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Research Article | Open Access

Molecular behaviors in thin film lubrication—Part two: Direct observation of the molecular orientation near the solid surface

Ming GAO1, Haoyu LI1, Liran MA1( ), Yuan GAO1,2, Linwei MA3, Jianbin LUO1( )
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
School of Metallurgy Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
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Abstract

Over the past twenty years, thin film lubrication (TFL) theory has been used to characterize the molecular behaviors in lubrication films thinner than 100 nm, effectively bridging the gap between elastohydrodynamic lubrication and boundary lubrication. Unfortunately, to date, the TFL molecular model proposed in 1996 has not been directly proven by experimental detection. Herein, a method based on surface-enhanced Raman spectroscopy was developed to show both the packing and orienting of liquid molecules in the TFL regime. By trapping liquid crystal molecules between a structured silver surface and a glass surface, molecular ordering states dominated by shear effect and surface effect were successfully distinguished. A nanosandwich structure consisting of an adsorbed layer, an ordered-molecule layer, and a fluid layer was demonstrated. Molecule imaging in TFL was achieved. Our results illustrate the molecular behaviors and lubrication mechanism in nanoconfined films and facilitate the lubrication design of nanoelectromechanical and microelectromechanical systems.

Keywords

thin film lubricationmolecular behaviorsnematic liquid crystalsurface-enhanced Raman spectroscopylubrication theorynanosandwich structure

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Friction
Volume 7 Issue 5,
October 2019
Pages 479-488
DOI: 10.1007/s40544-019-0279-1
Cite this article:
GAO M, LI H, MA L, et al. Molecular behaviors in thin film lubrication—Part two: Direct observation of the molecular orientation near the solid surface. Friction, 2019, 7(5): 479-488. https://doi.org/10.1007/s40544-019-0279-1

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Received: 26 July 2018
Revised: 09 November 2018
Accepted: 13 January 2019
Published: 04 June 2019
© The author(s) 2019

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