Effects of Interfacial Contact Characteristics on the Friction Properties of Ooctadecyltrichorosilane and 3-Aminopropyltrimethoxysilane Self-Assembled Monolayers

The effects of interfacial contact characteristics on the friction properties of octadecyltrichorosilane (OTS) and 3-aminopropyltrimethoxysilane (APS) self-assembled monolayers (SAMs) were investigated on a universal micro-tribometer by sliding the SAMs against vacuum-deposited Cu or Ni coating at various sliding velocities and normal loads. At the same time, Lennard-Jone potential was used to compare the interaction between the Cu or Ni coating and the SAMs of OTS and APS. The results indicated that the friction coefficients of the Ni coating sliding against both the OTS and APS SAMs were larger than those of the Cu coating sliding the two SAMs under the same test conditions. This was attributed to the stronger interaction between the Ni coating and the two SAMs. The friction coefficients of the Cu and Ni coatings sliding against the OTS SAM increased with increasing sliding velocity and decreased with increasing load. Moreover, the Cu coating sliding against the APS SAM recorded a decreased friction coefficient with increasing sliding velocity, while the Ni coating sliding against the APS SAM had an increased friction coefficient with increasing sliding velocity but a reduced one with increasing load. The differences in the friction behaviors of the OTS and APS SAMs against the Cu and Ni coatings were related to the different relaxation behaviors of the SAMs and the different interactions among the SAMs and the metallic coatings as the counterparts.