Exchange of (3-mercaptopropyl)trimethoxysilane with alkanethiol and co-adsorption on silver powder

The saturated adsorption of the (3-mercaptopropyl)trimethoxysilane (SHC3H6Si(OCH3)3, 3-MPT) self-asemblied monolayers (SAMs) on silver powder was firstly determined. A quantitative analysis of 3-MPT suggests that there is a lower saturation adsorption than that of 1-octadecanethiol (C18H37SH) on Ag at room temperature. The exchange reaction of C18H37SH replacing 3-MPT at different temperatures indicates that a great quantity of 3-MPT on the surface remains unexchangable. The study on co-adsorption reaction of two thiols shows that only 3-MPT adsorption is diffusion-controlling course at the early stage at lower temperature, while others display a thermodynamical controlling process. The ratio of C18H37SH to 3-MPT (C18H37SH/SHC3H6Si(OCH3)3) at co-adsorption equilibrium on surface is around 2.3 in the experimental temperature range. Contact angle measurements support the above results and show that the self-assemblied mixed monolayer (SAMM) formed by two thiols was better order in higher temperature.