Superlubricity of C₆₀ molecular bearings - effect of interlacated molecular orientation

抄録

The realization of a novel lubric system, making it possible for nano- and micromachines to move easily, has been strongly desired. Such a lubricant can also contribute to moving a variety of macroscopic objects. We have recently developed graphite/C₆₀/graphite sandwiched systems [1], C₆₀ intercalated graphite films [2], and those consisting of alternating close-packed fullerene monolayers and graphite layers [3], which are expected to provide an exciting breakthrough in industrial development. In this paper, the mechanism of superlubricity of graphite/C₆₀/graphite interface is numerically studied using molecular mechanics [4,5].

As a model of the graphite/C₆₀/graphite interface, the close-packed C₆₀ monolayer inserted between two rigid graphite sheets is used. The periodic boundary condition within the (0001) plane is applied to the 1×1 unit cell. For each graphite interlayer distance, the metastable structure of the graphene/C₆₀/graphene interface is calculated by minimizing the total energy using the structural optimization, Polak-Rebiere-type conjugate gradient (CG) method.

First, the simulated interlayer distances of about 1.3 nm are in good agreement with previous experimental results. Next, the frictional feature along the commensurate direction of the graphene/C₆₀ /graphene interface is investigated. It is clarified that the small rotation and elastic contact of C₆₀ molecules are the origins of the superlubricity of the graphene/C₆₀/graphene interface along the commensurate scan direction. Anisotropy of the superlubricity of the C₆₀ bearing system is obtained [4,5]. Furthermore, the effect of the molecular orientation of C₆₀ on the Amonton-Coulomb's law is also studied, which tells us the close relationship between molecular friction and the molecular-scale local structures.

References

[1] K. Miura, S. Kamiya and N. Sasaki, Phys.Rev. Lett. 90, 055509 (2003).

[2] K. Miura, D. Tsuda, and N. Sasaki, e-J. Surf. Sci. Nanotech. 3, 21 (2005).

[3] M. Ishikawa, S. Kamiya, S. Yoshimoto, M. Suzuki, D. Kuwahara, N. Sasaki, and K. Miura, J. Nanomat. 2010, 891514 (2010).

[4] N. Itamura, K. Miura, and N. Sasaki, Jpn. J. Appl. Phys. 48, 060207(R) (2009).

[5] N. Sasaki, N. Itamura, H. Asawa, D. Tsuda, and K. Miura, Tribology Online 7, 96 (2012).