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The three-dimensional structure of large packings of monosized spheres with volume fractions ranging between 0.58 and 0.64 has been studied with x-ray computed tomography. We search for signatures of organization, classifying local arrangements and exploring the effects of local geometrical constrains on the global packing. This study is the largest and the most accurate empirical analysis of disordered packings at the grain-scale to date, mapping over 380,000 sphere coordinates with precision within 0.1% of the sphere diameters. We discuss topological and geometrical methods to characterize and classify these systems emphasizing the implications that local geometry can have on the mechanisms of formation of these amorphous structures. Some of the main results are (1) the observation that the average number of contacts increases with the volume fraction; (2) the discovery that these systems have a very compact contact network; (3) the finding that disordered packing can be locally more efficient than crystalline packings; (4) the observation that the peaks of the radial distribution function follow power law divergences; (5) the discovery that geometrical frustration plays no role in the formation of such amorphous packings.

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Interactions between charged surfaces immersed in aqueous calcium solutions were measured using the surface force apparatus and the atomic force microscope. With the surface force apparatus, good agreement with previously reported measurements was found for mica surfaces in dilute solutions up to 0.1 M. However, at higher concentrations large discrepancies were observed. Compared to the earlier work, the strength of the force was lower by two or three orders of magnitude and the range was diminished. Experiments using the atomic force microscope indicated similar force-distance profiles for the interaction between silicon nitride and mica. With this technique concentrations as high as 5 M can be investigated, and owing to the small radius of curvature much higher pressures can be recorded. Results obtained by both methods confirm that the force is strongly attractive at very small surface separations, in agreement with the theoretical predictions based on calculations of ion correlations. Just outside of that interval the interaction is repulsive, and it can be quantitatively explained by taking into account the adsorption of hydrated ions onto the surface (sign reversal of the effective surface charge) and the layering of co- and counterions. At larger surface separations, the behavior indicates a balance between the double layer repulsion and the van der Waals attraction (the presence of a secondary minimum).