Characterization and tribological investigation of self-assembled MPTS-MPTES/RE composite films

γ-mercapto-propyl trimethoxysilane (MPTS) and γ-methacryloxy propyltrimethoxysilane (MPTES) were self-assembled on a hydroxylated glass substrate to form a two-dimensional organic monolayer (MPTS-MPTES SAM). The terminal thiol groups (–SH) in the MPTS-MPTES SAM were in-situ oxidized into sulfonic acid groups (–SO3H) to endow the film with good chemisorption ability. Then rare earth (RE) (lanthanum-based) composite thin films were prepared by self-assembly technique based on the as-prepared SAM, taking advantage of the chemisorption ability of the sulfonic acid groups. Automatic force microscope (AFM), X-ray photoelectron spectrometry (XPS), contact angle measurement and ellipsometer were used to characterize MPTS-MPTES/RE composite films. The macrofriction and wear behaviors of the films sliding against an AISI-52100 steel ball were examined on a unidirectional friction and wear tester, and the worn surface morphologies were observed on an AFM. The results showed that MPTS-MPTES/RE films had a low friction coefficient (0.09) and a long wear life (5980 sliding pass) at a light load (50 mN). It indicated that the superior tribological properties of the MPTS-MPTES/RE composite films were attributed to the special characteristic of RE elements, the mobility of the films and good bonding strength.