Structure and dynamics of water at a clay surface from molecular dynamics simulation

Abstract

We report a molecular dynamics study of the structure and dynamics of water at a clay surface. The negative charge of the surface and the presence of surface oxygen atoms perturbs water over two to three molecular layers, while the nature of the counterions (Na(+)or Cs(+)) has only a small effect. In the first molecular layer, approximately half of the water molecules are H-bonded to the surface. We also analyze the H-bond network between surface water molecules. The diffusion of water molecules along the surface is slowed down compared to the bulk case. As far as the orientational order and dynamics of the water dipole are concerned, only the component normal to the clay surface is perturbed. We investigate the surface H-bond formation and dissociation dynamics and their coupling to the release of molecules from the first molecular layer. We introduce a simple kinetic model in the spirit of Luzar and Chandler [Nature, 1996, 379, 55] to allow for a comparison with bulk water dynamics. This model semi-quantitatively reproduces the molecular simulation results and suggests that H-bond formation is faster with the surface than in the bulk, while H-bond dissociation is slower.

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

“…simulations have provided insight into the behavior of water and ions near flat charged surfaces [2,18,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54]. In particular, these simulations have confirmed that ions confined between planar charged surfaces do form ISSC, OSSC, and diffuse swarm species [35] in agreement with most EDL models.…”

Molecular Dynamics Simulations of Turbostratic Dry and Hydrated Montmorillonite with Intercalated Carbon Dioxide

“…On the other hand, in the open environment, the H-bonding of water to a single smectite surface is weaker than H-bonds between water molecules. [59][60][61] The simulations of Na-MMT systems for the 0-2 and 5-2 compositions using the enforced rotation approach demonstrate a rise in the relative potential energy (and d 001 -spacing) upon rotation (not shown). The energy increases even for the 0-2 composition that is found to demonstrate the opposite trend using the position restraint approach.…”

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

“…The number of water layers in the interlayer depends on the nature of the interlayer cations and on the compaction degree (Kozaki et al, 1998;Ferrage et al, 2005). The external surface water structure and properties can be probed by a molecular dynamics study showing significant density oscillations up to three water layers at phyllosilicate mineral surfaces (Greathouse and Cygan, 2006;Wang et al, 2006;Marry et al, 2008;Tournassat et al, 2009b).…”