Anisotropic Adsorption of Water Molecules on Kaolinite: A Molecular Dynamic Study

M Lu and YY Zheng, RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A, 97, 3333-3345 (2023).

DOI: 10.1134/S0036024424030154

The diffusion, storage, and seepage of water in clay are closely related to the coupling effect of clay mineral and water molecules. However, the anisotropic adsorption mechanism of kaolinite crystal remains unclear. This study focuses on the microscopic interattraction property of kaolinite and water molecules using molecular dynamics (MD) simulation method. Three nano-scale kaolinite-water models were established to investigate the adsorption behavior of six surfaces with pore water. According to the interaction energy of clay-water, the adsorption of four edge surfaces is significantly greater than that of two basal surfaces. The anisotropic adsorption characteristics mainly stem from different atomic arrangements along different crystal orientations, forming different electrostatic adsorption and hydrogen bonding effects. Then, the adsorption topological structure of six surfaces was deeply characterized. From the density and potential energy distribution of pore water, the surfaces of kaolinite can adsorb one layer of strongly bound water and weakly bound water. Besides, the diffusion coefficient of water molecules decreases with the increase of the micro-specific surface area of kaolinite crystal, which is consistent with the macroscopic experimental results.

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