Static and Kinetic Friction of Smooth Glass Surfaces Rubbed With Silicone Oils

The study of the effect of waiting time, loading and unloading on static and kinetic friction for real contact micro-systems was carried out. Three types of silicone fluid with the viscosity of 100, 450 and 5000 cSt at 25° C were used. Stop-start experiments allowed us to estimate the relaxation time after the static friction overshoot. For silicone liquid with viscosity of 100 cSt, relaxation of friction force (F) after the static friction overshoot occurred over one cycle of testing. Relaxation of F for fluids with the viscosity of 450 and 5000 cSt occurred during a long time and this effect was opposite for these silicone liquids. The analysis of loading-unloading cycles showed only a partial reversibility of F. The results were compared with static friction and stick-slip data obtained in other works, using SFA and FFM techniques. In order to explain the effect of viscosity and structure of the lubricant layers on stick-slip phenomenon, interior and wall slip of the lubricant film is discussed.