Necip Güven, 1992. "Molecular Aspects of Clay-Water Interactions", Clay-Water Interface and its Rheological Implications, P. F. Low, J. K. Mitchell, G. Sposito, H. van Olphen, N. Güven, R. M. Pollastro
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The objective of this chapter is to acquaint the reader with the molecular concepts of clay-water interactions that are pertinent for understanding the hydration, swelling, and rheological behavior of clays. In this regard, the topics of special importance are colloidal characteristics of the clay particles, hydration reactions of clays and ions, the interparticle forces in aqueous media, the molecular configuration of the clay/water interface, and the stability of clay suspensions. Fundamentals of colloid chemistry are described in detail in numerous text books; the most recent are the monographs by Hiemenz (1986), Hunter (1987), and Everett (1988). These monographs discuss colloid chemistry at intermediate, advanced, and introductory levels, respectively. Comprehensive accounts of colloid chemistry devoted to the clays are presented by van Olphen (1977), Yariv and Cross (1979), and Sposito (1984).
Aqueous clay suspensions can be considered as a system of four components: clay particles, water molecules, cations (counterions), and anions (coions). These components determine the rheological and colloidal behavior of the clay suspension in various ways depending on their structural, electrical, and other physical characteristics. The contribution of each component is related to its intrinsic characteristics and to its interaction with the other three components. With this in mind, we will first examine the colloidal properties of clay particles, then the structure of a water molecule and the hydration of ions. Subsequently, the hydration of clays and the behavior of aqueous clay suspensions will be treated as the total interaction between these components. The description of clay particles will be
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Clay-Water Interface and its Rheological Implications
Rheology is the science of the flow of fluids and deformation of solids. Of special interest to the clay scientist are the flow behavior and stability of clay suspensions, and the time-dependent deformation of clays in a solid or semi-solid state. The physical state of a clay may change with increasing water content; from a solid, to a semi-rigid plastic, then to a gel, and finally to a suspension. In each state, the main factors determining the rheological behavior of the system are related to: (a) the molecular configuration and dynamics of the clay-water interface, and (b) the nature of the particle interactions at this interface. The hydration of the ions and the clay surfaces plays a special role in clay rheology because flow and deformation directly involve molecular movements along the clay-water interface.