Aqueous Suspensions of Natural Swelling Clay Minerals. 1. Structure and Electrostatic Interactions

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• 作者：Erwan Paineau ; Isabelle Bihannic ; Christophe Baravian ; Adrian-Marie Philippe ; Patrick Davidson ; Pierre Levitz ; Se虂rgio S. Funari ; Cyrille Rochas ; Laurent J. Michot
• 刊名：Langmuir
• 出版年：2011
• 出版时间：May 3, 2011
• 年：2011
• 卷：27
• 期：9
• 页码：5562-5573
• 全文大小：1299K
• 年卷期：v.27,no.9(May 3, 2011)
• ISSN：1520-5827

文摘

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鈭払oltzmann approach for ionic strength up to 10^鈭? M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson鈭払oltzmann 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.