Nanotube Adhesive Sticks Better Than a Gecko’s Foot

[C1ay]

Mimicking the agile gecko, with its uncanny ability to run up walls and across ceilings, has long been a goal of materials scientists. Researchers at Rensselaer Polytechnic Institute and the University of Akron have taken one sticky step in the right direction, creating synthetic “gecko tape” with four times the sticking power of the real thing.

 

lefthttp://hypography.com/gallery/files/9/9/8/geckodiag_thumb.jpg[/img]In a paper published in the June 18–22 issue of the Proceedings of the National Academy of Sciences, the researchers describe a process for making polymer surfaces covered with carbon nanotube hairs. The nanotubes imitate the thousands of microscopic hairs on a gecko’s footpad, which form weak bonds with whatever surface the creature touches, allowing it to “unstick” itself simply by shifting its foot.

 

For the first time, the team has developed a prototype flexible patch that can stick and unstick repeatedly with properties better than the natural gecko foot. They fashioned their material into an adhesive tape that can be used on a wide variety of surfaces, including Teflon.

 

Pulickel Ajayan, the Henry Burlage Professor of Materials Science and Engineering at Rensselaer, and Lijie Ci, a postdoctoral research associate in Ajayan’s lab, created the material in collaboration with Ali Dhinojwala, professor of polymer science at the University of Akron, and University of Akron graduate students Liehui Ge and Sunny Sethi.

 

“Several people have tried to use carbon nanotube films and other fibrous structures as high-adhesive surfaces and to mimic gecko feet, but with limited success when it comes to realistic demonstrations of the stickiness and reversibility that one sees in gecko feet,” Ajayan said. “We have shown that the patchy structures from micropatterned nanotubes are essential for this unique engineering feat to work. The nanotubes also need to be the right kind, with the right dimensions and compliance.”

 

“Geckos inspired us to develop a synthetic gecko tape unlike any you’ll find in a hardware store,” Dhinojwala says. “Synthetic gecko tape uses ‘van der Waals interactions’ — the same interactions that hold liquids and solids together — to stick to a variety of surfaces without using sticky glues.”

 

The material could have a number of applications, including feet for wall-climbing robots; a dry, reversible adhesive in electronic devices; and outer space, where most adhesives don’t work because of the vacuum.

 

The research was funded by the National Science Foundation.

 

Source: Rensselaer Polytechnic Institute

[InfiniteNow]

That's rather cool.

 

Synthetic gecko tape uses ‘van der Waals interactions’ — the same interactions that hold liquids and solids together — to stick to a variety of surfaces without using sticky glues.

 

I wonder if it could be used to "tape" together two pieces of ice... Further, I'd be interested to see some studies on it's reaction at different temperatures... like "hot." I imagine they're still too early in the research to know much, but it's very cool all the same. As always, thanks for sharing with the rest of us, C1ay. :confused:

[Jay-qu]

We will be walking up the sides of buildings and hanging from the ceiling in no time :confused:

[freeztar]

Yeah, I want some Gecko shoes!

 

One question, why does tape not work in a vacuum?

[InfiniteNow]

One question, why does tape not work in a vacuum?

From what I've read, it appears that the linkage formed by adhesives is both mechanical and molecular, and that the ability of the tape to stick to the surface is contingent on it's ability to be "pushed" against it. Generally, it is air pressure doing the pushing, and in space this is absent. However, I didn't get much farther than that.

 

Here is a link to the actual article published by the researchers, however it requires paid subscription:

 

Abstract (free) : Carbon nanotube-based synthetic gecko tapes -- Ge et al., 10.1073/pnas.0703505104 -- Proceedings of the National Academy of Sciences

 

Full Text (subscription only): PNAS -- Sign In Page

[freeztar]

From what I've read, it appears that the linkage formed by adhesives is both mechanical and molecular, and that the ability of the tape to stick to the surface is contingent on it's ability to be "pushed" against it. Generally, it is air pressure doing the pushing, and in space this is absent. However, I didn't get much farther than that.

 

Perhaps I'm taking "pushed" too literally, but wouldn't gecko tape need to be pushed onto a surface as well? And would not the nanotubes interacting with the surface be considered molecular?

 

I'm going to hazard a guess and say that in a vacuum, you do not have space between the molecules because of lack of air. Perhaps this air space is critical for the "intertwining" to work.

I'm envisioning something like a peice of velcro made out of minature balloons. With the baloons deflated, no "hooks" would exist to snag each other.

Here is a link to the actual article published by the researchers, however it requires paid subscription:

 

Abstract (free) : Carbon nanotube-based synthetic gecko tapes -- Ge et al., 10.1073/pnas.0703505104 -- Proceedings of the National Academy of Sciences

 

Full Text (subscription only): PNAS -- Sign In Page

 

While I do like reading published journal articles, I can't afford it.

[InfiniteNow]

Perhaps I'm taking "pushed" too literally, but wouldn't gecko tape need to be pushed onto a surface as well? And would not the nanotubes interacting with the surface be considered molecular?

 

I'm going to hazard a guess and say that in a vacuum, you do not have space between the molecules because of lack of air. Perhaps this air space is critical for the "intertwining" to work.

I'm envisioning something like a peice of velcro made out of minature balloons. With the baloons deflated, no "hooks" would exist to snag each other.

It appears you're pretty close.

 

Straight Dope Staff Report: How does glue work?

A good adhesive has excellent properties of adhesion (the ability to stick to the surfaces to which it's applied) and cohesion (the ability to stick to itself). When you pull apart something that's been glued together and the glue comes right off the pieces, that's an adhesive failure. If the glue itself splits apart, leaving glue on either side of the joint, then that's a cohesive failure:

There's no universally accepted theory, and given the variety of adhesives more than one process may be at work. It's generally agreed that adhesion occurs at the molecular level, the chief processes involved being Van der Waals forces, ionic bonding, covalent bonding, and metallic bonding.

According to recent research, Van der Waals forces explain how the lizards known as geckos can stick to so many surfaces in a seemingly impossible manner. Specifically, the tiny hairs on the gecko's feet (called setae) are split at the microscopic level into "as many as 1,000 branches, whose spatula-shaped tips are only 200 nanometers wide." As a result, even though the Van der Waals forces acting on an individual tip is small, the adhesion of a billion or so tips adds up to enough force to let the gecko stick to anything.

 

Persuasive as all this sounds, other scientists doubt that Van der Waals forces alone fully explain how glue works. They attribute at least some of the strength of adhesives to mechanical bonding, also known as mechanical locking. The idea here is that all surfaces, even seemingly smooth ones, are actually rough at the molecular level, and that an adhesive achieves some of its strength by flowing into the hidden valleys and imperfections of the surfaces to be bonded...In mechanical bonding as with Van der Waals forces, an adhesive needs to be able to spread finely into the microscopic roughness of the surfaces, wet the tiny cracks properly, and allow trapped air to escape. The main difference is that mechanical bonding will work at distances that would render Van der Waals forces useless.

Still another type of adhesion involves the presence of tiny air bubbles--in 1999, French researchers presented a theory in Discover magazine that instant adhesives (like that used in Scotch-brand tape and Post-It notes) actually work by creating numerous microscopic bubbles each having a partial vacuum in them, which act as suction cups.

[Jay-qu]

Its an interesting subject, adhesion - I have always found it puzzling, you can look at something and feel it and know that its sticky, but are at a loss to say why its sticky.

 

Anyone interested in starting a thread on this sticky matter at hand?

[InfiniteNow]

Anyone interested in starting a thread on this sticky matter at hand?

Consider it done... It's been posted at the below... I guess you can say that I executed Jay's request to, "Post-it."

 

http://hypography.com/forums/engineering-applied-science/11941-eww-why-so-sticky.html#post178893

 

 

:rant: