title: Aqueous suspensions of natural swelling clay minerals. 1. Structure and electrostatic interactions.
abstract: In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10(-3) M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order.
authors.affiliation: Laboratoire Environnement et Minéralurgie, Nancy Université-CNRS, UMR 7569, BP40 54501 Vandœuvre Cedex, France. erwan.paineau@ensg.inpl-nancy.fr
authors.forename: Erwan
authors.initials: E
authors.lastname: Paineau
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bihannic
authors.forename: Christophe
authors.initials: C
authors.lastname: Baravian
authors.forename: Adrian-Marie
authors.initials: AM
authors.lastname: Philippe
authors.forename: Patrick
authors.initials: P
authors.lastname: Davidson
authors.forename: Pierre
authors.initials: P
authors.lastname: Levitz
authors.forename: Sérgio S
authors.initials: SS
authors.lastname: Funari
authors.forename: Cyrille
authors.initials: C
authors.lastname: Rochas
authors.forename: Laurent J
authors.initials: LJ
authors.lastname: Michot
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D001688:Biological Products / Q000737:chemistry*; D000077215:Clay; D008970:Molecular Weight; D009997:Osmotic Pressure; D053838:Scattering, Small Angle; D017640:Silicates / Q000737:chemistry; D055672:Static Electricity; D013535:Suspensions; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D001688:Biological Products; D017640:Silicates; D013535:Suspensions; D014867:Water; C524813:laponite; D000077215:Clay