WorldCat Identities

Pignon, Frédéric (19..-....; géophysicien)

Overview
Works: 26 works in 29 publications in 2 languages and 52 library holdings
Roles: Thesis advisor, Contributor, Other, Opponent, htt, Author
Classifications: QC189.5, 531.1134
Publication Timeline
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Most widely held works by Frédéric Pignon
La mesure en rhéologie : Des avancées récentes aux perspectives by Alain Ponton( )

1 edition published in 2021 in French and held by 9 WorldCat member libraries worldwide

La rhéologie est une spécialité située à l'interface de plusieurs disciplines : la physique, la mécanique des fluides, la mécanique des solides et la physico-chimie de la matière molle. Elle constitue un outil analytique très puissant mais la mise en œuvre et l'analyse des tests expérimentaux qu'elle réalise, soulèvent des problèmes tant théoriques que techniques. Écrit par les meilleurs spécialistes français de la rhéométrie, ce livre couvre la très large diversité des comportements rhéologiques connus, ainsi que la grande variété des outils expérimentaux et théoriques élaborés pour caractériser ces comportements. Il offre un panorama des méthodes utilisées et de la mise en œuvre de la mesure rhéologique, par un éclairage de certaines analyses classiques, mais surtout par une approche des techniques récentes et novatrices. La présentation est concrète et pédagogique en illustrant les différentes analyses par de nombreux exemples empruntés tant au domaine académique qu'industriel. Cet ouvrage de référence s'adresse aux enseignants, aux étudiants (master, doctorat, élèves ingénieurs), aux chercheurs, mais aussi, de par sa recherche de simplicité et de pédagogie, à tout lecteur pratiquant ou susceptible de pratiquer les analyses expérimentales de la rhéologie
La mesure en rhéologie des avancées récentes aux perspectives by Groupe français de rhéologie( )

1 edition published in 2021 in French and held by 6 WorldCat member libraries worldwide

La rhéologie est une spécialité située à l'interface de plusieurs disciplines : la physique, la mécanique des fluides, la mécanique des solides et la physico-chimie de la matière molle. Elle constitue un outil analytique très puissant mais la mise en œuvre et l'analyse des tests expérimentaux qu'elle réalise, soulèvent des problèmes tant théoriques que techniques. Écrit par les meilleurs spécialistes français de la rhéométrie, ce livre couvre la très large diversité des comportements rhéologiques connus, ainsi que la grande variété des outils expérimentaux et théoriques élaborés pour caractériser ces comportements. Il offre un panorama des méthodes utilisées et de la mise en œuvre de la mesure rhéologique, par un éclairage de certaines analyses classiques, mais surtout par une approche des techniques récentes et novatrices. La présentation est concrète et pédagogique en illustrant les différentes analyses par de nombreux exemples empruntés tant au domaine académique qu'industriel. Cet ouvrage de référence s'adresse aux enseignants, aux étudiants (master, doctorat, élèves ingénieurs), aux chercheurs, mais aussi, de par sa recherche de simplicité et de pédagogie, à tout lecteur pratiquant ou susceptible de pratiquer les analyses expérimentales de la rhéologie
Rhéologie micronique : adhésion de levures saccharomyces cerevisiae sur le verre by Mickaël Castelain( Book )

2 editions published in 2007 in French and held by 2 WorldCat member libraries worldwide

Microorganisms are ubiquitous in both industrial and natural environment and their adhesion to surfaces are unavoidable. At the local cell scale and at the first time of contact, study of adhesion aims at understanding how and why these biological objects tether to surfaces. We have been interested in mechanisms involved in Saccharomyces cerevisiae yeast adhesion to glass substrates with an optical tweezer. This work has been carried out as to quantify interaction forces regarding environmental parameters such as ionic strength, contact time, cation valency (mono-jdivalent) and measurement temperature. Adhesion mechanisms at the initial contact and removal forces have been carried out and highlight that environmental parameters influence S. cerevisiae adhesion to glass
Rhéologie des dispersions aqueuses thixotropes d'une argile de type hectorite by Frédéric Pignon( Book )

2 editions published in 1997 in French and held by 2 WorldCat member libraries worldwide

LE BUT DE CETTE ETUDE EST L'IDENTIFICATION ET LA COMPREHENSION DES MECANISMES GOUVERNANT LE COMPORTEMENT THIXOTROPE DANS LES DISPERSIONS AQUEUSES D'UNE ARGILE DE TYPE HECTORITE : LA LAPONITE. CETTE ARGILE MODELE, CONSTITUEE DE PARTICULES ANISOTROPES DE TAILLE NANOMETRIQUE, A PERMIS DE COMBINER LES MESURES RHEOMETRIQUES AVEC DES MESURES DE DIFFUSION DE RAYONNEMENTS, DES VISUALISATIONS DU CHAMP DE DEFORMATION ET DES MESURES DE BIREFRINGENCE. AU REPOS, LA STRUCTURE DES GELS EST CONSTITUEE D'AGREGATS MICRONIQUES DENSES ASSEMBLES EN UNE MASSE FRACTALE D'UNE DIMENSION D. PRES DE LA TRANSITION SOL-GEL, D = 1, LA TEXTURE EST FIBREUSE. AUX FRACTIONS VOLUMIQUES PLUS ELEVEES, D = 1,8, LA STRUCTURE EST UNE CONNEXION DE ZONES DENSES ET DE ZONES MOINS DENSES EN PARTICULES. DES LOIS D'ECHELLES THEORIQUES ET EXPERIMENTALES, ONT PERMIS DE CORRELER CES DIMENSIONS FRACTALES A L'INFLUENCE DE LA FRACTION VOLUMIQUE SUR LE SEUIL D'ECOULEMENT. LA TRANSITION SOL-GEL ET LA STABILITE DE LA PHASE GEL ONT ETE ETUDIEES EN FONCTION DU TEMPS DE GELIFICATION ET DES PARAMETRES PHYSICO-CHIMIQUES. L'EXISTENCE D'INSTABILITES D'ECOULEMENTS, TELLE QUE LA LOCALISATION DU CISAILLEMENT, ONT ETE MONTREES, SUR CES DISPERSIONS DONT LA COURBE D'ECOULEMENT EST A MINIMUM DE CONTRAINTE. LES DIFFERENTS REGIMES D'ECOULEMENTS ONT ETE IDENTIFIES ET ONT PERMIS D'ETABLIR DES PROCEDURES FIABLES POUR LA CARACTERISATION DU COMPORTEMENT THIXOTROPE. SOUS ECOULEMENT DE CISAILLEMENT, LA CHUTE DE VISCOSITE PROVIENT D'ORIENTATIONS ET DE DESAGREGATION A L'ECHELLE DE LONGUEUR DE L'ORDRE DU MICRON. LORS DE LA RESTRUCTURATION, LES DEUX ECHELLES DE TEMPS MISES EN EVIDENCE, CORRESPONDENT RESPECTIVEMENT A UNE RELAXATION RAPIDE DES ORIENTATIONS ET A UN PROCESSUS LENT D'AGREGATION. LA NATURE DU COMPORTEMENT THIXOTROPE EST ALORS IDENTIFIEE COMME ETANT PRINCIPALEMENT UN PROCESSUS D'AGREGATION REVERSIBLE, POUR LEQUEL LES GRANDES ECHELLES DE LONGUEUR, DE L'ORDRE DU MICRON, ASSOCIEES A UN ARRANGEMENT FRACTAL JOUENT UN ROLE DETERMINANT
Etude expérimentale de la formation des biofilms sous conditions hydrodynamiques contrôlées by Ana Cecilia de Andrade Pinho Medeiros( )

1 edition published in 2016 in French and held by 2 WorldCat member libraries worldwide

In the aquatic environment, 90% of microorganisms are present as a biofilm rather than free-swimming cells. Biofilms may develop on most of humid surfaces, in particular, in porous media for their high specific surface area. Biofilm formation in porous media is very interesting subject for many scientific researchers, because of its relevance to many industrial processes such as water treatment, soil bio- mediation, oil recovery and CO2 storage. However, the development of the biofilm is not just a passive aggregation of bacteria cells. It involves biological, physical and chemical interactions with the bacteria's micro-environment. Several studies in macroscopic scale have shown that hydrodynamic conditions in porous media play an essential role on the dynamics of biofilm growth, which in turn affects hydrodynamic properties of porous media such as porosity, permeability and pressure drop. In this thesis we have developed an experimental device and an appropriate methodology for the characterization of biofilm's structure. An experimental study on the influence of fluid flow on the formation and structure of biofilms was performed using a bacterial strain Pseudomonas putida. Biofilms were grown in micro Hele-Shaw flow cell (in PDMS or PMMA) under laminar flows (Re=0.04~2) and fed continuously with a nutrient medium. Characterization of initial colonization was also carried out in order to examine the statistical variability and reproducibility of experiments. Biofilm formation on a solid support under a sheared flow (Re=0.04 (0.0021 Pa) and Re = 2 (0.094 Pa)) was evaluated after 24, 48 and 72h of development. Observations were made under a confocal laser scanning microscopes using fluorescent tag. 2D images were taken at different positions in the flow cell and used to perform a 3D reconstruction of biofilm's structure and an evaluation of its spatial distribution for an observation area of 12 *12mm². The results show that biofilms formation is not sensitive to initial colonization. A stratification of biofilm was also observed. The inner layer has a thin thickness (5~10 µm), but with a dense structure, while the outer layer show rather a filamentous structure. The ratio of volume fractions between these two layers varies from 3 to 12, depending on the formation time. This difference is more important in the case of low shear stress than that of high shear stress, which means that the upper part of the biofilm seems to be controlled by the hydrodynamic conditions. By analyzing the spatial distribution of the biomass, we found that after 48h, the biofilm present a significant heterogeneity and the volume fraction of biomass decreases after 72h for both two hydrodynamic conditions, which suggests probable detachments or erosions of biofilm. Concerning the growth kinetics, different apparent growth rates were observed for each observation time. These values are significantly below the growth rates observed in free culture medium. This result also indicates a possible effect of hydrodynamics on the growth of biofilm. This experimental study of biofilm formation in micro-scale allowed us to obtain the information on the biofilm structural and its apparent growth rate, as well as the hydrodynamic effect on its properties across several pores of the porous media. This scaling up makes it's possible to develop eventually mathematical models to simulate the evolution biofilm's morphology and its spatial distribution in the porous medium
Interactions effectives et dynamiques en systèmes actifs de colloïdes autopropulsés by Enrico Federico Semeraro( )

1 edition published in 2017 in French and held by 2 WorldCat member libraries worldwide

This project aimed to systematically investigate the interactions, microstructure and dynamics in suspensions of colloidal particles that mimic active motions, using (Ultra) Small- Angle X-ray Scattering (USAXS/SAXS) and X-ray Photon Correlation Spectroscopy (XPCS). As opposed to the conventional passive colloids (Brownian particles), active colloids are non-equilibrium systems consisting of self-propelled particles that display many fascinating dynamics, such as streaming, swarming, flocking, etc. in appropriate media. Practical examples of active systems are motile microorganisms, such as some species of bacteria, or synthetic Janus colloids - characterized by an asymmetric chemical composition of their surface - that can induce a propulsion mechanisms, like self-diffusiophoresis. The foci of this thesis are on interparticle interactions, particle-medium interactions and the phoretic dynamics in active systems.Firstly, the structure and motility of Escherichia coli bacteria were investigated by combined USAXS and SAXS methods. As an offshoot, the scattering data spanning a broad scattering vector (q)-range permitted the derivation of a multiscale structural model by combining colloidal (cell-body), membrane (cell-envelope) and polymer (flagella) features. This model was further refined by contrast-variation Small Angle Neutron Scattering (SANS) measurements on E. coli suspensions at three match points and the full contrast which allowed the determination of the membrane electron-density and the inter-membrane distances on a quantitative scale.These bacteria were then used as active component in a mixture with micron-sized passive silica colloids, with the aim of investigating how the effective interactions and dynamics of passive colloids are affected by the presence and the motility of active E. coli. Both static and hydrodynamic information were obtained via the simultaneous use of USAXS and XPCS techniques. Data suggested active bacteria act as a fluidizing agent in such systems, reducing attractive interactions and enhancing the dynamics of passive colloids, which, at the same time, are affected by the buffer and more viscous environment due to the bacterial presence.Finally, the phoretic motions of micron-sized silica colloids and half-coated silica/nickel Janus colloids suspended in a mixture of 3-methylpyridine (3MP) and water/heavy water undergoing liquid-liquid phase separation were investigated using USAXS and XPCS. Due to the preferential wetting of 3MP on the silica surface, the motion of the colloids is strongly correlated to the dynamics of phase separation.Silica colloids displayed advective motion with enhanced diffusion toward the 3MP-rich phase reminiscent of self-propelled motion until the phase separation is completed. Suspensions of Janus colloids showed a much richer scenario, where colloid dynamics are strongly influenced by the asymmetric interactions with the solvent. The dynamics of Janus colloids were either enhanced or suppressed depending on the 3MP concentration, which, concurrently, affected the microstructure of the system. As opposed to the partitioning in 3MP-rich phase in the case of silica colloids, Janus particles behave like surfactants at the interface.The thesis demonstrates the ability of studying active systems by means of scattering methods and probe their behaviour in the thermodynamic limit and complement the information derived from direct microscopy observations
Compréhension et maîtrise des mécanismes de structuration des dépôts lors de la filtration tangentielle de produits laitiers by Christopher David( Book )

2 editions published in 2008 in French and held by 2 WorldCat member libraries worldwide

Membrane separation processes are commonly used in dairy industry to concentrate and purify nano-particles dispersions. The main limitation of these separation processes is the accumulation of colloids on the membrane. The comprehension of the colloidal interactions and aggregations taking place in these deposits constitute a major technological challenge. The dispersions studied are casein micelles suspensions prepared in different aqueous phase. The effects of the physicochemical properties and the rheological behavior of the dispersion on the organization of the nano-particles and flow behavior were investigated and three domains of concentration were identified. New frontal and cross-flow filtration cells have been developed and combined with in-situ small angle x-ray scattering. The filtration properties have thus been linked to the spatial and temporal evolution of the casein micelles' concentration and structure at the pertinent nanometric length scales in the accumulated layers
Conditions hydrodynamiques et organisation structurale dans le dépôt formé lors de l'ultrafiltration tangentielle : application à la bioraffinerie by Candice Rey( )

1 edition published in 2017 in French and held by 2 WorldCat member libraries worldwide

Membrane separation processes commonly used in several industrial applications, like bio and agro industries, waste water and clean water treatments, are more and more exploited in biorefinery. As an example, cross-flow ultrafiltration process shows a high potential in separation protocol of raw feed components like cellulose nanocrystals to produce biomass. This process is limited by the increase of particles concentration at the membrane surface, which conducts to phenomena named concentration polarization and fouling, which decrease the filtration performance. The PhD work objective is to bring a better understanding of the mechanisms involved in the formation of these phenomena. Two characterization methods covering length scales from nanometer to micrometer have been developed thanks to new designed tangential ultrafiltration cells allowing to link the ultrafiltration process to small angle X rays scattering and to micro particle image velocimetry. These measurement performed in-situ during ultrafiltration of nanocrystal celluloses and Laponite clay suspensions have allowed characterizing the structural organization and the velocity field within the concentration polarization layers. The correlation of these results with the rheological behavior properties of the suspensions, have permitted to access for the first time to the stress field within the concentration polarization and fouling layer during the tangential ultrafiltration process
Nanofibres de cellulose pour la production de bionanocomposites by Oleksandr Nechyporchuk( )

1 edition published in 2015 in English and held by 2 WorldCat member libraries worldwide

Un des principaux challenges dans le contexte du développement des matériaux biocomposites est de remplacer les matières plastiques à base de pétrole par des matériaux biosourcés. En raison de leurs origines naturelles, d'une résistance relativement élevée et de leur capacité à former des produits transparents, les nanofibres de cellulose possèdent un grand potentiel d'applications dans les matériaux composites. Dans ce travail des résultats ont été apportés premièrement sur l'optimisation des procédés de productions de nanofibres de cellulose par des traitements biochimiques et mécaniques, deuxièmement sur leurs propriétés rhéologiques et structurelles en milieu aqueux et troisièmement sur la production de composites à matrice de latex. Les questions de dispersions homogènes de nanofibres de cellulose dans la matrice et des interactions entre ces composants à des fins de renforcement des bio-composites ont été étudiés en détails
Écoulements de fluides à seuil autour d'un cylindre en milieu confiné : études expérimentale et numérique by Hamdullah Ozogul( )

1 edition published in 2016 in French and held by 2 WorldCat member libraries worldwide

The flow of yield stress fluids around a circular cylinder in a confined geometry has been investigated with a Poiseuille flow configuration.Experimentally, a test set-up was built which provides a continuous flow in a closed loop. We studied creeping, recirculating and vortex shedding flow regimes. New results has been realised with a Newtonian fluid and Carbopol solutions, models for yield stress behaviour in laboratory experiments and in industry. A high speed camera and a laser sheet have been used to perform images which are treated by PIV. Kinematic fields, flow morphologies and critical transition parameters have been determined.Numerically, a viscoplastic model based on the regularised Herschel-Bulkley law has been used. Results as flow morphologies, rigid areas and local flow parameters fields have been performed. That allowed us to compare the intrinsic effects of Carbopol solutions and the viscoplastic numerical model. A specific study on the wall slip has also been considered with an elasto-hydrodynamic lubrication model
Concentration effect of TEMPO-oxidized nanofibrillated cellulose aqueous suspensions on the flow instabilities and small-angle X-ray scattering structural characterization by Oleksandr Nechyporchuk( )

1 edition published in 2015 in English and held by 2 WorldCat member libraries worldwide

Couplage hydrodynamique-biomasse dans les procédés de dépollution. Approche locale des mécanismes de croissance et d'adhésion/détachement de micro-organismes sur substrats solides by Serigne Mbaye( )

1 edition published in 2011 in French and held by 2 WorldCat member libraries worldwide

The biofilms, mainly composed of micro-organisms and exopolymers, develop themself on nonsterile wet surfaces. They are of considerable importance in many industrial and environmental applications, among which biofilters used in water treatment. The strong interaction between the flow and the biofilm development in this type of processes returns very difficult their modelling without drastic progress in the comprehension of phenomena appearing on various scales (biofilm, pore, biofilter). This thesis aims to bring a better comprehension of the mechanisms which control the biofilm growth on a local scale. A flow chamber characterized by a laminar flow profile was developed to allow the in-situ observation and the analysis of cell adhesion, detachment and the growth of P. putida bacteria under sheared flow. The results also showed that the growth kinetics measured in batch was not applied, for low Reynolds number in the case of a biomass fixed to solid support and subjected to a shear stress. The study revealed also, as already shown before in certain research tasks, the biofilms organization in response to the sheared flow. The technique of 3d-reconstruction developed and implemented in complement to the direct optical microscopy allowed a better interpretation of global biofilm architecture and have explained how the microstructure can influence the biofilm friction toward fluid flow. We have simulated the distribution of the local velocity profiles in biofilm microstructure and our estimation of permeability has highlighed the importance of local distribution of biomass in this parameter
Rhéologie de suspensions hétérogènes concentrées : applications aux bols alimentaires et aux jus gastriques d'aliments solides. by Jeremy Patarin( )

1 edition published in 2014 in French and held by 2 WorldCat member libraries worldwide

The challenge of this work is to carry out the rheological characterization of concentrated suspensions of viscoplastic objects suspended in a viscoelastic matrix. Three structural constraints are faced: the heterogeneity of the particles, the size of particle in relation to the size of the whole system studied, and the proximity between the consistency of the suspending phase and that the consistency of the particles. In the food context, some biological constraints are added: small lifetimes of bolus, in vivo sampling and test conditions of temperature and humidity. All these constraints lead to a compromise in rheometry, at the edge of continuum mechanics, aiming to measure useful rheological properties. To carry out the rheological characterizations quickly and efficiently, two original devices has been designed trough this work. Applied to food bolus from cheese, rheology comes to govern flows in the mouth and induce the creation of exchange area in the mouth, during the chewing process. Through these interfaces, the savors and flavors are released and transported to the sensory receptors. The results show the relationship between the yield stress of the bolus and flavors release of different hydrophobic aromas, depending on the firmness and fat content of the cheeses. Specifically, fluid suspending matrix appears to play a major role in the creation and persistence of exchange area.Applied to gastric juice from bread, the issue is whether changes in carbohydrate content could impact the rheology of gastric juice, modify the kinetics of stomach flow rate, and decrease the glycemic excursion. The results show the effect of amylose addition on increasing the viscosity for long digestion time, when the rheology is no longer governed by the jamming effect of the particles made of water-swollen bread. However, amylose does not seem to have any impact on the kinetics of emptying, which reinforces that the stomach flow rate is regulated by the caloric charge contained in the meal
Procédés de séparation membranaire de colloïdes : caractérisation des mécanismes aux échelles nanométriques et intensification par ultrasons by Yao Jin( )

1 edition published in 2014 in English and held by 2 WorldCat member libraries worldwide

This thesis studies an ultrasonic assisted cross-flow ultrafiltration process from macro tonano scales. Different types of colloids were investigated: synthetic and natural clay dispersions,casein micelles (skim milk) and starch or cellulose nanocrystal suspensions. Firstly, flowproperties and the changes due to ultrasound (US) were investigated. Secondly, structuralorganizations at nanometer length scales in the vicinity of the membrane during filtration havebeen revealed for the first time by real-time in-situ Small Angle X-ray Scattering. The applied USincreased significantly the permeate flux of ultrafiltration by an enhancement factor of 1.6 to13.5, depending on the structural organization of the colloids. The applied US has led to threemain effects: a removal of accumulated particle layer, a partial disruption or no change of thenano-organization. Thirdly, thanks to the obtained concentration profiles, a modeling approachhas allowed a prediction of the permeate flux
Impact of sonication on the rheological and colloidal properties of highly concentrated cellulose nanocrystal suspensions by Erwan Gicquel( )

1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide

Study of concentrated boehmite suspensions containing anisotropic colloidal particles : phase diagram, structure and rheology - Application to membrane separation processes by Maria Dronova( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

L'amélioration des procédés industriels tels que la filtration de suspensions de colloïdes nécessite une compréhension approfondie de la stabilité colloïdale qui est pilotée par les interactions interparticulaires. Afin de comprendre les mécanismes à l'œuvre à la fois dans la cinétique de croissance des dépôts de filtration et dans leur structuration, une double stratégie a été adoptée pour étudier les suspensions de boehmite. Tout d'abord, nous avons réalisé des expériences de filtration frontale et avons mis en évidence une variation non triviale de la perméabilité des gâteaux de filtration en fonction de la force ionique des suspensions de boehmite. En étudiant des suspensions de boehmite concentrées par stress osmotique en combinant des mesures par diffusion centrale des rayons X aux petits angles et de rhéologie, il apparait que la plus faible perméabilité des gâteaux de filtration obtenus à partir de suspensions de force ionique intermédiaire (pour laquelle la double couche de Debye est du même ordre de grandeur avec la longueur des particules) résulterait d'un ordre orientationnel local. Enfin, des expériences de filtration couplées avec des observations en temps réel par microtomographie X ont permis d'enregistrer les profils de concentration en boehemite dans les gâteaux de filtration. Ces expériences ont mis en évidence l'influence de la force ionique sur la forme des profils de concentration. L'ensemble de ces résultats montrent les effets combinés des forces interparticulaires, de l'anisotropie et de la dimension des particules sur la structuration des gâteaux de filtration et leurs propriétés de transport
Compression osmotique microfluidique : caractérisation rapide de dispersions colloïdales et de formulations industrielles by Camille Keïta( )

1 edition published in 2021 in French and held by 1 WorldCat member library worldwide

Caractériser les dispersions colloïdales en fonction de leur concentration en colloïdes en un minimum de temps constitue le cœur du sujet de cette thèse. Pour y parvenir, des mesures de la pression osmotique des dispersions, c'est-à-dire de leur résistance à la compression, peuvent être réalisées à différentes concentrations et pour diverses conditions expérimentales (salinité, pH etc.). L'utilisation classique de sacs de dialyse permet de telles mesures, mais, inconvénients majeurs, ces expériences dites « de compression osmotique » nécessitent des semaines d'équilibrage et ne peuvent pas être suivies in-situ. Le but de ces travaux consiste donc à mettre en œuvre des expériences de compression osmotique à haut débit, permettant également d'observer in-situ le système colloïdal à l'étude.Pour se faire, l'échelle microfluidique (10-100 µm) apparaît comme pertinente. A la suite du prototypage ultra-rapide de dispositifs fabriqués en PEG-diacrylate, l'enjeu est d'y intégrer des membranes nanoporeuses par photopolymérisation in-situ d'un hydrogel de PEGDA. La puce microfluidique ainsi transformée en un « micro-osmomètre à membrane », mesures de la pression osmotique des dispersions et observations in-situ à tout instant de l'expérience et en tout point du système sont alors possibles, à l'aide d'un simple microscope optique.Grâce à cette technologie, l'équation d'état d'une dispersion colloïdale, c'est-à-dire l'évolution de sa pression osmotique en fonction de sa concentration, mais également nombre d'informations sur l'état physico-chimique des particules ou encore sur leur organisation structurale pendant la compression peuvent être obtenues, en seulement quelques heures, ouvrant ainsi la voie à un criblage rapide de divers fluides complexes
Filtration de dispersions de micelles de caséine. : Propriétés physiques, rhéologiques et cohésives des couches concentrées accumulées à la surface de la membrane. by Floriane Doudies( )

1 edition published in 2019 in French and held by 1 WorldCat member library worldwide

Lors de l'ultra- ou de la microfiltration de lait écrémé, les micelles de caséine, particules colloïdales poreuses et déformables, viennent s'accumuler à la surface des membranes passant de l'état liquide (sol) à l'état solide (gel) sous certaines conditions. Cela conduit à des altérations notables des performances de la filtration. Afin de mieux maîtriser les opérations de filtration, il est nécessaire de mieux connaître les conditions opératoires qui conduisent à la formation de ces gels et leurs propriétés. Deux stratégies ont été adoptées pour cela : (i) une approche ex-situ, pour étudier les propriétés physiques, rhéologiques et cohésives des micelles de caséine concentrées; (ii) une approche in-situ par diffusion de rayons X aux petits angles (SAXS) lors de l'ultrafiltration de micelles, afin de suivre les évolutions spatio-temporelles des profils de concentration en micelles de caséines à la surface de la membrane.Par l'approche ex-situ, il a été mis en évidence des différences de comportement entre les dispersions de micelles de caséine à 7 et 20°C : à 7°C les micelles de caséine sont moins compressibles, leur concentration de transition sol-gel est plus basse et elles développent des interactions plus cohésives qu'à 20 °C. Par l'approche in-situ, les résultats montrent qu'il est possible d'éliminer partiellement les dépôts formés durant les filtrations tangentielles et frontales, en relâchant la pression appliquée. L'élimination du dépôt semble se faire par gonflement du gel de micelles de caséine par diffusion du solvant à la fois du côté de la veine liquide (cô
Stabilization and structural study of new nanocomposite materials by Jessica Link( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The general context of this PhD thesis is the development of highly filled polymer- silica model nanocomposites by solvent route, based on copolymers of vinylidene fluoride and hexafluoropropylene, denoted as P(VDF-co-HFP). Due to their unique combination of mechanical, dielectric, piezoelectric and pyroelectric properties, PVDF and VDF-copolymers combined with silica are good candidates for new advanced applications like actuation or energy harvesting. In this context, the primary objective was to understand how the filler surface chemistry and formulation parameters, as well as the solvent casting process, affect the final structure and properties of the materials. To elaborate P(VDF-co-HFP) nanocomposites with silica by solvent casting, a first step was to prepare solutions of silica and the polymer in a common solvent which will be subsequently dried. Aliphatic ketone solvents of various chain length, namely methyl ethyl ketone (MEK) and 2-heptanone, were used. For this purpose a generic approach to transfer silica nanoparticles from water to organic solvent through a transfer agent was developed. VDF-based copolymer solutions (filled or not with nanoparticles) exhibit thermoreversible gelation in ketone solvents, which may subsequently impact the processing of materials by solvent casting. Studying the phenomenology of PVDF gelation in thus of major concern for controlling the processing of those nanocomposites. No general consensus on the gelation mechanisms is found in the literature. In this context, the gelation of a semi-crystalline P(VDF-co-HFP) in MEK or 2-heptanone was studied. The gelation kinetics was investigated by tube-tilting and linear rheology. A combination of 19F Nuclear Magnetic Resonance (NMR), DSC, SAXS, WAXS and nonlinear rheology was used to probe the structure of these systems and the gelation mechanisms. 19F NMR shows the occurrence of a polymer network-like structure with rigid zones which may act as cross-links. Such a behavior is only observed in the gel state: no polymer network or rigid zones are present when the polymer solution is in the liquid state. The nature and volume fraction of the rigid zones present in the gel state were investigated with DSC and X-ray diffraction. A small crystalline fraction, which may correspond to the rigid zones, is observed in gels. In a third step, the impact of adding silica nanoparticles on the gelation kinetics of P(VDF-co-HFP) was studied. To do so, copolymer - silica gels were formulated in MEK and 2-heptanone using two sources of organic silica solutions, the one prepared previously by phase transfer and a commercial one from Nissan. We found that the presence of silica nanoparticles hardly disturbs the gelation of P(VDF-co-HFP). Conversely, the process, and more particularly the presence of residual water within the material, has a strong impact on the structure of the gels and gelation kinetics.The nonlinear rheological properties of the P(VDF-co-HFP) physical gels filled or not with silica nanoparticles were investigated in 2-heptanone only (as MEK is too volatile), using Large Amplitude Oscillatory Shear (LAOS) experiments (Chapter 5). The behavior of all materials changes from elastic at small strain to viscous at high strain amplitudes. Before abruptly changing from elastic to viscous behavior, unfilled gels exhibit strong strain-hardening. Incorporating silica nanoparticles is found to inhibit strain-hardening. In a last step, P(VDF-co-HFP) - silica solid films were obtained by solvent casting the previously prepared systems. Homogeneous materials filled up to 40 wt% of silica nanoparticles were obtained, with different and finely controlled dispersion states of nanoparticles, related to the structure of the initial gels or solutions. The impact of the concentration and dispersion state of the fillers on the mechanical performances (particularly the mechanical toughness) was investigated
Mécanisme de filtration des suspensions de microgel by Swati Kaushik( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The flow of suspensions in porous media is a complex phenomenon due to the mechanisms involved such as both shear and extensional flows (Herzig, Leclerc, & Goff, 1970). Their use in industrial applications is quite extensive with one of the major applications being at various stages of oil and gas production operations. At several stages of a well construction, flow of fluid between the well and the surrounding porous rock formation is prevented thanks to the polymeric fluid loss control additives. Fluid loss is a severe problem if not controlled, which would add up to the total cost of operations and more importantly could have hazardous impacts on the environment or operators. Among several technologies industrially available, polymeric additives popularly known as fluid loss additives such as microgels and latex particles are added to the injected fluids to limit the loss of fluid (usually water) via the mechanism of pore clogging/jamming in porous media.Many of these fluid loss additives have been tested for their jamming behaviour by conventional methods which involve the application of a high pressure difference (typically 35-70 bars) on the formulated fluid comprising of the additives against a filter representative of the formation's typical pore size (either a metallic grid, ceramic or filter paper) and the measurement of the filtrate volume versus time. However, these standard methods do not give any insight in understanding the underlying mechanism of jamming dynamics in porous media, hence, a better understanding of the mechanism of jamming in porous media by industrial fluid loss additives is needed.In this work, we use chemically cross-linked microgel suspensions as the fluid loss additive and study its jamming behaviour in transparent model porous media. We make use of polydimethylsiloxane (PDMS) devices as model porous media which allows direct observation of the jamming process coupled with quantitative measurements. We fabricate microfluidic devices for frontal flow filtration and lateral flow filtration with different pore sizes to see how parameters like surface wettability, particle concentration, particle size and flow rates affect the filter cake formation.We present a method of controlling the size of the microgel suspensions. We then describe an approach for preparing higher concentration suspensions and investigate the rheology of the suspensions as a function of concentration. Furthermore, we present a simple method of forming a filter cake of the microgel suspension on a supporting membrane and estimate the permeability of the filter cake formed for the flow of water using Darcy's law
 
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Pignon F wetenschapper

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English (7)