Torque transmission and dissipation
in a toothless gear
This is an abstract
for a poster to be presented at the
Fifth
Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is
available on the web.
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: [email protected]
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