Nonequilibrium molecular dynamics simulations of organic friction modifiers adsorbed on iron oxide surfaces
File(s)
Published version
Accepted version
Author(s)
Ewen, JP
Gattinoni, C
Morgan, N
Spikes, H
Dini, D
Type
Journal Article
Abstract
For the successful development and application of lubricants, a full understanding of the nanoscale behavior of complex tribological systems is required, but this is difficult to obtain experimentally. In this study, we use nonequilibrium molecular dynamics (NEMD) simulations to examine the atomistic structure and friction properties of commercially relevant organic friction modifier (OFM) monolayers adsorbed on iron oxide surfaces and lubricated by a thin, separating layer of hexadecane. Specifically, acid, amide, and glyceride OFMs, with saturated and Z-unsaturated hydrocarbon tail groups, are simulated at various surface coverages and sliding velocities. At low and medium coverage, the OFMs form liquidlike and amorphous monolayers, respectively, which are significantly interdigitated with the hexadecane lubricant, resulting in relatively high friction coefficients. At high coverage, solidlike monolayers are formed for all of the OFMs, which, during sliding, results in slip planes between well-defined OFM and hexadecane layers, yielding a marked reduction in the friction coefficient. When present at equal surface coverage, OFMs with saturated and Z-unsaturated tail groups are found to yield similar structure and friction behavior. OFMs with glyceride head groups yield significantly lower friction coefficients than amide and particularly carboxylic acid head groups. For all of the OFMs and coverages simulated, the friction coefficient is found to increase linearly with the logarithm of sliding velocity; however, the gradient of this increase depends on the coverage. The structure and friction details obtained from these simulations agree well with experimental results and also shed light on the relative tribological performance of these OFMs through nanoscale structural variations. This has important implications in terms of the applicability of NEMD to aid the development of new formulations to control friction.
Date Issued
2016-05-10
Date Acceptance
2016-04-11
Citation
Langmuir: the ACS journal of surfaces and colloids, 2016, 32 (18), pp.4450-4463
ISSN
0743-7463
Publisher
American Chemical Society
Start Page
4450
End Page
4463
Journal / Book Title
Langmuir: the ACS journal of surfaces and colloids
Volume
32
Issue
18
Copyright Statement
This is an open access article published under a Creative Commons Attribution (CC-BY)
License, which permits unrestricted use, distribution and reproduction in any medium,
provided the author and source are cited.
License, which permits unrestricted use, distribution and reproduction in any medium,
provided the author and source are cited.
License URL
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (E
Shell Research Limited
Engineering and Physical Sciences Research Council
Identifier
https://pubs.acs.org/doi/10.1021/acs.langmuir.6b00586
Grant Number
EP/G026114/1
EP/N50869X/1
See further information
CASE Studentship
Subjects
Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
ATOM FORCE-FIELD
FATTY-ACIDS
BOUNDARY LUBRICATION
MIXED LUBRICATION
OIL INTERFACE
CHAIN-LENGTH
MODEL
ADSORPTION
FILMS
MONOLAYERS
Chemical Physics
Publication Status
Published
Date Publish Online
2016-04-26