Synthesis of polyelectrolyte-decorated polydopamine nanoparticles via surface reconstruction for enhancing oil-based lubrication

Polydopamine nanoparticles (PDA NPs) show bright prospects in the field of lubricant additives due to their high interface adhesion and reaction properties. However, the synthesis of PDA NPs with excellent dispersibility and lubricity in lubricating oils remains a great challenge. In this work, a class of polyelectrolyte-decorated PDA NPs (PPDA NPs) were synthesized by surface reconstruction of PDA NPs. The lipophilic PPDA NPs can be stabilized in PEG200 base oil without any sediments over 6 months. Compared with PEG200 base oil, the PPDA NPs (1.0 wt%)/PEG200 dispersion not only reduced the friction coefficient (COF) by 37.3 % and wear volume by 51.6 % but also performed well under heavy loads, high speeds, and long duration. Wear surface analyses confirmed that the structural evolution from PPDA NPs to nanosheets induced the formation and deposition of hybrid tribofilm with robust tribological behaviors, enabling desirable oil lubrication. Overall, the synergistic effects between PDA cores and PPDA shells contributed to the superior lubricity of PPDA NPs. This study provides a promising protocol for designing and synthesizing oil-dispersible PPDA NPs, brightening the application prospect of organic polymer NPs in tribology.