Covalent grafting of alkyl chains on laser-treated titanium surfaces through silanization and phosphonation reactions

This work evaluates the efficiency of silanization and phosphonation reactions for the grafting of alkyl chains on the surface of titanium treated by nanosecond laser. The light blue squama-like oxide layers with dominating anatase and rutile were obtained. The silanization using alkoxysilanes with C12 and C18 alkyl chains was attempted in tetrahydrofuran, in pure liquid phase and in vapor phase. The phosphonation with octylphosphonic acid was performed in boiling water solutions. The obtained surfaces were characterized by Raman and X-ray photoelectron spectrometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Their hydrophobicity was evaluated using static contact angle measurements.The modification in pure liquid silane and in vapor phase allowed obtaining high loadings (6 and 10 at.% Si respectively) of grafted groups and the formation of polycondensed silane layers. The silanization in tetrahydrofuran resulted in partial monolayer coverage. The phosphonation in boiling water solutions allowed obtaining significant P loading (up to 7 at.%) and full monolayer coverage. Both silanization and phosphonation increased the hydrophobicity of laser-treated surfaces. However, the modification with octylphosphonic acid in water solutions is more appropriate since milder conditions of chemical functionalization and lower concentrations of the modifier are necessary to obtain similar organic loading and hydrophobicity.