Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Gecko Foot Adhesive Gets Stronger, Directional Gripping

13.10.2008
The race for the best “gecko foot” dry adhesive got a new competitor this week with a stronger and more practical material reported in the journal Science by a team of researchers from four U.S. institutions.

Scientists have long been interested in the ability of gecko lizards to scurry up walls and cling to ceilings by their toes. The creatures owe this amazing ability to microscopic branched elastic hairs in their toes that take advantage of atomic-scale attractive forces to grip surfaces and support surprisingly heavy loads. Several research groups have attempted to mimic those hairs with structures made of polymers or carbon nanotubes.

In a paper to be published in the October 10 issue of Science, researchers from the University of Dayton, the Georgia Institute of Technology, the Air Force Research Laboratory and the University of Akron describe an improved carbon nanotube-based material that for the first time creates directionally-varied (anisotropic) adhesive force. With a gripping ability nearly three times the previous record – and ten times better than a real gecko at resisting perpendicular shear forces – the new carbon nanotube array could give artificial gecko feet the ability to tightly grip vertical surfaces while being easily lifted off when desired.

Beyond the ability to walk on walls, the material could have many technological applications, including connecting electronic devices and substituting for conventional adhesives in the dry vacuum of space. The research has been sponsored by the National Science Foundation and the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base near Dayton, Ohio.

“The resistance to shear force keeps the nanotube adhesive attached very strongly to the vertical surface, but you can still remove it from the surface by pulling away from the surface in a normal direction,” explained Liming Dai, the Wright Brothers Institute Endowed Chair in the School of Engineering at the University of Dayton. “This directional difference in the adhesion force is a significant improvement that could help make this material useful as a transient adhesive.”

The key to the new material is the use of rationally-designed multi-walled carbon nanotubes formed into arrays with “curly entangled tops,” said Zhong Lin Wang, a Regents’ Professor in the Georgia Tech School of Materials Science and Engineering. The tops, which Wang compared to spaghetti or a jungle of vines, mimic the hierarchical structure of real gecko feet, which include branching hairs of different diameters.

When pressed onto a vertical surface, the tangled portion of the nanotubes becomes aligned in contact with the surface. That dramatically increases the amount of contact between the nanotubes and the surface, maximizing the van der Waals forces that occur at the atomic scale. When lifted off the surface in a direction parallel to the main body of the nanotubes, only the tips remain in contact, minimizing the attraction forces, Wang explained.

“The contact surface area matters a lot,” he noted. “When you have line contact along, you have van der Waals forces acting along the entire length of the nanotubes, but when you have a point contact, the van der Waals forces act only at the tip of the nanotubes. That allows us to truly mimic what the gecko does naturally.”

In tests done on a variety of surfaces – including glass, a polymer sheet, Teflon and even rough sandpaper – the researchers measured adhesive forces of up 100 Newtons per square centimeter in the shear direction. In the normal direction, the adhesive forces were 10 Newtons per square centimeter – about the same as a real gecko.

The resistance to shear increased with the length of the nanotubes, while the resistance to normal force was independent of tube length.

Though the material might seem most appropriate for use by Spider-Man, the real applications may be less glamorous. Because carbon nanotubes conduct heat and electrical current, the dry adhesive arrays could be used to connect electronic devices.

“Thermal management is a real problem today in electronics, and if you could use a nanotube dry adhesive, you could simply apply the devices and allow van der Waals forces to hold them together,” Wang noted. “That would eliminate the heat required for soldering.”

Another application might be for adhesives that work long-term in space. “In space, there is a vacuum and traditional kinds of adhesives dry out,” Dai noted. “But nanotube dry adhesives would not be bothered by the space environment.”

In addition those already mentioned, the research team also included Liangti Qu from the University of Dayton, Morley Stone from the Air Force Research Laboratory, and Zhenhai Xia from the University of Akron.

Qu, a research assistant in the laboratory of Liming Dai, grew the nanotube arrays with a low-pressure chemical vapor deposition process on a silicon wafer. During the pyrolytic growth of the vertically-aligned multi-walled nanotubes, the initial segments grew in random directions and formed a top layer of coiled and entangled nanotubes. This layer helped to increase the nanotube area available for contacting a surface.

Qu noted that sample purity was another key factor in ensuring strong adhesion for the carbon nanotube dry adhesive.

For the future, the researchers hope to learn more about the surface interactions so they can further increase the adhesive force. They also want to study the long-term durability of the adhesive, which in a small number of tests became stronger with each attachment.

And they may also determine how much adhesive might be necessary to support a human wearing tights and red mask.

“Because the surfaces may not be uniform, the adhesive force produced by a larger patch may not increase linearly with the size,” Dai said. “There is much we still need to learn about the contact between nanotubes and different surfaces.”

Technical Contacts: Zhong Lin Wang (404-894-8008); E-mail: (zhong.wang@mse.gatech.edu) or Liming Dai (937-229-2670); E-mail: (liming.dai@notes.udayton.edu).

John Toon | Newswise Science News
Further information:
http://www.gatech.edu

More articles from Physics and Astronomy:

nachricht Unconventional superconductor may be used to create quantum computers of the future
19.02.2018 | Chalmers University of Technology

nachricht Hubble sees Neptune's mysterious shrinking storm
16.02.2018 | 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: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Japanese researchers develop ultrathin, highly elastic skin display

19.02.2018 | Information Technology

Dispersal of Fish Eggs by Water Birds – Just a Myth?

19.02.2018 | Ecology, The Environment and Conservation

Studying mitosis' structure to understand the inside of cancer cells

19.02.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>