Theoretical study on the interactions between silica and the products of 3-mercaptopropyltriethoxysilane (MPTS) with different hydrolysis degrees

Abstract The study of the interactions between silane and silica is of primary importance for revealing the silanization mechanism and optimizing the modification process of silica. In this study, the interactions between precipitated silica and the products of 3-mercaptopropyltriethoxysilane (MPTS) with varying degrees of hydrolysis, before and after the grafting reaction, were systematically investigated in terms of the adsorption energy, adsorption configuration, and electronic detail by density functional theory (DFT). The pathways of the grafting reactions were also investigated. The results show that the silanes with varying hydrolysis degrees were adsorbed flat on the silica surface before the grafting reaction, via dispersion forces and hydrogen bonds. The degrees of hydrolysis strongly affected the type and number of newly formed bonds, which further influenced the adsorption energies and the pathways of the grafting reactions. It is favorable for partially hydrolyzed silanes to graft on the silica surface by eliminating ethanol during the silanization of silica. After grafting, hydrogen bonds are usually formed between the silica surface and the grafted silanes, resulting in the flat adsorption behaviors on the silica surface. The products of reaction (ethanol and water) are also adsorbed on the silica surface via hydrogen bonds.