Nav: Home

Nanotube 'rebar' makes graphene twice as tough

August 03, 2018

HOUSTON - (Aug. 3, 2018) - Rice University researchers have found that fracture-resistant "rebar graphene" is more than twice as tough as pristine graphene.

Graphene is a one-atom-thick sheet of carbon. On the two-dimensional scale, the material is stronger than steel, but because graphene is so thin, it is still subject to ripping and tearing.

Rebar graphene is the nanoscale analog of rebar (reinforcement bars) in concrete, in which embedded steel bars enhance the material's strength and durability. Rebar graphene, developed by the Rice lab of chemist James Tour in 2014, uses carbon nanotubes for reinforcement.

In a new study in the American Chemical Society journal ACS Nano, Rice materials scientist Jun Lou, graduate student and lead author Emily Hacopian and collaborators, including Tour, stress-tested rebar graphene and found that nanotube rebar diverted and bridged cracks that would otherwise propagate in unreinforced graphene.

The experiments showed that nanotubes help graphene stay stretchy and also reduce the effects of cracks. That could be useful not only for flexible electronics but also electrically active wearables or other devices where stress tolerance, flexibility, transparency and mechanical stability are desired, Lou said.

Both the lab's mechanical tests and molecular dynamics simulations by collaborators at Brown University revealed the material's toughness.

Graphene's excellent conductivity makes it a strong candidate for devices, but its brittle nature is a downside, Lou said. His lab reported two years ago that graphene is only as strong as its weakest link. Those tests showed the strength of pristine graphene to be "substantially lower" than its reported intrinsic strength. In a later study, the lab found molybdenum diselenide, another two-dimensional material of interest to researchers, is also brittle.

Tour approached Lou and his group to carry out similar tests on rebar graphene, made by spin-coating single-walled nanotubes onto a copper substrate and growing graphene atop them via chemical vapor deposition.

To stress-test rebar graphene, Hacopian, Yang and colleagues had to pull it to pieces and measure the force that was applied. Through trial and error, the lab developed a way to cut microscopic pieces of the material and mount it on a testbed for use with scanning electron and transmission electron microscopes.

"We couldn't use glue, so we had to understand the intermolecular forces between the material and our testing devices," Hacopian said. "With materials this fragile, it's really difficult."

Rebar didn't keep graphene from ultimate failure, but the nanotubes slowed the process by forcing cracks to zig and zag as they propagated. When the force was too weak to completely break the graphene, nanotubes effectively bridged cracks and in some cases preserved the material's conductivity.

In earlier tests, Lou's lab showed graphene has a native fracture toughness of 4 megapascals. In contrast, rebar graphene has an average toughness of 10.7 megapascals, he said.

Simulations by study co-author Huajian Gao and his team at Brown confirmed results from the physical experiments. Gao's team found the same effects in simulations with orderly rows of rebar in graphene as those measured in the physical samples with rebar pointing every which way.

"The simulations are important because they let us see the process on a time scale that isn't available to us with microscopy techniques, which only give us snapshots," Lou said. "The Brown team really helped us understand what's happening behind the numbers."

He said the rebar graphene results are a first step toward the characterization of many new materials. "We hope this opens a direction people can pursue to engineer 2D material features for applications," Lou said.
Hacopian, Yingchao Yang of the University of Maine and Bo Ni of Brown University are co-lead authors of the paper. Co-authors are Yilun Li, Hua Guo of Rice, Xing Li of Rice and Zhengzhou University and Qing Chen of Peking University. Lou is a professor of materials science and nanoengineering at Rice. Tour is the T.T. and W.F. Chao Chair in Chemistry and a professor of computer science and of materials science and nanoengineering Rice. Gao is the Walter H. Annenberg Professor of Engineering at Brown.

The research was supported by the Welch Foundation, the Air Force Office of Scientific Research's Multidisciplinary University Research Institute, the Department of Energy Office of Basic Energy Sciences, the National Natural Science Foundation of China and the National Science Foundation.

Read the abstract at

This news release can be found online at

Follow Rice News and Media Relations via Twitter @RiceUNews Video:

Simulations show how carbon nanotubes can make graphene twice as tough by acting as reinforcement bars, like steel in concrete. Scientists at Brown University worked with experimentalists at Rice University to show how rebar helps bridge or redirect cracks in graphene under strain. (Video courtesy of the Gao Research Group/Brown University)

Images for download:

An image depicts a sample of rebar graphene after testing under an electron microscope by materials scientists at Rice University. It shows how cracks propagate in a zigzag way, rather than straight, as would be seen in plain graphene. The rebar graphene is attached by molecular forces on both sides to a platform that slowly pulls the material apart. (Credit: Emily Hacopian/Rice University)

Rice University graduate student Emily Hacopian holds the platform she used to study the strength of rebar graphene under a microscope. Hacopian and colleagues discovered that reinforcing graphene with carbon nanotubes makes the material twice as tough. (Credit: Jeff Fitlow/Rice University)

Rice University graduate student Emily Hacopian and materials scientist Jun Lou led a team that tested the toughness of rebar graphene. (Credit: Jeff Fitlow/Rice University)

Related materials:

Rebar strengthens case for graphene:

Lou Group:

Tour Group:

Gao Research Group:

Yang Group:

Rice Department of Materials Science and NanoEngineering:

Rice Department of Chemistry:

George R. Brown School of Engineering:

Wiess School of Natural Sciences:

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,970 undergraduates and 2,934 graduate students, Rice's undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for quality of life and for lots of race/class interaction and No. 2 for happiest students by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to

Rice University

Related Graphene Articles:

New chemical method could revolutionize graphene
University of Illinois at Chicago scientists have discovered a new chemical method that enables graphene to be incorporated into a wide range of applications while maintaining its ultra-fast electronics.
Searching beyond graphene for new wonder materials
Graphene, the two-dimensional, ultra lightweight and super-strong carbon film, has been hailed as a wonder material since its discovery in 2004.
New method of characterizing graphene
Scientists have developed a new method of characterizing graphene's properties without applying disruptive electrical contacts, allowing them to investigate both the resistance and quantum capacitance of graphene and other two-dimensional materials.
Chemically tailored graphene
Graphene is considered as one of the most promising new materials.
Beyond graphene: Advances make reduced graphene oxide electronics feasible
Researchers have developed a technique for converting positively charged (p-type) reduced graphene oxide (rGO) into negatively charged (n-type) rGO, creating a layered material that can be used to develop rGO-based transistors for use in electronic devices.
The Graphene 2017 Conference connects Barcelona with the international graphene-based industry
This prestigious Conference to be held at the Barcelona International Convention Centre (March 28-31) aims to bring together academia and industry to integrate new graphene technologies into practical applications.
Graphene from soybeans
A breakthrough by CSIRO-led scientists has made the world's strongest material more commercially viable, thanks to the humble soybean.
First use of graphene to detect cancer cells
By interfacing brain cells onto graphene, researchers at the University of Illinois at Chicago have shown they can differentiate a single hyperactive cancerous cell from a normal cell, pointing the way to developing a simple, noninvasive tool for early cancer diagnosis.
Development of graphene microwave photodetector
DGIST developed cryogenic microwave photodetector which is able to detect 100,000 times smaller light energy compared to the existing photedetectors.
Adding hydrogen to graphene
IBS researchers report a fundamental study of how graphene is hydrogenated.

Related Graphene Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...