Molecular Dynamics Study on the Wetting Behavior of Kaolinite Surfaces

Abstract

Kaolinite is a layered silicate clay mineral whose surface wettability plays a crucial role in soil hydrological processes and environmental remediation. In this study, molecular dynamics (MD) simulations are employed to systematically investigate the wetting behavior of water droplets on two representative (001) kaolinite crystal surfaces: the hydrophilic Al–O octahedral surface and the hydrophobic Si–O tetrahedral surface. The analysis includes energy evolution, mean square displacement (MSD), radial distribution function (RDF), quantitative hydrogen-bond statistics, and contact angle measurement of droplet profiles to reveal the underlying wetting mechanisms. Results show that the Al–O surface exhibits complete wetting due to cooperative hydrogen bonding between surface hydroxyl groups and water molecules, whereas the Si–O surface demonstrates significant hydrophobicity. Moreover, droplet size is found to affect interfacial stability and wetting; larger droplets produce more stable and uniform adsorption layers, while the smaller droplets exhibit greater fluctuations and less ordered interfacial water structures, demonstrating significant size-dependent wetting effects. This study not only quantitatively analyzes the hydrophilicity/hydrophobicity of kaolinite surfaces, but also provides microscopic insights into how hydrogen bonding, molecular diffusion, and multilayer adsorption collectively govern interfacial wetting. These findings offer theoretical guidance for understanding clay mineral interfacial hydrology and potential engineering applications.