la7036907_si_003.pdf (45.63 kB)
Superlubricity Using Repulsive van der Waals Forces
journal contribution
posted on 2008-03-18, 00:00 authored by Adam A. Feiler, Lennart Bergström, Mark W. RutlandUsing colloid probe atomic force microscopy, we show that if repulsive van der Waals forces exist between two
surfaces prior to their contact then friction is essentially precluded and supersliding is achieved. The friction measurements
presented here are of the same order as the lowest ever recorded friction coefficients in liquid, though they are achieved
by a completely different approach. A gold sphere attached to an AFM cantilever is forced to interact with a smooth
Teflon surface (templated on mica). In cyclohexane, a repulsive van der Waals force is observed that diverges at short
separations. The friction coefficient associated with this system is on the order of 0.0003. When the refractive index
of the liquid is changed, the force can be tuned from repulsive to attractive and adhesive. The friction coefficient
increases as the Hamaker constant becomes more positive and the divergent repulsive force, which prevents solid−solid contact, gets switched off.