Experimental Study of the Interfacial Slip on Hydrodynamic Lubrication Under Different Wettabilities

This article presents an experimental study about boundary slippage on the film thickness of hydrodynamic lubrication (HL) using a custom-made slider-on-disc bearing testing apparatus. The interfaces with different affinity were obtained by surface energy modification of sliders with various oleophobic coatings, which are characterised by their contact angle (CA) and contact angle hysteresis (CAH). To study the mechanism of interfacial slip on HL under different wettability constraints, the film thickness and velocity profiles under shear were measured using interference and fluorescence photobleached method, respectively. The results showed that the CAH could better characterise the influence of interface effect on the film thickness of HL, which was explained by the correlation between CAH and the interface potential barrier. Furthermore, it was found that the slip velocity increased with lubricant viscosity and shear rate, which can be explained by the spatial heterogeneity of the flow in conformal contact and the critical shear stress slip model.