Preparation and Microtribological Properties of Self-assembling Composite Films on Silicon Substrate

Self-assembling composite monolayers of 3-aminopropyl triethoxysilane (APS) and dodecyl trimethoxysilane (WD-10) were coated on the surface of silicon substrate by coadsorption method. Molecular dynamics was used to simulate the interfacial binding energy of the mixed system at elevated temperatures and under different molecule ratios. And nine different experimental conditions were designed by orthogonal design according to the simulation results. The surface morphologies, wettability and chemical composition of SAMs were characterized by atomic force microscopy, contact angle tester and X-ray photoelectron spectroscopy, the results showed that silane molecules were successfully fabricated on the surface of the hydroxylated silicon substrate and the best quality of the SAMs was obtained at 25 ℃ for assembly temperature, 4 h for assembly time and 6 for the pH of the solution. Besides, the microtribological properties of SAMs were evaluated on a microtribometer and the worn surface were investigated by scanning electron microscope. Compared with the hydroxylated substrate, the SAMs caused boundary lubrication effect and reduced the friction and wear on the surface of the specimens. And the lowest friction coefficient and smallest width of wear were achieved at 1:1 for the ratio of APS to WD-10.