Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > Penn Engineers Advance Understanding of Graphene’s Friction Properties

A comparison between the energy corrugation of graphene (above) and fluorinated graphene (below).
A comparison between the energy corrugation of graphene (above) and fluorinated graphene (below).

Abstract:
An interdisciplinary team of engineers from the University of Pennsylvania has made a discovery regarding the surface properties of graphene, the Nobel-prize winning material that consists of an atomically thin sheet of carbon atoms.

Penn Engineers Advance Understanding of Graphene’s Friction Properties

Philadelphia, PA | Posted on September 10th, 2014

On the macroscale, adding fluorine atoms to carbon-based materials makes for water-repellant, non-stick surfaces, such as Teflon. However, on the nanoscale, adding fluorine to graphene had been reported to vastly increase the friction experienced when sliding against the material.

Through a combination of physical experiments and atomistic simulations, the Penn team has discovered the mechanism behind this surprising finding, which could help researchers better design and control the surface properties of new materials.

The research was led by postdoctoral researcher Qunyang Li, graduate student Xin-Zhou Liu and Robert Carpick, professor and chair of the Department of Mechanical Engineering and Applied Mechanics in Penn's School of Engineering and Applied Science. They collaborated with Vivek Shenoy, a professor in the Department of Materials Science and Engineering. The Penn contingent also worked with researchers from the Naval Research Laboratory and Brown University.

The work was published in Nano Letters.

Besides its applications in circuitry and sensors, graphene is of interest as a super-strong coating. As components of mechanical and electrical systems get smaller, they are increasingly susceptible to wear and tear. Made up of fewer atoms than their macroscale counterparts, each atom is that much more important to the component's overall structure and function.

"One of the major failure mechanisms for these small-scale devices is friction and adhesion," Liu said. "Because graphene is so strong, thin and smooth, one of its potential applications is to reduce friction and increase the lifespan of these devices. We wanted to better understand the fundamental mechanisms of how the addition of other atoms influences the friction of graphene."

The addition of fluorine atoms to graphene's carbon lattice makes for an intriguing combination when it comes to those properties.

"Generally speaking," Carpick said, "fluorine makes surfaces more water-repellent and non-stick. Gore-Tex and Teflon, for example, get their properties from fluorine. Teflon is a fluorinated carbon polymer, so we thought fluorinated graphene might be like two-dimensional Teflon."

To test the friction properties of this material, the Penn researchers collaborated with Paul Sheehan and Jeremy Robinson of the Naval Research Laboratory. Sheehan and Robinson were the first to discover fluorinated graphene and are experts in producing samples of the material to specification.

"This meant we were able to systematically vary the degree of fluorination in our graphene samples and quantify it precisely," Liu said. "That let us make accurate comparisons when we tested the friction of these different samples with an atomic force microscope, an ultra-sensitive instrument that can measure nanonewton forces."

The researchers were surprised to find that adding fluorine to graphene increased the material's friction but could not immediately explain the mechanism responsible. Another group of researchers had simultaneously made the same observation; they also showed that the addition of fluorine increased the stiffness of the graphene samples and hypothesized this was responsible for the increased friction.

The Penn researchers, however, thought another mechanism must be at work. They turned to Shenoy, whose expertise is in developing atomic scale simulations of mechanical action, to help explain what the addition of the fluorine was doing to the graphene's surface.

"We don't have a microscope that can visualize what's happening at this small scale," Shenoy said, "but there are few enough atoms that we can model how they behave with a high degree of accuracy."

"It turns out that by adding fluorine," Liu said, "we're changing the energy corrugation landscape of the graphene. We're essentially introducing electronic roughness, which at the nanoscale, can act like physical roughness in increasing friction."

In fluorinated graphene, the fluorine atoms do stick up out of the plane of carbon atoms, but the physical changes in height paled in comparison to the changes of local energy each fluorine atom produced.

"At the nanoscale," Carpick said, "friction isn't just determined by the placement of atoms but also how much energy is in their bonds. Each fluorine atom has so much electronic charge that you get tall peaks and deep valleys in between them, compared to the smooth plane of regular graphene. You could say it's like trying slide over a smooth road versus a bumpy road."

Beyond the implication for graphene's coating applications, the team's findings provide fundamental insight into graphene's surface properties.

"Every material interacts with the world through its surface," Carpick said, "so understanding and manipulating surface properties — friction, adhesion, interactions with water, catalysis — are major, ongoing areas of scientific research. Seeing that fluorine increases friction in graphene isn't necessarily a bad thing, since it may give us a way to tailor that property to a given application. It also will help us understand how the addition of other elements, like hydrogen or oxygen, might influence those properties."

The research was supported by the National Science Foundation, Korea Institute of Machinery and Materials and Office of Naval Research.

####

For more information, please click here

Contacts:
Evan Lerner

215-573-6604

Copyright © University of Pennsylvania

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Download article:

Related News Press

News and information

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Graphene/ Graphite

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Govt.-Legislation/Regulation/Funding/Policy

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Institute for Nanoscience hosts annual proposal planning meeting May 16th, 2025

Rice researchers harness gravity to create low-cost device for rapid cell analysis February 28th, 2025

Discoveries

Researchers unveil a groundbreaking clay-based solution to capture carbon dioxide and combat climate change June 6th, 2025

Cambridge chemists discover simple way to build bigger molecules – one carbon at a time June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Materials/Metamaterials/Magnetoresistance

Researchers unveil a groundbreaking clay-based solution to capture carbon dioxide and combat climate change June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Institute for Nanoscience hosts annual proposal planning meeting May 16th, 2025

Superconductors: Amazingly orderly disorder: A surprising effect was discovered through a collaborative effort by researchers from TU Wien and institutions in Croatia, France, Poland, Singapore, Switzerland, and the US during the investigation of a special material: the atoms are May 14th, 2025

Announcements

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters

Cambridge chemists discover simple way to build bigger molecules – one carbon at a time June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Military

Quantum engineers ‘squeeze’ laser frequency combs to make more sensitive gas sensors January 17th, 2025

Chainmail-like material could be the future of armor: First 2D mechanically interlocked polymer exhibits exceptional flexibility and strength January 17th, 2025

Single atoms show their true color July 5th, 2024

NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project