MATERIALS SCIENCE
Buckyball additives improve lubrication
Molecules shaped like spheres conjure up images of microscopic ball bearings that can
reduce friction between tiny moving components.
When researchers discovered the buckminsterfullerene molecule in 1985, they thought they
had found the ideal candidate for such a role. Consisting of 60 carbon atoms, this molecule is
a nearly perfect sphere. In the crystalline solid state, it spins at a rate dependent on temperature,
while remaining in its position in the crystal lattice.
Those hopes were dashed when subsequent experiments demonstrated that buckyballs are
not particularly good lubricants. Now, a team of chemical engineers and chemists has discovered
that C60 molecules dissolved in the organic solvent toluene greatly reduce the friction
between the liquid and the surface across which it flows.
This finding suggests that the addition of buckyballs to conventional lubricating fluids may
enhance their performance. Jacob N. Israelachvili, Fred Wudl, and their coworkers at the
University of California, Santa Barbara report their results in the Aug. 8 NATURE.
The researchers measured oscillating, attractive forces between a pair of smooth, transparent
sheets of mica immersed in toluene as the distance between the surfaces was varied. When
the liquid contained small quantities of C60 molecules, the forces between the mica plates
changed in a manner suggesting that thin layers of buckminsterfullerene molecules had settled
on the mica surfaces. The molecular spheres allowed the liquid to pass easily between the
mica sheets, “giving rise to flow behavior that is totally different from conventional fluid flow
through narrow pores,” the researchers note.
A possible explanation of this result is that the adsorbed layer of molecules is only weakly
bound to the surface and, as in the crystalline solid, the buckyballs may be rotating rapidly,
allowing toluene molecules to slide by easily.
In contrast, measurements of the forces between a pair of solid layers of C60 in the absence
of a liquid confirm that the molecules by themselves offer no significant reduction in friction.
“The results . . . indicate that C60, although not a good lubricant, shows great promise as an
additive,” Israelachvili and his colleagues conclude.
August 31, 1996
Vol. 150 No. 9 p. 139
Copyright ©1996 by Science Service |
買百達的油精加也不錯~
