Recent evidence of the widespread occurrence of beidellite in soils around the world necessitates a better understanding of the role of charge location on the behavior of this smectite as compared to the more studied montmorillonites. This study focuses on the role of charge and charge location on the microstructure of smectite gels, the colloidal stability and sorption of a nonionic polymer by smectites, and wetting and drying of these smectites as seen by X-ray diffraction and infrared spectroscopy.; After equilibration at a suction pressure of 3.2 kPa before and after a desiccation, TEM observations showed large differences in the microstructure of the Na{dollar}sp+{dollar} beidellite, and both a low and high charge montmorillonite. Monolayers were rare, rather individual layers were organized in particles with larger interparticle distances. This has implication for the theories relating swelling pressures to interlayer distances or surface areas, and implies the need of an understanding of the geometrical organization of particles for the study of swelling in smectites. Location of isomorphous substitution in the tetrahedral sheet of smectites resulted in an increased lateral extension of overlapping layers within particles. This was reflected in a greater capacity to rehydrate after a desiccation. Increased number of layers in particles were found with increasing surface charge density. The geometric organization of the particles, controlled by the surface charge and charge location, is critical to the understanding of the ability of Na{dollar}sp+{dollar} smectite to hold water against an applied suction.; Clay suspension stability and sorption of an organic polymer, two properties sensitive to surface charge characteristics, were selected to examine the differences in colloidal behaviors of these smectites. The pH dependency of the smectites could not be explained based only on edge charge considerations, and it is proposed that tetrahedral charge location enhances the pH effect on the critical coagulation concentration. Decreased poly(vinyl) alcohol sorption with either increasing surface charge or tetrahedral charge location was also observed. Both total surface charge density and charge location affect the ease of replacement of water molecules by PVA on the surface of smectites.; X-ray diffraction of the drying of smectites show that tetrahedral charge retards the transition from a two layer to a one layer hydrate. Rehydration of the montmorillonites went through a series of randomly interstratified intermediates, whereas the beidellite showed a series of segregated structures. Hysteresis was observed both by X-ray diffraction and infrared spectroscopy. Infrared spectroscopy indicated that during wetting a significant portion of the water is initially present in pores. It is hypothesized that the slower rewetting of the interlayer space is retarded by the extension of the particles in the ab plane.; This study shows that the general properties, such as swelling or coagulation, of smectites are similar, but that the degree to which these properties varies greatly with differences in layer charge characteristics.
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