Nanofriction and Nanowear of Sliding Systems: Simulations of Nanocoating Effect
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It has been shown that the mechanisms of friction and wear on the nanometer scale can be absolutely different from their micrometer or larger scale counterparts. It was found that friction stress is constant and of the order of the theoretical shear strength, when a sliding contact size is small. However, at a critical contact size, there is a transition beyond which the frictional stress decreases with increasing contact size, until it reaches a second transition where the friction stress gradually becomes independent of the contact size. Hence, the mechanisms of slip are size-dependent, or in other words, there exists a scale effect. This phenomenon is not observed in larger scale contacts.
Making use of such understanding of tribology on the nanometer scale, recent developments in nanotechnology have revealed wondrous potential in modifying surfaces on the nanometer scale. By observing lizard's feet, researchers have proven that clusters of nanometer scale contacts can provide strong adhesion just like the spatula at the ends of the hairs on a lizard's feet that allow them to walk on walls and ceilings. On the other hand, based on nanostructures of the surfaces of lotus leaves, engineered surfaces with the right surface energy and nanoscopic bumps can ensure that dust particles do not stick to the surface easily, hence resulting in self-cleansing capabilities.