The structure configuration, hydrated behavior of counterions, structure properties and diffusion features of water molecules in the interlayer of lithium montmorillonite were investigated by molecular force field and molecular dynamics simulation (MD). The configuration optimization results of molecular force field showed that the layer spacing, density and volume were related to the water content in the interlayer of lithium montmorillonite. The animated trajectory of molecular dynamics simulation demonstrated that the positions of Li^＋ ions in the interlayer of lithium montmorillonite were related with interlayer charge sites in clay sheets. The results of mean square displacement (MSD) and self-diffusion coefficients illustrated that the diffusion of counterions and water molecules were restricted to the surface of clay sheets when in one- and two-layer hydrates of lithium montmorillonite. In the three-layer hydrates, the Li^＋ ions and water molecules became detached from the surface and began quickly diffused towards the other direction. The analysis results of radial distribution function (RDF) and its structure factor showed that the hydrated shell of Li^＋ ions in one-, two-, and three-layer hydrates were different. The structure properties of water molecules in the interlayer of lithium montmorillonite indicated that water molecules were differentiated with molecules and free water molecules, and the ratio of them differed in one-, two- and three-layer hydrates.

Key words: lithium-montmorillonite, molecular force field, molecular dynamics, self-diffusion coefficient, radial distribution function