Investigation on growth process and tribological behavior of mixed alkylsilane self-assembled molecular films in aqueous solution

In this paper, we investigated the frictional behaviors of the mixed self-assembled molecular films of the fluoroalkylsilane (FAS) molecules and non-fluoroalkylsilane (n-FAS) molecules with different chain length covalently absorbed on silicon surfaces, characterized by the universal ball-disk UMT-2 experimental tester under aqueous solution conditions. The surfaces of the substrate modified by mixed self-assembled molecular films were examined by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The formation processes of the molecular films were characterized by quartz crystal microbalance (QCM). The results indicated that it would take a longer time to reach the adsorption equilibrium of the molecular films with the increment of carbon chain length. The measured tribological results showed that the mixing of the fluoroalkylsilane and non-fluoroalkylsilane enhance the lubrication and decrease the friction and wear compared to the one-component thin films. This may be caused by the reduced excitation of the energy dissipation channels.

► The water-based lubrication properties of mixed and single component self-assembled molecular films were investigated. ► The adsorption equilibrium of the molecular films is relative to the intermolecular interaction forces and the hydrolysis of C8F. ► The mixing of C8F with C12 and C16 increase the surface tension and reduce the electrical affinity, resulting in the weak hydrophobicity.