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Abstract
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The swelling of Na-Montmorillonite is simulated by Monte Carlo molecular simulations in NPzzT and ?VT ensembles, in two sedimentary basin conditions of 423 K at 750 atm and 483 K at 1050 atm and by using the CLAYFF force field [J. Phys. Chem. B 108, 1255–1266 (2004)]. The CLAYFF force field predicts a one, two-layer stable hydrate under 423 K at 750 atm and a one-layer stable hydrate under 483 K at 1050 atm with the stable basal spacings of 12.54 and 12.44 A°. The adsorbed water molecules are 45.22 and 41.92 per clay layer, with water densities of 0.28 and 0.26 g/cm3 and total energy of 2.11 and
3.65 kcal/mol of water. The predicted structure of Na-Montmorillonite are consistent with those reported in literature for high temperature and pressure conditions, however the results did not indicate a one-layer hydrate as the stable phase under basin conditions of 423 K at 750 atm [Clays Clay Miner. 34, 385 (1986)]. This work allows addressing the issue of the effect of basin condition on the structure of Na-Montmorillonite hydrate.
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