Fullerene spheres can be used to slide in the nanoworld

October 3, 2014

"Nano–machines" (around one billionth of a metre in size) of the future will need tiny devices to reduce friction and make movement possible. The C60 molecule, also known as fullerene or buckyball, seemed to many an excellent candidate for nano-bearings. Unfortunately, the results so far have been conflicting, calling for further studies, like the one carried out by a theoretical team involving SISSA, ICTP, CNR and EMPA. Through a series of computer simulations the scientists uncovered the reason for the experimental discrepancies and shed light on the true potential of this material.

About 3500 years ago, man invented the wheel to make life easier. Then, thanks to Leonardo Da Vinci's genius, the wheel was made smaller to obtain . And today? "Today we are trying to get even smaller: scientists are thinking about nano-bearings", comments Andrea Vanossi, of the CNR – Democritos and the International School for Advanced Studies (SISSA) of Trieste, among the authors of a study that has just been published in Nanoscale. "In the future we'll have many nano-machines capable of carrying out the most diverse tasks, for example transporting medicines inside the human body. In order to save energy, many of these vehicles will have to able to move efficiently, using as little energy as possible, and "nano"-sized ball bearings may help achieve this goal".

"Scientists thought they could use C60, a hollow carbon nanosphere, measuring one nanometre in diameter", explains Erio Tosatti, SISSA professor and another author of the study", but there's a problem: the experimental results are at complete variance with each other". C60 has a temperature (260° Kelvin) at which the molecules suddenly become free to rotate, which hopefully has a role in . The two most important experiments carried out to date, however, have yielded conflicting results: above this temperature, when the material was made to slide over a substrate, in one case there was no significant decrease in friction, whereas in the other the decrease was dramatic, a good 100%. "What's going on? If we assume that the measurements are correct and the experiments performed correctly (and we have no reason to believe otherwise) how do we explain this difference?", wonders Vanossi. "For this reason, we decided to verify".

The team (a collaboration between SISSA, the International Centre for Theoretical Physics "Abdus Salam" ICTP of Trieste, the Italian National Research Council CNR, and the Swiss Federal Laboratories for Materials Science and Technology) conducted a theoretical, simulation-based study.

"We simulated the tiny tip of an electron microscope bearing a C60 flake, which was dragged over a surface also made of C60", explains Vanossi. "We discovered that when the flake was attached in such a way that it couldn't rotate the friction did not decrease, even if we raised the temperature to above 260° K. It's as if the bearings making up the flake interlocked with the substrate, with no nano-bearing effect. However, when the flake was free to rotate there was a dramatic drop in friction and the flake could slide over the surface far more smoothly".  But here the drop in friction is not due to the ball bearing effect, but to the change in contact geometry.

The two states therefore reproduce the results of the two experiments. "Our data faithfully reflect the empirical observations", concludes Tosatti. "This of course does not bode well for the future use of fullerite to reduce friction at the nanoscale, in that the nanobearing function is not confirmed, but it does finally shed light on the physics of this problem".

The video compares the two sliding states of the C60 flake attached to the tip of the microscope: a) commensurate state at low temperature where the C60 do not rotate and the system shows stick-slip (high) friction and b) incommensurate state at high temperature where the C60 rotate and the flake moves more smoothly (low friction). The green points simply colour one of the 60 atoms making up the C60 molecules to better highlight the absence/presence of rotation below/above the critical temperature. Credit: SISSA

Explore further: How do cold ions slide

More information: Does rotational melting make molecular crystal surfaces more slippery? Andrea Benassi, Andrea Vanossi,Carlo A. Pignedoli,Daniele Passeroneand Erio Tosatti Nanoscale, 2014, Advance Article DOI: 10.1039/C4NR04641B

Related Stories

How do cold ions slide

May 23, 2013

Things not always run smoothly. It may happen, actually, that when an object slides on another, the advancement may occur through a 'stop and go' series in the characteristic manner which scientists call "stick-slip", a pervasive ...

Molecules as circuits

January 23, 2014

Pursuit of silicon-based electronics has certain limits, in the physical sense: This type of circuit can never become "nano" because of the physical laws governing the flow of electrons. This imposes a halt to the process ...

The quantum dance of oxygen

July 7, 2014

Under extremely high pressure conditions oxygen molecules group into quartets and give rise to a 'dance of their magnetic moments.' This, as observed in a new study carried out by SISSA in collaboration with ICTP and published ...

The ferromagnetic Kondo effect

July 24, 2013

A group of physicists that includes scientists of the International School for Advanced Studies (SISSA) of Trieste have shown how to obtain a particular case of a physical effect – so far never observed in reality – whose ...

Recommended for you

Borophene shines alone as 2-D plasmonic material

November 20, 2017

An atom-thick film of boron could be the first pure two-dimensional material able to emit visible and near-infrared light by activating its plasmons, according to Rice University scientists.

Clothing fabric keeps you cool in the heat

November 16, 2017

(Phys.org)—Researchers have designed a thermal regulation textile that has a 55% greater cooling effect than cotton, which translates to cooler skin temperatures when wearing clothes made of the new fabric. The material ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 03, 2014
Nice work!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.