Biomimetic joints inspired soft and hard combined 2D diamond solvent-free nanofluids with multi-layer structure for superior lubrication

Abstract

The articulating joints consist of a three-layer lubricating structure, which combines soft and hard materials, including cartilage, polymer brushes, and a hydration layer. This structure leverages the synergistic effects of fluid and boundary lubrication to maintain ultra-low friction under different pressures on the same frictional surface. In this study, a biomimetic multilayer lubricating structure inspired by joint tissues is constructed using single-crystalline diamond nanosheets (SCND) as the hard phase material. Through a facile chemical reduction method and employing polydopamine (PDA) as a "bridge", a soft phase material is deposited onto the SCND surface to produce diamond composite silver nanocomposites (SCND@PDA@Ag). Subsequently, two solvent-free SCND@PDA@Ag nanofluids are prepared by grafting organic canopy substances onto the SCND@PDA@Ag surface via ionic bonds or covalent bonds, referred to as SCND@PDA@Ag-ionic bonding nanofluid and SCND@PDA@Ag-covalent bonding nanofluid, respectively. The findings reveal that the SCND@PDA@Ag-covalent bonding solvent-free nanofluid exhibits superior lubricating performance for steel/SiC contacts. The friction coefficient and wear rate for steel/SiC are significantly reduced by 93.2 % and 63.1 %, respectively, compared to dry friction, it's noteworthy that these results outperform those achieved by individual components of the lubricant. During the friction process, SCND and silver particles on the surface of SCND@PDA@Ag-covalent bonding solvent-free nanofluid work together to enhance lubrication synergistically. Furthermore, silver particles on the surface of SCND are released and fill into the worn surface, providing a repairing effect. This study highlights that the design of soft-hard multilayer structures offers a novel approach for researching nanocomposite materials in the field of tribology.