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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Etude expérimentale de l'instabilité de digitation visqueuse de fluides rhéofluidifiants modèles / Experimental study of viscous fingering instability of shear thinning fluid models

Chinaud, Maxime 17 December 2010 (has links)
Ce travail de thèse est consacré à l'étude des instabilités de Saffman-Taylor de fluides complexes modèles. Ces derniers sont des solutions de Xanthane dont le caractère rhéofluidifiant augmente avec la concentration en polymère. Dans un premier temps, nous avons étudié les propriétés rhéologiques de ces fluides modèles puis nous avons caractérisé leurs propriétés d'écoulement dans une cellule de Hele-Shaw de forte épaisseur. Dans un deuxième temps, nous avons mesuré par PIV (Particles Image Velocimetry) la distribution du champ de vitesse autour des doigts de Saffman-Taylor pour l'ensemble des fluides étudiés. Afin de valider les expériences de PIV, nous avons caractérisé les vitesses de sédimentation des traceurs, par la technique complémentaire de vélocimétrie par Speckle ultrasonore (Ultrasonic Speckle Velocimetry). Nous avons montré expérimentalement que le champ de vitesse pour tous les fluides est irrotationnel et que la forme du doigt peut être modélisé par un écoulement potentiel autour d'un solide de Rankine. Les expériences ont établi que le rayon de courbure à l'extrémité des doigts est l'unique paramètre qui dépend des propriétés rhéologiques des solutions de Xanthane. De plus, ce paramètre conditionne toute l'hydrodynamique autour des doigts de Saffman-Taylor. / This thesis is devoted to the study of Saffman-Taylor instabilities of complex fluids models. These are solutions of xanthan whose shear thinning behavior increases with polymer concentration.Initially, we studied the rheological properties of model fluids and then we characterized the properties of flow in a Hele-Shaw thick. In a second step, we measured by PIV (Particle Image Velocimetry) distribution of the velocity field around the fingers of Saffman-Taylor for all fluids studied. To validate the PIV experiments, we characterized the sedimentation rates of tracers, by the complementary technique of ultrasonic speckle velocimetry (Ultrasonic Speckle Velocimetry).We have shown experimentally that the velocity field for all fluids is irrotational and that the shape of the finger can be modeled by a potential flow around a Rankine solid. Experiments have shown that the radius of curvature at the top of the fingers is the only parameter which depends on the rheological properties of xanthan solutions.In addition, this parameter influences the whole hydrodynamic around Saffman-Taylor fingers.
2

SHEAR RHEOMETRY PROTOCOLS TO ADVANCE THE DEVELOPMENT OF MICROSTRUCTURED FLUIDS

Eduard Andres Caicedo Casso (6620462) 15 May 2019 (has links)
<p></p><p>This doctoral dissertation takes the reader through a journey where applied shear rheology and flow-velocimetry are used to understand the mesoscopic factors that control the flow behavior of three microstructured fluids. Three individual protocols that measure relative physical and mechanical properties of the flow are developed. Each protocol aims to advance the particular transformation of novel soft materials into a commercial product converging in the demonstration of the real the chemical, physical and thermodynamical factors that could potentially drive their successful transformation. </p> <p> </p> <p>First, this dissertation introduces the use of rotational and oscillatory shear rheometry to quantify the solvent evaporation effect on the flow behavior of polymer solutions used to fabricate isoporous asymmetric membranes. Three different A-B-C triblock copolymer were evaluated: polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(4-vinylpyridine) (ISV); polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>N</i>,<i>N</i>-dimethylacrylamide) (ISD); and polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>tert</i>-butyl methacrylate) (ISB). The resulting evaporation-induced microstructure showed a solution viscosity and film viscoelasticity strongly dependent on the chemical structure of the triblock copolymer molecules. </p> <p> </p> <p>Furthermore, basic shear rheometry, flow birefringence, and advanced flow-velocimetry are used to deconvolute the flow-microstructure relationships of concentrated surfactant solutions. Sodium laureth sulfate in water (SLE<sub>1</sub>S) was used to replicate spherical, worm-like, and hexagonally packed micelles and lamellar structures. Interesting findings demonstrated that regular features of flow curves, such as power-law shear thinning behavior, resulted from a wide variety of experimental artifacts that appeared when measuring microstructured fluids with shear rheometry.</p> <p> </p> <p>Finally, the successful integration of shear rheometry to calculate essential parameters to be used in a cost-effective visualization technique (still in development) used to calculate the dissolution time of polymers is addressed. The use of oscillatory rheometry successfully quantify the viscoelastic response of polyvinyl alcohol (PVA) solutions and identify formulations changes such as additive addition. The flow behavior of PVA solutions was correlated to dissolution behavior proving that the developed protocol has a high potential as a first screening tool.</p><br><p></p>

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