Abstract
Advanced lubrication is essential in human life for improving mobility, durability, and efficiency. Here we report the synthesis, characterization, and evaluation of two groups of oil-suspendable silver nanoparticles (NPs) as candidate lubricant additives. Two types of thiolated ligands, 4-(tert-butyl)benzylthiol (TBBT) and dodecanethiol (C12), were used to modify Ag NPs in two size ranges, 1-3 and 3-6 nm. The organic surface layer successfully suspended the Ag NPs in a poly-alpha-olefin (PAO) base oil with concentrations up to 0.19-0.50 wt %, depending on the particle type. Use of the Ag NPs in the base oil reduced friction by up to 35% and wear by up to 85% in boundary lubrication. The two TBBT-modified NPs produced a lower friction coefficient than the C12-modified one, while the two larger NPs (3-6 nm) had better wear protection than the smaller one (1-3 nm). Results suggested that the molecular structure of the organic ligand might have a dominant effect on the friction behavior, while the NP size could be more influential in the wear protection. No mini-ball-bearing or surface smoothening effects were observed in the Stribeck scans. Instead, the wear protection in boundary lubrication was attributed to the formation of a silver-rich 50-100 nm thick tribofilm on the worn surface, as revealed by morphology examination and composition analysis from both the top surface and cross section.
| Original language | English |
|---|---|
| Pages (from-to) | 37227-37237 |
| Number of pages | 11 |
| Journal | ACS Applied Materials and Interfaces |
| Volume | 9 |
| Issue number | 42 |
| DOIs | |
| State | Published - Oct 25 2017 |
Funding
The authors thank A.G. Bro from ExxonMobil for providing the PAO base oil and appreciate D. Coffey from ORNL for preparation of TEM samples. Research was supported by the Vehicle Technologies Program ( DE EE0006925), Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE). Electron microscopy characterization was performed at ORNL’s Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division, Office of DOE-BES. Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
| Funders | Funder number |
|---|---|
| LLC | |
| ORNL’s | |
| Office of DOE-BES | |
| Scientific User Facilities Division | |
| UT-Battelle | |
| U.S. Department of Energy | |
| Office of Energy Efficiency and Renewable Energy | |
| Vehicle Technologies Program | DE EE0006925 |
Keywords
- additive
- antiwear
- boundary lubrication
- friction reduction
- lubricant
- silver nanoparticles
- tribofilm