lubricated regime. Then, the indentation of the probe in a contact regime forces the expulsion of the solvent from the polymer matrix. We finally show that, at room temperature, the imposed mechanical load triggers the dehydration-induced glass transition of the polymer. Overall, our results show that the poroelastic response is characterized by a transition in time from a purely elastic and incompressible behaviour to a purely elastic and compressible one.Dans ce manuscrit, nous étudions la réponse mécanique de films minces d'hydrogel sous plusieurs angles, incluant celui d’instabilités de la surface libre, d’indentation de la surface au moyen d’un fluide et de situations proches du contact de Hertz. Un premier chapitre préliminaire est consacré à la présentation des concepts de base utilisés dans cette thèse. Ensuite, dans une première partie, nous nous intéressons à des instabilités de surface induites par gonflement, que l'on observe à la fois sur des hydrogels gonflés et sur des films séchés. Nous analysons la formation de motifs comme le résultat d'un important gonflement anisotrope des films qui sont attachés à une surface, suivi du séchage de la surface libre de l'hydrogel de polymères, d'ores et déjà déstabilisée. Dans une deuxième partie, nous développons un modèle poroélastique pour décrire la réponse mécanique d'un hydrogel perméable soumis à un quelconque champ de pression possédant une symétrie axiale, dans un cas général. Aussi bien le cas d'une épaisseur infinie que les effets de taille finie sont étudiés et comparés. Dans une troisième partie, nous utilisons ce cadre théorique pour aborder le problème spécifique du couplage entre poroélasticité et lubrification, rencontré dans le cadre de techniques en sonde colloïdale et sans contact. Nous aboutissons théoriquement aux composantes dissipative et conservative de la force résultant du mouvement vertical d'une sphère au voisinage du substrat poroélastique. Ces résultats théoriques sont confrontés à des résultats expérimentaux de Microscopie à Force Atomique (AFM) en sonde colloïdale, obtenus sur un hydrogel épais et gonflé. Dans une dernière partie, nous mettons en évidence une succession de réponses mécaniques de la part d'hydrogels gonflés, avec des expériences d'Appareil à Forces de Surface (SFA). Partant d'un régime dénué d'interactions entre la sonde et le gel, la surface de l'hydrogel subit d'abord une faible déformation, dans un régime en lubrification. Enfin, nous montrons qu'à température ambiante la contrainte mécanique imposée déclenche par déshydratation la transition vitreuse du polymère. Dans l’ensemble, les résultats obtenus montrent que la réponse poroélastique est caractérisée par une transition dans le temps allant d’un comportement purement élastique et incompressible à un comportement purement élastique et compressible
Reconstituting the dynamic steady states of actin networks in vitro
No full textInternational audienceDespite the constant renewal of their components, cellular actin networks maintain their overall appearance, through a subtle balance of filament assembly and disassembly. This balance is key to the remodelling of cellular architecture. We discuss the significance of in vitro reconstitutions in deciphering the complexity of actin regulation
Dynamic heterogeneity at the experimental glass transition predicted by transferable machine learning
No full textInternational audienceWe develop a machine learning model, which predicts structural relaxation from amorphous supercooled liquid structures. The trained networks are able to predict dynamic heterogeneity across a broad range of temperatures and time scales with excellent accuracy and transferability. We use the network transferability to predict dynamic heterogeneity down to the experimental glass transition temperature Tg, where structural relaxation cannot be analyzed using molecular dynamics simulations. The results indicate that the strength, the geometry, and the characteristic length scale of the dynamic heterogeneity evolve much more slowly near Tg compared to their evolution at higher temperatures. Our results show that machine learning techniques can provide physical insights on the nature of the glass transition that cannot be gained using conventional simulation techniques
Transforming Cobalt Nanospheres into Co2P Nanorods: The Key Roles of Oleylamine and Organophosphorus Ligands in Co(I) Precursor Uncovered Through XPS Analysis
No full textInternational audienceThis research offers fresh insights into the growth mechanism of cobalt nanoparticles in oleylamine from a precursor with nominal stoichiometry CoCl(PPh3)3, prompting a reevaluation of the model delineated in "The five Shades of Oleylamine" by Moisset et al. (Nanoscale 2021, 13, 11289–11297) that explicated the cobalt sphere-to-rod morphological transition. While the crucial role of oleylamine is reconfirmed, X-ray photoelectron spectroscopy (XPS) discloses the significant involvement of the organophosphorus ligand of the Co(I) precursor. By scrutinizing aliquots from a tetradecane:oleylamine solution, XPS substantiates the disproportionation of Co(I) into Co(II) and Co° during the sphere growth stage in line with the tenets of Five Shades. Pure Co spheres are formed, with phosphorus-containing species disappearing from the XPS probed layers. However, further inspection of washed nanoparticles corroborates the formation of Co-P bonds, with the Co/P atomic ratio nearing 2 for the nanorods. In response to these findings, previously published data and electron diffraction patterns of the nanorods structure are reassessed, conclusively demonstrating that the nanorods are composed of Co2P, contrary to earlier assumptions of pure cobalt content. This leads to a revised depiction of the sphere-to-rod transition, placing emphasis on the role of organophosphorus ligands (triphenylphosphine and, possibly, its oxidation products) that were previously overlooked
Biopathologic Characterization and Grade Assessment of Breast Cancer With 3-D Multiparametric Ultrasound Combining Shear Wave Elastography and Backscatter Tensor Imaging
No full textInternational audienceObjective : Despite recent improvements in medical imaging, the final diagnosis and biopathologic characterization of breast cancers currently still requires biopsies. Ultrasound is commonly used for clinical examination of breast masses. B-Mode and shear wave elastography (SWE) are already widely used to detect suspicious masses and differentiate benign lesions from cancers. But additional ultrasound modalities such as backscatter tensor imaging (BTI) could provide relevant biomarkers related to tissue organization. Here we describe a 3-D multiparametric ultrasound approach applied to breast carcinomas in the aims of (i) validating the ability of BTI to reveal the underlying organization of collagen fibers and (ii) assessing the complementarity of SWE and BTI to reveal biopathologic features of diagnostic interest. Methods : Three-dimensional SWE and BTI were performed ex vivo on 64 human breast carcinoma samples using a linear ultrasound probe moved by a set of motors. Here we describe a 3-D multiparametric representation of the breast masses and quantitative measurements combining B-mode, SWE and BTI. Results : Our results reveal for the first time that BTI can capture the orientation of the collagen fibers around tumors. BTI was found to be a relevant marker for assessing cancer stages, revealing a more tangent tissue orientation for in situ carcinomas than for invasive cancers. In invasive cases, the combination of BTI and SWE parameters allowed for classification of invasive tumors with respect to their grade with an accuracy of 95.7%. Conclusion : Our results highlight the potential of 3-D multiparametric ultrasound imaging for biopathologic characterization of breast tumors