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Computer simulation of the structure and dynamics of phenol in sodium montmorillonite hydrates

Monte Carlo and molecular dynamics computer simulations have been used to study the structure and dynamics of phenol‐water solutions in the bulk and confined within the interlayer pores of sodium montmorillonite clays, as a function of pressure and temperature. Conditions have been chosen to mimic those encountered at burial depths of up to 6 km, thereby enabling us to shed light on subsurface processes including groundwater contamination and oil and gas migration. The structural data show that the phenol molecules are able to form a donor hydrogen bond to the clay surface. In addition, the phenolic –OH group is solvated by approximately three water molecules, and is also able to coordinate directly to an interlayer sodium cation. The phenolic aromatic ring is surrounded by approximately 25 water molecules in the bulk, compared to 18 in the compacted clay. Interlayer diffusion increases by an order of magnitude as temperature is increased from 275 K to 460 K. However, diffusion decreases by a factor of 2–4 as we move from the bulk into a clay hydrate of layer spacing ∼17 Å. For example, at 275 K the diffusion coefficient of phenol is 8.3 × 10−10 m2 s−1 in bulk solution, compared to 2.5 × 10−10 m2 s−1 in the clay.