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Title: Poly(alkyl methacrylate) Brush-Grafted Silica Nanoparticles as Oil Lubricant Additives: Effects of Alkyl Pendant Groups on Oil Dispersibility, Stability, and Lubrication Property

This paper reports on the synthesis of a series of poly(alkyl methacrylate) brush-grafted, 23 nm silica nanoparticles (hairy NPs) and the study of the effect of alkyl pendant length on their use as oil lubricant additives for friction and wear reduction. The hairy NPs were prepared by surface-initiated reversible addition–fragmentation chain transfer polymerization from trithiocarbonate chain transfer agent (CTA)-functionalized silica NPs in the presence of a free CTA. We found that hairy NPs with sufficiently long alkyl pendant groups (containing >8 carbon atoms, such as 12, 13, 16, and 18 in this study) could be readily dispersed in poly(alphaolefin) (PAO), forming clear, homogeneous dispersions, and exhibited excellent stability at low and high temperatures as revealed by visual inspection and dynamic light scattering studies. Whereas poly(n-hexyl methacrylate) hairy NPs cannot be dispersed in PAO under ambient conditions or at 80 °C, interestingly, poly(2-ethylhexyl methacrylate) hairy NPs can be dispersed in PAO at 80 °C but not at room temperature, with a reversible clear-to-cloudy transition observed upon cooling. High-contact-stress ball-on-flat reciprocating sliding tribological tests at 100 °C showed significant reductions in both the coefficient of friction (up to 38%) and wear volume (up to 90% for iron flat) for transparent, homogeneous dispersionsmore » of hairy NPs in PAO at a concentration of 1.0 wt % compared with neat PAO. Finally, the formation of a load-bearing tribofilm at the rubbing interface was confirmed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.« less
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  1. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry
  2. Univ. of California, Merced, CA (United States). Dept. of Mechanical Engineering
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
  4. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Science Division
Publication Date:
Grant/Contract Number:
AC05-00OR22725; EE0006925
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 9; Journal Issue: 29; Journal ID: ISSN 1944-8244
American Chemical Society (ACS)
Research Org:
Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
Contributing Orgs:
Univ. of California, Merced, CA (United States)
Country of Publication:
United States
36 MATERIALS SCIENCE; antiwear; colloidal stability; friction reduction; hairy nanoparticles; lubricant additives; oil solubility; surface-initiated RAFT polymerization
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1430640