Models present new view of nanoscale friction

February 25, 2009 by Liz Ahlberg
This graphic recreates an atom-level view of the nanoscale interface between carbon and diamond. At such a small scale, the surfaces are rough, although researchers have been treating them as smooth. Image: Izabela Szlufarska

(PhysOrg.com) -- To understand friction on a very small scale, a team of University of Wisconsin-Madison engineers had to think big.

Friction is a force that affects any application where moving parts come into contact; the more surface contact there is, the stronger the force. At the nanoscale — mere billionths of a meter — friction can wreak havoc on tiny devices made from only a small number of atoms or molecules. With their high surface-to-volume ratio, nanomaterials are especially susceptible to the forces of friction.

But researchers have trouble describing friction at such small scales because existing theories are not consistent with how nanomaterials actually behave. Through computer simulations, the group demonstrated that friction at the atomic level behaves similarly to friction generated between large objects. Five hundred years after Leonardo da Vinci discovered the basic friction laws for large objects, the UW-Madison team has shown that similar laws apply at the nanoscale.

The team, which was led by Izabela Szlufarska, an assistant professor of materials science and engineering, and included materials science and engineering graduate student Yifei Mo and mechanical engineering assistant professor Kevin Turner, published its findings in the Feb. 26 issue of the journal Nature.

Current nanoscale friction theories are based on the idea that nanoscale surfaces are smooth, but, in reality, the surfaces resemble a mountain range, where each peak corresponds to an atom or a molecule.

The UW-Madison team performed computer simulations that looked at nanoscale materials as a collection of atoms, monitoring their positions and interactions throughout the entire sliding process. "For the first time, we modeled friction at length scales very similar to experiments, while maintaining atomic resolution and realistic interactions between atoms," say Szlufarska.

The team discovered simple laws of nanoscale friction. They found that friction is proportional to the number of atoms that interact between two nanoscale surfaces. The researchers' simulations showed that, at the nanoscale, materials in contact behave more like large rough objects rubbing against each other, rather than as two perfectly smooth surfaces, as was previously imagined. "When you look at it closely, the surface is made of atoms, so the contact is actually rough," says Szlufarska.

The team's simulation data correlates very well with recorded experimental data — something that previous models have failed to accomplish. Szlufarska hopes to use the simulations as a tool to understand what mechanisms contribute to friction on both the nano- and macroscale.

"Nobody is able to predict friction or design materials with desired friction properties — we measure a lot of friction coefficients for different materials, but it's not really clear how to relate them to the properties of the material," she explains. "The origin of friction is really an open and growing research
field."

Provided by University of Wisconsin-Madison

Explore further: Is graphene hydrophobic or hydrophilic?

Related Stories

Is graphene hydrophobic or hydrophilic?

August 18, 2015

The National Physical Laboratory's (NPL) Quantum Detection Group has just published research investigating the hydrophobicity of epitaxial graphene, which could be used in the future to better tailor graphene coatings to ...

Rice, Penn State open center for 2-D coatings

August 13, 2015

A new center at Rice University and Pennsylvania State University will study, in collaboration with industry, the development of atom-thin two-dimensional coatings for a variety of uses.

Simulations lead to design of near-frictionless material

July 22, 2015

Argonne scientists used Mira to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. Argonne ...

Varying the sliding properties of atoms on a surface

June 22, 2015

It's possible to vary (even dramatically) the sliding properties of atoms on a surface by changing the size and "compression" of their aggregates: an experimental and theoretical study conducted with the collaboration of ...

Recommended for you

Electrical circuit made of gel can repair itself

August 25, 2015

(Phys.org)—Scientists have fabricated a flexible electrical circuit that, when cut into two pieces, can repair itself and fully restore its original conductivity. The circuit is made of a new gel that possesses a combination ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

superhuman
not rated yet Feb 26, 2009
The researchers simulations showed that, at the nanoscale, materials in contact behave more like large rough objects rubbing against each other, rather than as two perfectly smooth surfaces, as was previously imagined


This is typical for the pathetic science reporting here. To make the discoveries more exciting the articles purposefully misrepresent the state of prior knowledge.

No one, expect perhaps for science illiterates, imagined object surfaces are smooth at nano scale!

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.