Mussel-Inspired Interfacial Modification for Ultra-Stable MoS2 Lubricating Films with Improved Tribological Behavior on Nano-Textured ZnO Surfaces Using the AACVD Method

Anisotropic Stick-Slip Frictional Surfaces via Titania Nanorod Patterning

Nanoscale or microscale surface texturing is an effective technique to tailor the tribological properties between two surfaces that are rubbed against each other. In order to achieve the desired frictional properties by a patterned surface, one needs an in-depth understanding of the underlying mechanisms. Here, we demonstrate anisotropic stick-slip friction achieved via a nanotextured surface of tilted titania nanorods (TiNRs). The surface was developed by using the glancing angle deposition (GLAD) technique, and exhibited load-dependent variations in stick-slip friction as well as frictional anisotropy in different sliding directions. For studying the frictional properties of the newly developed surface, lateral force microscopy (LFM) was performed in three different reciprocal orientations (0° rotated, 45° rotated, 90° rotated) using a custom-made colloidal alumina atomic force microscopy (AFM) probe. The frictional behavior was found to vary significantly with the orientation. At 0° rotated position) a prominent "stick-slip" was observed when scanning opposite to the tilt direction, whereas the phenomenon reduced significantly when the nanotextured surface was scanned along the tilt direction or rotated to different angles (45 and 90°) with respect to the sliding direction of the AFM cantilever supporting the probe. The experimental findings were interpreted based on the classical solution for large deflections of tilted elastic rods. Overall, the textured surface, LFM-based frictional measurement, and the quantitative analysis presented here provide a fundamental understanding of how friction can be significantly varied on a surface patterned with tilted TiNRs at a length scale of about 1 μm, which can be comprehensively applied to nanorod patterns of other materials on different substrates.

Compaction of Hydrophobic Molybdenum Disulfide Coatings for Promoting Tribological Behaviors on Engineering Steel

Ambient environment has a crucial effect on the lubrication performance of molybdenum disulfide (MoS₂) coatings. In this work, we fabricated porous MoS₂ coatings via a facile optimized aerosol-assisted chemical vapor deposition (AACVD) method. It is found that the obtained MoS₂ coating demonstrates outstanding antifriction and antiwear lubrication performance with the coefficient of friction (COF) and wear rate as low as 0.035 and 3.4 × 10^-7 mm³/Nm in lower humidity (15 ± 5)%, respectively, which is comparable to the lubrication ability of pure MoS₂ in vacuum. In addition, the hydrophobic property of porous MoS₂ coatings is suitable for infusing lubrication oil to achieve stable solid-liquid lubrication in higher humidity (85 ± 2)%. The composite lubrication system shows excellent tribological behavior in both dry and wet environments, which will alleviate the sensitivity of the MoS₂ coating to the environment and ensure the service life of the engineering steel in complex industrial backgrounds.

A Biomimetic Lubricating Nanosystem with Responsive Drug Release for Osteoarthritis Synergistic Therapy

Osteoarthritis (OA) is associated with lubrication failure of articular cartilage and severe inflammatory response of joint capsule. Synergistic therapy combining joint lubrication and anti-inflammation emerges as a novel treatment of OA. In this study, bioinspired by ultralow friction of natural articular synovial fluid and mussel adhesion chemistry, a biomimetic nanosystem with dual functions of enhanced lubrication and stimuli-responsive drug release is developed. A dopamine mediated strategy realizes one step biomimetic grafting of hyaluronic acid (HA) on fluorinated graphene. The polymer modified sheets exhibit highly efficient near-infrared absorption, and show steady lubrication with a long time under various working conditions, in which the coefficient of friction is reduced by 75% compared to H₂ O. Diclofenac sodium (DS) with a high loading capacity of 29.2% is controllably loaded, and responsive and sustained drug release is adjusted by near-infrared light. Cell experiments reveal that the lubricating nanosystem is taken up by endocytosis, and anti-inflammation results confirm that the nanosystem inhibits osteoarthritis deterioration by upregulating cartilage anabolic gene and downregulating catabolic proteases and pain-related gene. This work proposes a promising biomimetic approach to integrate polymer modified fluorinated graphene as a dual-functional nanosystem for effective synergistic therapy of OA.