Superlubricity under ultrahigh contact pressure enabled by partially oxidized black phosphorus nanosheets

Superlubricity has recently raised an increasing interest owing to its great potential in energy saving and environmental benefits. Yet how to obtain stable superlubricity under an ultrahigh contact pressure (>1 GPa) still remains a challenge. Here, we demonstrate that robust liquid superlubricity can be realized even under a contact pressure of 1193 MPa by lubrication with partially oxidized black phosphorus (oBP) nanosheets. The analysis indicates that the oBP nanosheets that absorb large amounts of water molecules are retained at the friction interface and transform the friction pairs interface to that between the oBP nanosheets. Molecular dynamics simulation demonstrates that water molecules could be retained at the friction interface even under the ultrahigh contact pressure owing to the abundant P=O and P–OH bonds formed on the oBP nanosheet surfaces, contributing to the achievement of stable superlubricity under the ultrahigh contact pressure. This work has the potential of introducing the liquid superlubricity concept in diverse industrial applications involving high-contact-pressure operating conditions.

Achieving Macroscale Liquid Superlubricity Using Lubricant Mixtures of Glycerol and Diols

Friction and wear are ubiquitous in moving mechanical systems, and achieving vanishing friction and wear could significantly improve energy efficiency and extend the service life of mechanical components. In this paper, various diols, viz. ethylene glycol (EG), 1,3-propanediol (13-PD), and 1,2-propdiol (12-PD), have been selected to be mixed with glycerol for superlubricity performance. The results show that the lubricant mixture of EG and glycerol (EG/glycerol) and the mixture of 13-PD and glycerol (13-PD/glycerol) are effective in providing superlow friction (COF < 0.01) for steel tribopairs under ambient atmosphere environment with little surface damage caused. However, 12-PD, which exhibits the same chemical formula as 13-PD except for the configuration of hydroxyl groups, is ineffective for superlubrication. Furthermore, compared with 13-PD, EG is more efficient in preparing superlubric lubricants. Experimental and molecular dynamics simulation results show that the superlow friction realized by the lubricant mixtures of glycerol and diols is related to their intermolecular hydrogen-bonding interaction and the adsorbed formation of adsorbed molecular layers. The intermolecular interaction could affect the rheological property of lubricant mixtures and the hydrodynamic lubricant film-forming capability at the interface, while the quality of the adsorbed molecular layers determines the passivating efficiency for asperity interactions between opposite surfaces. Due to the atomic structure difference, EG is the most desirable diol for this objective, followed by 13-PD, while 12-PD is ineffective. These findings could help enable the rational design of novel lubricants for superlubricating performance and push the development of liquid superlubricity for future engineering applications.

Achieving Macroscale Liquid Superlubricity Using Lubricant Mixtures of Glycerol and Diols

BackgroundWe aimed to assess a serological biopsy using five stomach-specific circulating biomarkers pepsinogen I (PGI), PGII, PGI/II ratio, anti- Helicobacter pylori (H. pylori) antibody, and gastrin-17 (G-17) for identifying high-risk individuals and predicting risk of developing gastric cancer (GC).ResultsIn the cross-sectional analysis, PGII, the PG ratio, G17, anti- H. pylori IgG were associated with the presence of CAG, and the five biomarkers combined prediction is more effective than single factor prediction (0.692 vs 0.54, 0.604, 0.616, 0.629).ConclusionThe combination of pepsinogens, G17 and anti-H. pylori antibodies for serological analysis is helpful to screen CAG high-risk individuals from the general population and recommend that these people should carry out further endoscopy and biopsy.