Superlubricity

In recent years, the search for superlubric materials has become a subject of practical importance, which may be most evident in the development of miniaturized systems, where nanoscopic surfaces slide past one another. In many cases, friction and wear are the main impediments to miniaturizing such devices even further. Identifying or designing superlubric materials may 

Tangney et al.92 studied the friction between an inner and an outer carbon nanotube. Realistic potentials were used for the interactions within each nanotube and LJ potentials were employed to model the dispersive interactions between nanotubes. The intra-tube interaction potentials were varied and for some purposes even increased by a factor of 10 beyond realistic para-meterizations, thus artificially favoring the onset of instabilities and friction. Two geometries were studied, one in which inner and outer tubes were commensurate and one in which they were incommensurate. 

From the application point of view, reduction of friction is often the primary goal. For many macroscopic technical applications, lubrication is extremely effective and a broad basis of empirical knowledge exists. However, with increasing importance of micromechanical systems and nanotechnology, new concepts for reduction of friction have to be developed. In microelectromechanical systems (MEMS) with high surface-to-volume ratio, stiction and friction become critical issue, that limit 

If friction requires a certain commensurability of the sliding surface, should friction not vanish in almost all situations It would be a coincidence if two surfaces have a similar lattice constant and are aligned. There are several reasons why this is not the case  

Most theories of structural superlubricity are based on the Prandtl-Tomlinson model or the more advanced Frenkel-Kontorova model [1043, 1044], in which the single atom/tip is replaced by a chain of atoms coupled by springs. However, Friedel and de Gennes [1045] noted recently that correct description of relative sliding of crystalline surfaces should include the motion and interaction of dislocations at the surfaces. This concept was taken up by Merkle and Marks [1045] and generalized using the well-established coincident site lattice theory and dislocation drag from solid-state physics. 

Dynamic Superiubricity It is the reduction of friction by vertical osdllations. It is a known phenomenon for macroscopic friction, where it is related to intermittent loss of contad. This requires relatively strong oscillation excitations and is therefore of limited applicability. For nanoscale friction, a marked reduction of friction for 

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The demonstration that superlubricity is possible, at least from a theoretical standpoint, indicates that solids are not required to exhibit friction under all conditions. However, virtually all surfaces exhibit friction as a result of various mechanisms that lead to deviations from the conditions necessary... 

Based on the discussion in earlier sections of this chapter, one may expect atomically flat incommensurate surfaces to be superlubric. Indeed the first suggestion that ultra-low friction may be possible was based on simulations of copper surfaces.6,7 Furthermore, the simulations of Ni(100)/(100) interfaces discussed in the previous section showed very low friction when the surfaces were atomically flat and misoriented (see the data for the atomically flat system between 30° and 60° in Figure 21). In general, however, it is reasonable to assume that bare metals are not good candidates for superlubric materials because they are vulnerable to a variety of energy dissipation mechanisms such as dislocation formation, plastic deformation, and wear. 

Leven I, Kiepel D, Shemesh O, Hod O (2013) Robust superlubricity in graphene/h-BN heterojunctions. J Phys Chem Lett 4 115-120... 

Lee, S. Spencer, N. D. Achieving Ultralow Friction by Aqueous, Brush-Assisted Lubrication. In Superlubricity, Erdemir A., Jean-Michel Martin, J.-M., Eds. Elsevier Amsterdam, 2007 Chapter 21. 

Lee, S., Spencer, N.D. Achieving ultralow friction by aqueous, brush-assisted lubrication. In Erdemir, A., Martin, J.M. (eds.) Superlubricity, pp. 365-396. Elsevier, Amsterdam (2007)... 

As a consequence of the superlubrication potential, a hydrophobic texture could significantly modify squeeze film drainage between surfaces. It is of obvious practical interest to minimize the hydrodynamic resistance, F, to the approach of surfaces. 

K. Falk, F. Sedlmeier, L. Joly, R. R. Netz, and L. r. Bocquet, Molecular origin of fast water transport in carbon nanotube membranes superlubricity versus curvature dependent friction. Nano Lett, 10, 4067 [2010],... 

Superlubricity (friction coefQcient below 0.01) was only observed under UHV or an inert environment. Two different mechanisms can involve this phenomenon ... 

Yuansheng J and Shenghua Li, Superlubricity of in-situ generated protective layer on worn metal surfaces in presence of Mg6Si40io(OH)g, in Superlubricity (Eds A. Erdemir and J.M. Martin), Elsevier, 2007, pp.447-471. 

Polarization happens at sites with even lower atomic CN, which gives rise to the non-zero spin (carrier of topologic insulator), conductor-insulator transition, surface plasmonic enhancement, and the superhydrophobicity, superfluidity, superlubricity, and supersolidity. 

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