We present a study of the adsorption of single molecules of volatiles, such as water, ethanol, ethyl acetate, pyridine, toluene, and n-octane, on the dry surface of a smectite clay using a series of calculations based on density functional theory. Our clay model contains both tetrahedral and octahedral substitutions, and sodium as the counterion. After establishing the accuracy of our calculations for predicting the structural features of known clays, we determine the structural features of our model clay and then characterize the changes induced by molecular adsorption and the dependence of binding on the adsorption site. In all cases, binding energies are higher in configurations bound to cations located above rings with tetrahedral substitution than for those above rings with octahedral substitutions. For molecules containing an electronegative atom, binding energies inversely correlate well with their ionization potential. Our results allow an interpretation of the trend of measured vaporization rates at low coverage and reveal that they correlate inversely with the binding energies of the molecules.

Using calculations based on density-functional theory, we explore the configurations that water molecules (2,3,4;6) assume on the surface a sodium 2:1 smectite clay with isomorphic substitutions both on octahedral and tetrahedral sheets. The hydrophilicity of the surface is inhomogeneous, depending on the specific location of the counterions and of the cation replacements in the siloxane rings. The counterion does not complete the first hydration shell. Adsorption may occur in the form of coexisting monomers, dimers, and trimers, but at the level of six molecules, a water ring bound to two sodium ions becomes the most stable configuration. This structural transition observed for the adsorbate can be seen as marking the onset of the formation of water networks on the clay surface.

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Self-diffusion NMR is used to investigate monodispersed oil in water emulsions and the subsequent gel formed by removing the water through evaporation. The radius of the oil droplets in the emulsions is measured using a number of diffusion methods based on the measurement of the mean squared displacement of the oil, water, and tracer molecules. The results are consistent with the known size of the emulsions. Bragg-like reflections due to the restricted diffusion of the water around the oil droplets are observed due to the low polydispersity of the emulsions and the dense packing. The resulting data are fitted to a pore glass model to give the diameter of both the pools of interstitial water and the oil droplets. In the gel, information on the residual three-dimensional structure is obtained using the short time behavior of the effective diffusion coefficient to give the surface to volume ratio of the residual protein network structure. The values for the surface to volume ratio are found to be consistent with the expected increase of the surface area of monodisperse droplets forming a gel network. At long diffusion observation times, the permeability of the network structure is investigated by diffusion NMR to give a complete picture of the colloidal system considered.