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Dry and in situ (fluid-cell) Atomic Force Microscopy (AFM) and Low-Pressure Gas Adsorption experiments were used to investigate the surfaces of pure Na-smectite particles. These two techniques permit the identification of different surfaces of the platelets (lateral, basal, and interlayer surfaces) and to quantify their surface area. Calculation of the surface area was done for AFM, by measuring directly the dimensions of the clay particles on AFM images, and for gas adsorption experiments, by applying the Derivative Isotherm Summation (DIS) procedure designed by Villiéras et al. (Villiéras et al. 1992, 1997a, 1997b).

In the present study, we find a discrepancy between measurements of the basal and interlayer surface area. This difference is due to the stacking of platelets in dry conditions compared to their dispersion in aqueous suspension. A particle is estimated to be formed of nearly 20 stacked layers in the …