PEGylated carbon black as lubricant nanoadditive with enhanced dispersion stability and tribological performance

Poly(ethylene glycol) (PEG) chains were covalently grafted onto carbon black (CB) using a PEG-terminated trimethoxysilane, yielding PEGylated CB additives (CB-SiPEG) with different SiPEG contents. Unlike pristine CB, CB-SiPEG was readily dispersed in PEG200 base oil, with CB-SiPEG hydrodynamic particle sizes being considerably smaller than those of pristine CB. At optimal SiPEG content, friction coefficient and specific wear rate in ball-on-disk tribometer tests were reduced by 35% and 67% respectively, with 1% wt. CB-SiPEG compared to PEG200 alone. In contrast, pristine CB, alone or with unbound SiPEG, did not show friction-reducing or antiwear capacity. Disk analysis supports CB-SiPEG surface deposition forming a protective tribofilm. Hydrodynamic particle size and lubricating performance of CB-SiPEG/PEG200 blends were preserved after 6 months, indicating high dispersion stability.