Molecular dynamics simulation of hydration expansion characteristics of Na-vermiculite

Abstract

In this study, molecular dynamics simulations were used to investigate the changing pattern of Na-vermiculite (Na-VMT) with increasing water content, as well as the swelling characteristics under different hydration states, and to compare with experimental results of other scholars. The simulation results indicate that as the water content in Na-VMT increases, the interlayer space expands, leading to a reduction in the binding force of the clay mineral layer on Na⁺, thus promoting the hydration and diffusion of Na⁺. During the hydration transition of Na-VMT, the interaction between water molecules and Na⁺ ions gradually strengthens, leading some Na⁺ to shift from inner-sphere to outer-sphere coordination. Due to differences in substitution positions and charge density, the interlayer binding force of Na-VMT is stronger than that of Na-montmorillonite (Na-MMT), resulting in fewer outer-sphere coordinated Na⁺ ions, smaller hydration parameters, and lower self-diffusion coefficients for Na-VMT.