Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Size matters: Friction, adhesion change on atomic level

30.06.2005


Physicists have a pretty good idea of what to expect when friction and adhesion occur in the visible world. You jam on the brakes, for instance, and your tires and the highway interact to stop your car. You glue two pieces of wood together, and they stick.
But how slippery or sticky are things that are too small to see? When solid surfaces no more than a thousand atoms across brush past each other, will they respond like the rubber and the road? Will they adhere like the wood and the glue?

The answer turns out to be "It depends," according to Johns Hopkins physicists who used computer modeling to examine how friction and adhesion operate on the atomic level.


"Any surface made of individual atoms has ’bumps’ of atomic dimension, and being able to vary the placement of atoms [in the computer models] allowed us to quantify the influence of atomic structure," said Mark O. Robbins, a professor in the Henry A. Rowland Department of Physics and Astronomy in the university’s Krieger School of Arts and Sciences.

The modeling showed that surfaces from a few to a thousand atoms across, with the same shape, but with different local structures, or "bumps," behave quite differently, even if those surfaces are made of the same material, Robbins said. Local stresses and adhesion forces can vary by a factor of two or more, and friction can change tenfold, he said.

The research is reported in the June 16 issue of the journal Nature by Robbins and graduate student Binquan Luan. Their findings could one day help in the successful design of nanomachines, the name given to devices built by manipulating materials on an atomic scale. "Everyone knows that matter is made up of discrete atoms, yet most models of mechanical behavior ignore this and think of atoms as being ’smeared’ into an artificial continuous medium," Robbins said. "This approach works well when describing the behavior of larger machines, but what happens when the whole machine is only a few to a thousand atoms across? The answer is crucial to the function of man-made nanomachines and many biological processes."

Robbins’ and Luan examined contact between solid surfaces with "bumps" whose radii varied from about 100 to 1,000 atomic diameters. Bumps that size might be typical of nanomachine surfaces or the tips of atomic force microscopes used to measure mechanical properties at the atomic scale.

Using computer simulations, the team followed the displacements of up to 10 million atoms as the solid surfaces were pushed together. They then compared these displacements and the total adhesion and friction forces to calculations of the same forces using the standard "continuum theory," the model that views matter as having smeared rather than discrete atoms.

"Knowing the exact atomic structure and how each atom moved allowed us to test the two key assumptions of continuum theory," Robbins said. "While it described the internal response of solids down to nearly atomic scales, its assumption that surfaces are smooth and featureless failed badly" at the atomic level.

In a "News and Views" paper accompanying the Nature article, Jacob Israelachvili of University of California, Santa Barbara, noted that these results have fundamental implications for the limits of theories that try to "smear out" atomic structure, as well as indicating "how surfaces might be tailored in desirable ways ... if atomic-scale details are taken into consideration." This work is important because of the growing interest in nanotechnology, in which unwanted adhesion and excessive friction can cause devices to malfunction or just not to work, Robbins said. "Hopefully, this will help in the creation of new tools needed to guide the design of nanotechnology" he said.

Lisa DeNike | EurekAlert!
Further information:
http://www.jhu.edu

More articles from Physics and Astronomy:

nachricht Taking a spin on plasma space tornadoes with NASA observations
20.11.2017 | NASA/Goddard Space Flight Center

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Antarctic landscape insights keep ice loss forecasts on the radar

20.11.2017 | Earth Sciences

Filling the gap: High-latitude volcanic eruptions also have global impact

20.11.2017 | Earth Sciences

Water world

20.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>