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Title: Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation

Abstract

Chemisorbed monolayer films are known to possess favorable characteristics for nanoscale lubrication of micro- and nanoelectromechanical systems (MEMS/NEMS). Prior studies have shown that the friction observed for monolayer-coated surfaces features a strong dependence on the geometry of contact. Specifically, tip-like geometries have been shown to penetrate into monolayer films, inducing defects in the monolayer chains and leading to plowing mechanisms during shear, which result in higher coefficients of friction (COF) than those observed for planar geometries. In this work, we use molecular dynamics simulations to examine the tribology of model silica single-asperity contacts under shear with monolayer-coated substrates featuring various film densities. It is observed that lower monolayer densities lead to reduced COFs, in contrast to results for planar systems where COF is found to be nearly independent of monolayer density. This is attributed to a liquid-like response to shear, whereby fewer defects are imparted in monolayer chains from the asperity, and chains are easily displaced by the tip as a result of the higher free volume. This transition in the mechanism of molecular plowing suggests that liquid-like films should provide favorable lubrication at single-asperity contacts.

Authors:
ORCiD logo [1];  [1];  [1]; ORCiD logo [1]
  1. Department of Chemical and Biomolecular Engineering, ‡Multiscale Modeling and Simulation (MuMS) Center, and §Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory-National Energy Research Scientific Computing Center
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1484287
DOE Contract Number:  
AC02-05CH11231
Resource Type:
Journal Article
Journal Name:
Langmuir
Additional Journal Information:
Journal Volume: 33; Journal Issue: 42; Journal ID: ISSN 0743-7463
Country of Publication:
United States
Language:
English

Citation Formats

Summers, Andrew Z., Iacovella, Christopher R., Cummings, Peter T., and MCabe, Clare. Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation. United States: N. p., 2017. Web. doi:10.1021/acs.langmuir.7b02479.
Summers, Andrew Z., Iacovella, Christopher R., Cummings, Peter T., & MCabe, Clare. Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation. United States. doi:10.1021/acs.langmuir.7b02479.
Summers, Andrew Z., Iacovella, Christopher R., Cummings, Peter T., and MCabe, Clare. Fri . "Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation". United States. doi:10.1021/acs.langmuir.7b02479.
@article{osti_1484287,
title = {Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation},
author = {Summers, Andrew Z. and Iacovella, Christopher R. and Cummings, Peter T. and MCabe, Clare},
abstractNote = {Chemisorbed monolayer films are known to possess favorable characteristics for nanoscale lubrication of micro- and nanoelectromechanical systems (MEMS/NEMS). Prior studies have shown that the friction observed for monolayer-coated surfaces features a strong dependence on the geometry of contact. Specifically, tip-like geometries have been shown to penetrate into monolayer films, inducing defects in the monolayer chains and leading to plowing mechanisms during shear, which result in higher coefficients of friction (COF) than those observed for planar geometries. In this work, we use molecular dynamics simulations to examine the tribology of model silica single-asperity contacts under shear with monolayer-coated substrates featuring various film densities. It is observed that lower monolayer densities lead to reduced COFs, in contrast to results for planar systems where COF is found to be nearly independent of monolayer density. This is attributed to a liquid-like response to shear, whereby fewer defects are imparted in monolayer chains from the asperity, and chains are easily displaced by the tip as a result of the higher free volume. This transition in the mechanism of molecular plowing suggests that liquid-like films should provide favorable lubrication at single-asperity contacts.},
doi = {10.1021/acs.langmuir.7b02479},
journal = {Langmuir},
issn = {0743-7463},
number = 42,
volume = 33,
place = {United States},
year = {2017},
month = {9}
}