Preparation and tribological properties of polymer film covalently bonded to silicon substrate via an epoxy-terminated self-assembled monolayer

A covalently immobilized polymer film was constructed on silicon substrate by a two-step method. As an anchor interlayer, (3-glycidoxypropyl)trimethoxysilane (GPMS) was self-assembled on hydroxylated silicon substrate to create epoxy-terminated surface, then poly(styrene-b-acrylic acid) (PSAA) was chemically grafted to the epoxy-derivatized substrates. The formation and surface properties of the films were characterized by means of ellipsometry, water contact angle measurement, attenuated total reflectance Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, and atomic force microscope (AFM). The nano- and micro-tribological properties of the films were evaluated by AFM and ball-on-plate tribometer, respectively. The results show that GPMS–PSAA film exhibits excellent durability and wear resistance, which is attributed to the molecular components of PSAA and the firm bonding between polymer molecules and silicon substrate via epoxysilane molecular glue. The influence of interlayer between polymer and substrate surface on tribological properties of ultrathin polymer film was revealed, which has an important significance upon designing ultrathin lubrication films with excellent tribological properties for micro/nanoelectromechanical systems.