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Slip of alkanes confined between surfactant monolayers adsorbed on solid surfaces

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Title: Slip of alkanes confined between surfactant monolayers adsorbed on solid surfaces
Authors: Ewen, JP
Kannam, S
Todd, B
Dini, D
Item Type: Journal Article
Abstract: The slip and friction behaviour of n-hexadecane, confined between organic friction modifier (OFM) surfactant films adsorbed on hematite surfaces, have been studied using nonequilibrium molecular dynamics (NEMD) simulations. The influence of OFM type and coverage, as well as the applied shear rate and pressure have been investigated. A measurable slip length is only observed for OFM films with a high surface coverage, which provide smooth interfaces between well-defined OFM and hexadecane layers. Slip commences above a critical shear rate, beyond which the slip length first increases with increasing shear rate and then asymptotes towards a constant value. The maximum slip length increases significantly with increasing pressure. Systems and conditions which show a larger slip length typically give a lower friction coefficient. Generally, the friction coefficient increases linearly with logarithmic shear rate; however, it shows a much stronger shear rate dependency at low pressure than at high pressure. Relating slip and friction, slip only occurs above a critical shear stress, after which the slip length first increases linearly with increasing shear stress and then asymptotes. This behaviour is well described using the extended molecular kinetic theory (MKT) slip model. This study provides a more detailed understanding of the slip of alkanes on OFM monolayers. It also suggests that high coverage OFM films can significantly reduce friction by promoting slip, even when the surfaces are well-separated by a lubricant.
Issue Date: 14-Mar-2018
Date of Acceptance: 14-Mar-2018
URI: http://hdl.handle.net/10044/1/58043
DOI: https://dx.doi.org/10.1021/acs.langmuir.8b00189
ISSN: 0743-7463
Publisher: American Chemical Society
Start Page: 3864
End Page: 3873
Journal / Book Title: Langmuir
Volume: 34
Issue: 13
Copyright Statement: © 2018 American Chemical Society. 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.
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Engineering and Physical Sciences Research Council
Engineering and Physical Sciences Research Council
Royal Society
Funder's Grant Number: EP/N025954/1
CASE Studentship
IES\R3\170233
Keywords: Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
NONEQUILIBRIUM MOLECULAR-DYNAMICS
AA FORCE-FIELD
BOUNDARY-CONDITION
STEARIC-ACID
FRICTION MODIFIER
LIQUID SLIP
THIN-FILMS
SHEAR-FLOW
WALL SLIP
N-ALKANES
MD Multidisciplinary
Chemical Physics
Edition: 13
Publication Status: Published
Online Publication Date: 2018-03-14
Appears in Collections:Faculty of Engineering
Mechanical Engineering
Faculty of Natural Sciences



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