Comparative study of the monolayers A3Si(CH2)nOCOCH3 (A = Cl,OH) adsorpted on silica surface

Ab-initio density functional theory calculations have been carried out on the grafting of two different chains organosilane compounds on SiO2 hydroxylated solid surfaces. The silica surface is modeled by a Si12O14H24 trydimite based molecule. The organosilane chains to be grafted to the surface are the trihydroxysilanes and the trichlorosilanes with only few alkyls chains. The calculations have been performed with hybrid density functional (B3-LYP/6-31 + G**). Two final products are obtained and are stabilized with two types of interaction: a covalent bond SiOSi on one side of the chain and a hydrogen bond HO … O on the other side of the chain so that the chain lies flat to the surface. The electronic and geometrical properties of these grafted systems are studied. These results give new insight about the grafting of long chains organosilane on silica surfaces.