Lubrication mechanism of a strong tribofilm by imidazolium ionic liquid
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Author(s)
Type
Journal Article
Abstract
Friction modifiers are surface-active additives added to base fluids to reduce friction
between rubbing surfaces. Their effectiveness depends on their interactions with rubbing
surfaces and may be mitigated by the choice of the base fluid. In this work, the
performance of an imidazolium ionic liquid (ImIL) additive in polyethylene-glycol (PEG)
and 1,4-butanediol for lubricating steel/steel and diamond-like-carbon/diamond-like
carbon (DLC-DLC) contacts were investigated. ImIL containing PEG reduces friction
more effectively in steel-steel than DLC-DLC contacts. In contrast, adding ImIL in
1,4-butanediol results in an increase in friction in steel-steel contacts. Results from
Raman spectroscopy, XPS and FIB-TEM reveal that a surface film is formed on steel
during rubbing in ImIL containing PEG. This film consists of two layers. The top layer is
composed of amorphous carbon and are easily removed during rubbing. The bottom layer,
which contains iron oxide and nitride compound, adheres strongly on the steel surface.
This film maintains its effectiveness in a steel-steel contact even after ImIL additives are
2
depleted. Such film is not observed in 1,4-butanediol where the adsorption of ImIL is
hindered, as suggested by QCM measurements. No benefit is observed when the base
fluid on its own is sufficiently lubricious, as in the case of DLC surfaces.
This work provides fundamental insights on how compatibilities among base fluid,
friction modifier and rubbing surface affect performance of IL as surface active additives.
It reveals the structure of an ionic liquid surface film, which is effective and durable. The
knowledge is useful for guiding future IL additive development.
between rubbing surfaces. Their effectiveness depends on their interactions with rubbing
surfaces and may be mitigated by the choice of the base fluid. In this work, the
performance of an imidazolium ionic liquid (ImIL) additive in polyethylene-glycol (PEG)
and 1,4-butanediol for lubricating steel/steel and diamond-like-carbon/diamond-like
carbon (DLC-DLC) contacts were investigated. ImIL containing PEG reduces friction
more effectively in steel-steel than DLC-DLC contacts. In contrast, adding ImIL in
1,4-butanediol results in an increase in friction in steel-steel contacts. Results from
Raman spectroscopy, XPS and FIB-TEM reveal that a surface film is formed on steel
during rubbing in ImIL containing PEG. This film consists of two layers. The top layer is
composed of amorphous carbon and are easily removed during rubbing. The bottom layer,
which contains iron oxide and nitride compound, adheres strongly on the steel surface.
This film maintains its effectiveness in a steel-steel contact even after ImIL additives are
2
depleted. Such film is not observed in 1,4-butanediol where the adsorption of ImIL is
hindered, as suggested by QCM measurements. No benefit is observed when the base
fluid on its own is sufficiently lubricious, as in the case of DLC surfaces.
This work provides fundamental insights on how compatibilities among base fluid,
friction modifier and rubbing surface affect performance of IL as surface active additives.
It reveals the structure of an ionic liquid surface film, which is effective and durable. The
knowledge is useful for guiding future IL additive development.
Date Issued
2023-03-01
Date Acceptance
2022-03-03
Citation
Friction, 2023, 11, pp.425-440
ISSN
2223-7690
Publisher
SpringerOpen
Start Page
425
End Page
440
Journal / Book Title
Friction
Volume
11
Copyright Statement
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License URL
Publication Status
Published
Date Publish Online
2022-06-12