Molecular Dynamics Simulation of Diffusion and Electrical Conductivity in Montmorillonite Interlayers

Abstract

The diffusion of water and ions in the interlayer region of smectite clay minerals represents a direct probe of the type and strength of clay−fluid interactions. Interlayer diffusion also represents an important link between molecular simulation and macroscopic experiments. Here we use molecular dynamics simulation to investigate trends in cation and water diffusion in montmorillonite interlayers, looking specifically at the effects of layer charge, interlayer cation and cation charge (sodium or calcium), water content, and temperature. For Na-montmorillonite, the largest increase in ion and water diffusion coefficients occurs between the one-layer and two-layer hydrates, corresponding to the transition from inner-sphere to outer-sphere surface complexes. Calculated activation energies for ion and water diffusion in Namontmorillonite are similar to each other and to the water hydrogen bond energy, suggesting the breaking of water−water and water−clay hydrogen bonds as a likely mechanism for interlayer diffusion. A comparison of interlayer diffusion with that of bulk electrolyte solutions reveals a clear trend of decreasing diffusion coefficient with increasing electrolyte concentration, and in most cases the interlayer diffusion results are nearly coincident with the corresponding bulk solutions. Trends in electrical conductivities computed from the ion diffusion coefficients are also compared.

Layer Charge Effects on Adsorption and Diffusion of Water and Ions in Interlayers and on External Surfaces of Montmorillonite

“…Furthermore, in a given hydration state or in the mesopore, the isosteric heats are found to be similar for all counterions. are generally consistent with experiments 14,17 and previous simulation results 27,30 (see, for example, Table S2). The quasi-elastic neutron scattering techniques are suitable to study water dynamics on the scales which can also be probed by MD simulations.…”

“…This fact suggests a higher mobility of water associated with the monovalent ions than with the divalent ions. 28,30 However, there are exceptions, e.g., water is less mobile in the 1W hydration state of Li-montmorillonite possibly due to the presence of inner-sphere surface complexes. Interestingly, in the presence of CO 2 , the water diffusion is more restricted in Cs-montmorillonite when compared to K-montmorillonite.…”

Mechanism Associated with Kaolinite Intercalation with Urea: Combination of Infrared Spectroscopy and Molecular Dynamics Simulation Studies

“…Molecular dynamics simulation is an effective tool for characterizing interactions between chemicals and mineral surfaces. 19–23 Such simulations can reproduce experimental results, and provide a direct atomic-level view of the interactions involved in the intercalation, which cannot be obtained from empirical evidence or spectroscopic analysis. In previous computational studies, the molecular dynamics simulations were only used to gain insight into the conformation of small molecules in kaolinite interlayers, 24–26 and adsorption energies of intercalated chemicals on kaolinite surfaces were calculated using quantum methods in relatively simple model systems.…”

Molecular simulation of interfacial reaction between TiAl alloy melts and different coatings

“…The Ti-48Al model whose lattice parameters are a=b=4.10 Å, c=4.18 Å; α=β=γ=90° [17] was built with the Amorphous Cell module of the Materials Studio. Then, after its energy was optimized (see Fig.1), this model was piled into the amorphous units with the specified density and periodic boundary conditions.…”