Thermodynamic Origin of Structural Superlubricity: Entropy Matters.
Structural superlubricity, a state of vanishing friction between two incommensurate contact surfaces, is a fascinating phenomenon in modern tribology and shows attractive applications in the fields of sliding devices. Here, we reveal that structural superlubricity intrinsically originates from the configurational entropy of atoms in the incommensurate contact surfaces, based on which, we firstly developed a concise thermodynamic model for the structural superlubricity. The model can universally explain the reported experimental observations in superlubricity very well. Most critically, our model analytically correlates the friction ({\tau}) with sample size (R), twisted angle ({\theta}) and temperature (T) simply as {\tau}=3kTcot({\theta}/2)/(2{\pi}R^3), which not only provides the physical foundation for structural superlubricity, but could also facilitate the development of new superlubric materials as well as extending their applications at extreme temperatures and normal loads.