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

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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.

          Author and article information

          Contributors
          Journal
          Friction
          Friction
          Tsinghua University Press (Beijing/Hong Kong )
          2223-7704
          2223-7690
          01 October 2019
          01 October 2019
          : 7
          : 5
          : 479-488
          Affiliations
          [1] 1State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
          [2] 2School of Metallurgy Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
          [3] 3School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
          Author notes
          *Corresponding authors: Liran MA, E-mail: maliran@ 123456mail.tsinghua.edu.cn ; Jianbin LUO, E-mail: luojb@ 123456mail.tsinghua.edu.cn
          Article
          s40544-019-0279-1
          10.1007/s40544-019-0279-1
          3ff74494-0d80-43de-994a-715c7149acdc
          Copyright © Journals of Tsinghua University Press

          This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 Unported License (CC BY-NC 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. See https://creativecommons.org/licenses/by-nc/4.0/.

          History
          : 26 July 2018
          : 09 November 2018
          : 13 January 2019
          Categories
          Research Articles

          Materials technology,Materials properties,Thin films & surfaces,Mechanical engineering
          lubrication theory,thin film lubrication,molecular behaviors,nematic liquid crystal,surface-enhanced Raman spectroscopy,nanosandwich structure

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