Abstract
This article reports on improved lubricating performance by combining oil-soluble poly(lauryl methacrylate) brush-grafted silica nanoparticles (hairy NPs or HNP) and an oil-miscible phosphonium-phosphate ionic liquid (IL) as a friction-reducing additive for a polyalphaolefin (PAO) oil. The HNP was synthesized by surface-initiated reversible addition-fragmentation chain transfer polymerization. At a total concentration of 2% and sufficiently high individual concentrations for HNP and IL in PAO, high-contact stress, ball-on-flat reciprocating tribological tests showed that the friction decreased by up to 23% compared with 2% HNP alone in PAO and by up to 35% compared to the PAO mixed with 2% IL. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis revealed that the tribofilm formed from the PAO containing 1% HNP + 1% IL was enriched with both Si and P, indicating that both hairy NPs and IL were involved in the tribochemical reactions. In addition, the O 1s and Si 2p peaks in the core-level XPS spectra exhibited significant shifts for the mixture of 1% HNP + 1% IL compared to those for 2% HNP, suggesting the possible formation of new covalent bonds. These results indicated that HNP and IL reacted with each other and also with the metal substrate during the rubbing process, which likely strengthened the tribofilm and its bonding with the substrate and thus further improved the lubrication.
| Original language | English |
|---|---|
| Pages (from-to) | 15129-15139 |
| Number of pages | 11 |
| Journal | ACS Applied Materials and Interfaces |
| Volume | 10 |
| Issue number | 17 |
| DOIs | |
| State | Published - May 2 2018 |
Funding
The work was supported by a grant from US Department of Energy, Office of Energy Efficiency and Renewable Energy, and Vehicle Technologies Office (DE EE0006925). SEM−EDS was performed at the JIAM Microscopy Center of the University of Tennessee Knoxville, and the authors thank Dr. John Dunlap for his assistance. XPS was performed at the IEN/IMAT Materials Characterization Facility at the Georgia Institute of Technology in Atlanta, Georgia, and the authors thank Walter Henderson for his assistance.
| Funders | Funder number |
|---|---|
| US Department of Energy | |
| Office of Energy Efficiency and Renewable Energy | DE EE0006925 |