Observation of surface energy dependence of boundary slippage of EHL films

It is commonly recognized that surface properties can greatly influence boundary slippage behaviors. This paper investigates the dependence of elastohydrodynamic lubrication (EHL) film boundary slippage on surface energy. Experiments were performed under EHL of different surface energy levels. By tracing an entrapped lubricant core in the contact using optical interferometry, boundary slippage is presented by its movement speed. Experimental observations reveal that lubricant can desorb off a wall of low surface energy. When lubricant flows in the Cr–Steel and Cr-DLC gaps, slippage occurs on the Cr surface. On other hand, in the SiO2–Steel and Al2O3-Steel cases, lubricant retains sufficient absorption on the SiO2 and Al2O3 surfaces but detaches from the steel surface. The different slippage behaviors result in two different lubricant transport characteristics. The results may shed a light on further understanding of boundary slippage.