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Torque transmission and dissipation in a toothless gear

Deepak Srivastava^a, Sumio Iijima^b and Boris I. Yakobson*

Physics Department, North Carolina State University
^aComputational Nanotechnology at NAS Systems Division of NASA Ames Research Center/MRJ, Moffett Field, CA 94035-1000
^bNEC R&D Group, 34 Miyukigaoka, Tsukuba, Ibaraki 305, Japan

This is an abstract for a poster to be presented at the Fifth Foresight Conference on Molecular Nanotechnology.

In spite of many similarities between the macroscopic prototypes and their nanoscale analogs, "small is different". How different -- can often be studied in atomistic computer simulations. For instance, a contact between two atomically smooth macroscopic cylinders allows almost no torque transmission between them. In contrast, in the nanoscale their surfaces are "rough", and van der Walls attraction becomes an important component. This is an interesting idea - will the gear [1,2] work just by virtue of the van der Waals interactions, without any designed teeth? We will present experimental HRTEM images of two carbon nanotubes forming a "toothless gear". We will assess theoretically the cohesion and torque transmission between them. Both continuum macro-scale estimates and the explicit molecular dynamics simulation will be presented. In simulation the C-C interaction is modeled by Brenner's analytic potential within the graphene layers, and by a standard "6- 12" Lennard-Jones for van der Waals forces between the layer within the same tube, or between the different tubes in contact. The inter-axial distance is relaxed, which corresponds to "natural" normal force between the tubes attracted to each other in this scale (an indication of this attraction is the noticeable tube flattening). We observe acceleration of the tube driven by the rotation of another. Energy transmission is less efficient due to the softness of graphene layers and substantial dissipation in their constant bending (internal friction). Role of the temperature, number of layers and the diameters of the tubes will be discussed.

References
[1] J. Han, A. Globus, R. Jaffe, G. Deardorff, Nanotechnology v. 8, 95 (1997).
[2] D. Srivastava, Nanotechnology, submitted (1997).

*Corresponding Address:
Boris I. Yakobson, Physics Department, North Carolina State University, Raleigh, NC 27695, Phone: (919)-515-2426, FAX: (919)-515-7331, E-Mail: yakobson@ncsu.edu
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