Studies On The Efect Of Interface Affinity On Hydrodynamic Thin Film Lubrication

With the progress of interface science,liquid film lubrication has been being re-recognized in the tribological design of sliding contacts of miniature devices,where interface affinity plays a very important role.In the meaning time,advanced surface modification technology has facilitated the preparation of interfaces with different affinity,including those surfaces with heterogeneous affinity.The present project is mainly focused on the influences of interface affinity on the hydrodynamic lubrication.The main research work includes:(1)Anti-finger-print oil(AF)and fluoroalkysilane(FAS)were used to modify the slider surface to get low surface energy.Some of sliders were modified by AF in such a way to achieve different affinity to lubricants in the inlet and outlet areas of a slider.(2)Aqueous glycerol solutions with the same viscosity as PAOs were prepared and various interface affinities can thus be obtained through combining different liquid and surfaces.For these interfaces film thicknesses were measured by a fixed-incline slider-bearing tester.The results showed that the contact angle and contact angle hysteresis,which are generally used to measure the interface affinity,cannot always correlate well to the film thickness.Alternatively,adhesion work seems to match the film thickness better for the lubricants which have the same viscosity but different affinity to the solid surface.(3)Film thickness was measured for slider surfaces with heterogeneous affinity to lubricants.Under a wedged parallel gap,the results showed that the slippage step effect can work well to produce lubricating film.Under a general wedge gap,it was seen that a slider with heterogeneous surface affinity could induce low film thickness,which is attributed to the side leakage in the area of low affinity despite of the slippage step effect.(4)Aparallel micro-gap was obtained by the use of a hydrodynamically lubricated step slider and the results showed that different interface affinity can make the film thickness different.It was also found that the decrease of film thickness by AF modification was influenced markedly by the applied load,and it was thought that the load increase could promote the slippage and therefore induces a smaller film thickness.(5)The change of film thickness with boundary yield stress was calculated based on the boundary yield stress model under difference working conditions.By comparing the test results with the calculation,the relationship between the boundary yield stress and the sliding speed was obtained.