Molecular simulation of wetting behavior on hydroxylation and silanization SiO2 surface

Key words:  interface  silica  hydroxylation  silanization  molecular simulation

Abstract:

The microscopic wetting behavior of water on silica surface was investigated by molecular dynamics simulation, in which the hydroxylation surface and silanization surfaces with different alkyl chain length were considered. And the wetting mechanism was analyzed using interaction energy, radial distribution function and diffusion coefficient. It is observed that the hydroxylation surface has strong hydrophilicity. However, the silanization surface exhibits hydrophobicity, and the hydrophobicity is enhanced with lengthened alkyl chain. Also the results indicate that the water cluster has strong interaction with hydroxylation silica surface, which makes the water molecules in the bottom of cluster move towards surface preferentially. In this way the pre-absorbed water molecules would promote the adsorption of the rest water molecules. Then, the water cluster spreads completely on hydroxylation silica surface, and exhibits strong hydrophobicity. On the contrary, the interaction between water cluster and silanization SiO₂ surface is mainly originated from van der Waals potential, which cannot overcome the hydrogen-bond interaction between water cluster, and presents strong hydrophobicity. With the increase of alkyl chain length, the van der Waals potential between water cluster and silanization surface becomes weak, and the hydrophobicity is improved.