Speaker
Astrid de Wijn
(Trondheim University)
Description
The combination of water with graphite or graphene is under
active investigation in several fields for a number of
reasons. In the field of tribology, it is of interest due to
the action of graphite powder as a solid lubricant, which is
far more effective under humid conditions than in vacuum or
dry air. This is opposite to the case for other solid
lubricants, such as WS2 and MoS2 [1]. Moreover, water alone
is a poor lubricant, due to its low viscosity-pressure
co-efficient. While suggestions have been made as to the
reason behind water's beneficial effects on graphite as a
lubricant [2], this effect is not yet understood. We use
atomistic molecular-dynamics simulations to investigate
equilibration of water confined between graphene sheets over
a wide range of pressures.
We demonstrate that, under the right sliding conditions,
square ice can form in an asperity, and that it is similar
to cubic ice VII and ice X. We find that thermal
equilibration of the confined water is hindered at high
pressures. We simulate
sliding of the square ice on atomically at graphite and find
extremely low friction due to structural superlubricity. The
conditions needed for this equilibration correspond to low
sliding speeds, and we suggest that the ice observed in
experiments of friction on wet graphite [3, 4] is of this type.
[1] C. Donnet and A. Erdemir, Tribol. Lett. 17, 389 (2004).
[2] A. S. de Wijn, A. Fasolino, A. E. Filippov, and M.
Urbakh, Europhysics Lett. 95, 66002 (2011).
[3] K. B. Jinesh and J. W. M. Frenken, Phys. Rev. Lett. 96,
166103 (2006).
[4] K. B. Jinesh and J. W. M. Frenken, Phys. Rev. Lett. 101,
036101 (2008).
