Molecular dynamics simulation of water molecules absorption by different cations based Montmorillonite

Abstract

Using molecular mechanics and molecular dynamics (MD) methods, Li-, Na-, K-, Ca- cations based montmorillonite models are built in materials studio software. Molecular dynamic simulations are carried out to investigate the influences of different cations on the swelling behavior of montmorillonite when absorbing water. Molecular dynamic simulations indicate that the montmorillonite's volume and layer spacing are increased by multi-steps, but the density is reduced by multi-steps. Water molecule concentration profiles in lithium-, sodium-, potassium- and calcium-montmorillonite adsorption models show that the montmorillonite can form one, two and three layers of water molecules. The radial distribution function of Li-, Na-, K-, Ca- cations based montmorillonite is obtained for absorbing 16 to 96 water molecules. The results indicate Li+ is easier to hydrate, follows by Na+, while K+ and Ca2+ are not easy to hydrate. Different types of cations between layers have different effects on the adsorption ability of montmorillonite.