Propriétés sous écoulement des suspensions colloïdales de particules non-sphériques : cas des argiles naturelles

Abstract : We focussed our interest on the flow behaviour of colloidal suspensions of natural swelling clays. Such systems are strongly anisotropic since the disk-shaped particles in suspensions display an average diameter around 200 nm with a thickness close to 1 nm. Under flow, and for very low volume fractions (around 1%), these materials display remarkable mechanical properties going from quasi-Newtonian liquid to yield stress gel. In order to understand the mechanisms leading to such macroscopic behaviour, we have set up an experimental device that enables us to perform simultaneously viscosity (in a cylindrical Couette cell) and small angles x-ray scattering measurements. Thanks to this Rheo-SAXS device, we measured the orientational field of strongly anisotropic bi-dimensional particles in shear flow. When no shear is applied (and in the isotropic liquid phase), the particles are randomly oriented and occupy statistically a volume equivalent to that of the sphere of excluded volume encompassing the particle. The stronger is the applied shear stress, the more confined are the disk-like particles and consequently the small amount of fluid trapped in the statistical motion of the particles decreases from that of the sphere of excluded volume to that of an oblate ellipsoid with double anisotropy. Thus, knowing the orientational field of the particles (measured by SAXS) and applying an effective approach as the one suggested by Quemada for hard spheres, we tried to rebuild the shear-thinning behaviour of these suspensions by taking the volume fraction in statistical ellipsoid instead of that of disk-shaped particles
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Adrian-Marie Philippe. Propriétés sous écoulement des suspensions colloïdales de particules non-sphériques : cas des argiles naturelles. Autre. Université de Lorraine, 2013. Français. ⟨NNT : 2013LORR0056⟩. ⟨tel-01749583⟩

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