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 When fluid flows almost as fast as light -- with quantum rotation
22.06.2018 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

nachricht Thermal Radiation from Tiny Particles
22.06.2018 | Universität Greifswald

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: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>