Ab Initio Molecular Dynamics Study of a Monomolecular Water Layer on Octahedral and Tetrahedral Kaolinite Surfaces

The structure and dynamics of a monomolecular water layer on the octahedral and tetrahedral surfaces of the kaolinite layer have been investigated using short-time ab initio molecular dynamics. The arrangement and the structure of the water layer differ significantly on both surfaces. On the octahedral side the water layer forms relatively strong hydrogen bonds with the surface hydroxyl groups. This interaction significantly influences the layout of the water molecules in this case. On the other hand, the water molecules on the tetrahedral surface have the tendency to aggregate, forming hydrogen bonds among themselves. Only weak hydrogen bonds with the basal oxygen atoms of the tetrahedral surface are formed. Thus, the octahedral and tetrahedral surfaces of the kaolinite layer are of different chemical nature and can be considered as hydrophilic and hydrophobic, respectively.