Chemically functionalized polymer nanoparticles reduce friction on steel surfaces
Mineral oil lubricants protect engine parts from wear, and this
effect is enhanced by adding polymer nanoparticles to the lubricating
oil. A UK team has now discovered that epoxy functionalization of these
nanoparticles further promotes friction reduction on metal surfaces. As
the team reports in the journal Angewandte Chemie, nanoparticles
containing epoxy groups adhere strongly to stainless steel surfaces,
which leads to a significant reduction in friction.
© Wiley-VCH, re-use with credit to ‘Angewandte Chemie’ and a link to the original article.
Automotive engines comprising well lubricated parts consume less
fuel, produce lower emissions, and suffer less long-term wear. Mineral
oil is widely used as a lubricant, and nanoparticles can be directly
prepared within this solvent using a technique known as
polymerization-induced self-assembly. Coating the surface of the metal
components with nanoparticles of a few dozen millionths of a millimeter
in size protects them from direct contact.
Csilla György and Steve Armes at the University of Sheffield (UK)
designed “hairy” nanoparticles comprising oil-soluble poly(lauryl
methacrylate) chains and an oil-insoluble nanoparticulate core. These
nanoparticles were made to stick strongly to metal surfaces by
introducing epoxy groups into the “hairs” by copolymerizing lauryl
methacrylate with glycidyl methacrylate, an epoxy-functional monomer.
The team found that the epoxy-bearing nanoparticles reacted with
hydroxy groups located at the surface of stainless steel. This reaction
led to strong adhesion of the nanoparticles, a phenomenon known as
chemical adsorption. Whether chemical adsorption occurred or not
depended on the precise location of the epoxy groups. “To our surprise,
introducing a far larger number of epoxy groups into the nanoparticle
cores had no beneficial effect,” explains Armes.
The adsorbed nanoparticles reduced friction significantly, as the
Sheffield team discovered when conducting tribological studies in
collaboration with scientists at Lubrizol, an engine oil additives
company based in the UK. “Remarkably, the adsorbed nanoparticles
remained intact on the stainless steel surface after such experiments,
which were conducted at the typical operating temperature of an internal
combustion engine,” Armes adds.
Such epoxy-functionalized nanoparticles could therefore mean a
further leap in performance for lubricant additives for next-generation
engine oil formulations.
About the Author
Prof. Steven P.
Armes, FRS, is the Firth Professor of Chemistry and Professor of Polymer
and Colloid Chemistry at the Department of Chemistry of the University
of Sheffield, UK. His research team combines living radical
polymerization techniques with polymerization-induced self-assembly to
prepare block copolymer nanoparticles for a wide range of applications.