title: Rheo-SAXS investigation of shear-thinning behaviour of very anisometric repulsive disc-like clay suspensions.
abstract: Aqueous suspensions of swelling clay minerals exhibit a rich and complex rheological behaviour. In particular, these repulsive systems display strong shear-thinning at very low volume fractions in both the isotropic and gel states. In this paper, we investigate the evolution with shear of the orientational distribution of aqueous clay suspensions by synchrotron-based rheo-SAXS experiments using a Couette device. Measurements in radial and tangential configurations were carried out for two swelling clay minerals of similar morphology and size, Wyoming montmorillonite and Idaho beidellite. The shear evolution of the small angle x-ray scattering (SAXS) patterns displays significantly different features for these two minerals. The detailed analysis of the angular dependence of the SAXS patterns in both directions provides the average Euler angles of the statistical effective particle in the shear plane. We show that for both samples, the average orientation is fully controlled by the local shear stress around the particle. We then apply an effective approach to take into account multiple hydrodynamic interactions in the system. Using such an approach, it is possible to calculate the evolution of viscosity as a function of shear rate from the knowledge of the average orientation of the particles. The viscosity thus recalculated almost perfectly matches the measured values as long as collective effects are not too important in the system.
authors.affiliation: Laboratoire d'Energétique et de Mécanique Théorique et Appliquée, Nancy University-CNRS, UMR 7563, Vandœuvre Lès Nancy, France. adrian-marie.philippe@ensem.inpl-nancy.fr
authors.forename: A M
authors.initials: AM
authors.lastname: Philippe
authors.forename: C
authors.initials: C
authors.lastname: Baravian
authors.forename: M
authors.initials: M
authors.lastname: Imperor-Clerc
authors.forename: J
authors.initials: J
authors.lastname: De Silva
authors.forename: E
authors.initials: E
authors.lastname: Paineau
authors.forename: I
authors.initials: I
authors.lastname: Bihannic
authors.forename: P
authors.initials: P
authors.lastname: Davidson
authors.forename: F
authors.initials: F
authors.lastname: Meneau
authors.forename: P
authors.initials: P
authors.lastname: Levitz
authors.forename: L J
authors.initials: LJ
authors.lastname: Michot
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry*; D000077215:Clay; D003198:Computer Simulation; D057446:Hydrodynamics; D010316:Particle Size; D012212:Rheology; D053838:Scattering, Small Angle; D033081:Shear Strength; D013535:Suspensions / Q000737:chemistry*; D014783:Viscosity; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D000538:Aluminum Silicates; D013535:Suspensions; D014867:Water; C010863:beidellite; D001546:Bentonite; D000077215:Clay