Under conditions of low speed, small viscosity and molecularly smooth tribe-surfaces, the behavior of lubricant film in the nano scale is different from that in elas-tohydrodynamic lubrication (EHL) and boundary lubri...Under conditions of low speed, small viscosity and molecularly smooth tribe-surfaces, the behavior of lubricant film in the nano scale is different from that in elas-tohydrodynamic lubrication (EHL) and boundary lubrication (BL). Due to the size effect, long-range ordered structure of liquid crystal (LC) has great effects on the tribological properties and film-forming mechanism of thin film in the nano scale. The technique of relative optical interference intensity (ROII) was used to investigate nano-tribological properties when cholesteryl LCs are added to hexadecane. The results indicate that the practical film thickness of hexadecane with liquid crystal is 3-5 times as large as that expected from EHL theory in the low speed region. The film thickness increases with the enhancement in polarity and concentration of LC in hexadecane, and external DC voltage. The effective viscosity of lubricant is related to the film thickness and the voltage and it varies from bulk viscosity to several times or tens展开更多
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 lub...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.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant No. 59735110) and the Outstanding Youth Foundation (Grant No. 50025515).
文摘Under conditions of low speed, small viscosity and molecularly smooth tribe-surfaces, the behavior of lubricant film in the nano scale is different from that in elas-tohydrodynamic lubrication (EHL) and boundary lubrication (BL). Due to the size effect, long-range ordered structure of liquid crystal (LC) has great effects on the tribological properties and film-forming mechanism of thin film in the nano scale. The technique of relative optical interference intensity (ROII) was used to investigate nano-tribological properties when cholesteryl LCs are added to hexadecane. The results indicate that the practical film thickness of hexadecane with liquid crystal is 3-5 times as large as that expected from EHL theory in the low speed region. The film thickness increases with the enhancement in polarity and concentration of LC in hexadecane, and external DC voltage. The effective viscosity of lubricant is related to the film thickness and the voltage and it varies from bulk viscosity to several times or tens
基金financially supported by the National Natural Science Foundation of China(51305225,51527901)
文摘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.
