Nanoscale simulation of Na-Montmorillonite hydrate under basin conditions, application of CLAYFF force field in parallel GCMC

Abstract

The swelling of Na-Montmorillonite is simulated by Monte Carlo molecular simulations in NP_zzT and μVT 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 Å. 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.

Keywords:

• Monte Carlo simulation
• Na-Montmorillonite
• CLAYFF force field
• grand canonical ensemble
• basin condition

Acknowledgements

We are thankful to Mr A.M. Moslemi from Foroozan Danesh Lian scientific research company for his support. We are also thankful to Research and Technology Department, National Iranian Oil Company for its financial support.