Preparation and characterization of ultrathin dual-layer ionic liquid lubrication film assembled on silica surfaces

A novel ultrathin dual-layer film, which contained both bonded and mobile phases in ionic liquids (ILs) layer, was fabricated successfully on a silicon substrate modified by a self-assembled monolayer (SAM). The formation and surface properties of the films were analyzed using ellipsometer, water contact angle meter, attenuated total reflectance Fourier transform infrared spectroscopy, multi-functional X-ray photoelectron spectroscopy, and atomic force microscope. Meanwhile, the adhesive and nanotribological behaviors of the films were evaluated by a homemade colloidal probe. A ball-on-plate tribometer was used to evaluate the microtribological performances of the films. Compared with the single-layer ILs film deposited directly on the silicon surface, the as-prepared dual-layer film shows the improved tribological properties, which is attributed to the special chemical structure and outstanding physical properties of the dual-layer film, i.e., the strong adhesion between bonded phase of ILs and silicon substrate via the chemical bonding with SAM, the interlinked hydrogen bonds among the molecules, and two-phase structure composed of steady bonded phase with load-carrying capacity and flowable mobile phase with self-replenishment property.