Tribological properties of polyaromatic organics as lubricating grease.

The tribological properties of polyaromatic organics (x P y E) as lubricating grease additives are studied by simulations and experiments. Molecular Dynamics (MD) simulations are used to simulate the mechanical properties of four kinds of polyaromatic organics (2P1E, 3P2E, 4P3E, and 5P4E) with different aromatic ring numbers and a mass fraction under 300 MPa and 5 m/s relative shear velocity of the two solid walls. The friction force, positive pressure, stress, and adsorption energy are calculated quantitatively. Meantime, the friction coefficient of lubricating grease and the wear morphology of the sample are measured by Multifunctional Friction and Wear Testing Machine. The results show that the organic additives adsorbed on the wall form a protective film during the shearing process, improving the bearing capacity and reducing friction and wear. Among them, the 3P2E organic additive has an appropriate number of aromatic rings. Its single molecular adsorption energy and unit adsorption energy are higher than other organic additives and can uniformly lay on the wall to form a stable, protective film. This demonstrates the best friction performance and improves the load-bearing capacity of the lubricating film, reducing maximum wall stress by 53.4 %. • The effect of polyaromatic organics (x P y E) as grease additives is studied. • Molecular length and aromatic ring number of x P y E affect tribological properties. • Mass fraction of x P y E affects the grease friction performance. • The lubrication system containing 2.5 wt% 3P2E shows the best friction performance. • 3P2E can reduce maximum wall stress by 53.4 % and improve load-bearing capacity. [ABSTRACT FROM AUTHOR]