Molecular behaviors in thin film lubrication—Part two: Direct observation of the molecular orientation near the solid surface
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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.
Keywordsthin film lubrication molecular behaviors nematic liquid crystal surface-enhanced Raman spectroscopy lubrication theory nanosandwich structure
The work was financially supported by the National Natural Science Foundation of China (51305225, 51527901).
Ming GAO, Liran MA, and Jianbin LUO conceived and designed the study. Ming GAO performed the main experiments and Linwei MA fabricated the SERS substrate. Ming GAO, Haoyu LI, Liran MA, and Yuan GAO wrote the manuscript. Ming GAO, Liran MA, and Jianbin LUO reviewed and edited the manuscript. All the authors read and approved the manuscript.
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