Initial hydration characteristics of dry montmorillonite and insights for water transport mechanisms in nanochannels

Abstract

The early stages of the hydration process in dehydrated montmorillonite (MMT) are crucial for understanding the transition mechanisms between different hydration states of clay minerals. While X-ray Diffraction (XRD) experiments and models provide a macroscopic understanding of the hydration processes of clay minerals, there is still a lack of microscopic models for the transition processes of hydration states, making understanding these transitions at the molecular scale a challenging issue. In this study, molecular dynamics simulations were used to analyze the initial hydration process of water molecules in the dry interlayers of MMT, the mechanisms of their transport, and the influencing conditions. It was found that hydroxyl (–OH) groups formed at the edges of clay particles hinder the entry of water molecules into the montmorillonite channels. Additionally, the properties such as water flux, pressure, and potential energy of the channels were calculated. It was found that the initial hydration process of montmorillonite is influenced by initial conditions such as size, velocity, temperature, interlayer cation type, and number of cations. Entrance effects, exit effects, and disturbances of water molecules were also observed during the initial hydration process. An increase in the ratio of the inlet and outlet sizes of the montmorillonite channel reduces the entrance/exit effect on the density, velocity, and number of water molecules transported, affecting the path of motion of the water transport. In addition, it was found that the number, size, and position of interlayer cations can have a perturbing effect on water molecule transport. The results of this study can be used for the preparation and development of high-precision nanomontmorillonite, the permeation assessment of nuclear waste barriers, and the development of nano-MMT films.