Preparation of well-structured organosilane layers on silica

An efficient grafting process of monofunctional alkylchlorosilanes (general formula: CH3-(CH2)(n-1)-Si(CH3)(2)Cl with n varying from 4 to 30) onto sil ica nanoparticules was developed by varying the surface preparation and the solvent used for the deposition process. A vapor phase deposition method w as considered as reference and silicon wafers with a native SiO2 layer were used as a model surface of the silica particles, The grafting method was e valuated by studying the wettability and the grafting densities of the resu lting monolayers. The chain conformation of the monolayers was determined b y comparing the thickness measured by SE ellipsometry and ATM. By comparing the solvent and vapor phase deposition methods. it was demonstrated that t he deposition process had a large influence on the structure of the grafted monolayers. The same structure as from a vapor phase method can be obtaine d from a solvent deposition process by a suitable choice of the solvent and by a strict cleaning of the surface before deposition. The grafting of muc h longer chains of such silane-terminated polyethylenes with different mola r mass on the silica surface was also investigated in order to study the ef fects of the chain length on the grafting density and the layer structure. For both the short alkylchlorosilanes and polymeric grafted chains, the pro posed organization of the grafted chains at the silica surface is found to be strongly dependent on the length of the alkyl chains.