A team of researchers in the Faculty of Engineering at the University of Alberta are developing new adhesives inspired by gecko’s feet that have directional stickiness. Think of Spiderman climbing up the side of a building and you’ve got the picture!
Mechanical engineering professor Dan Sameoto and his research team have recently published results of their research in which they turn flaws in previous experiments into a huge advantage. The result is an adhesive strip that sticks more when pulled in one direction than in another. It’s effectively tape that sticks to a surface strongly when pushed in one direction and slips off when you push it in the opposite direction.
Sameoto and graduate student Walid Bin Khaled are conducting research in a field of adhesives inspired by gecko’s feet. The bottoms of tiny lizard’s feet are covered with millions of tiny hairs with a triangular shaped end that allow it to climb up walls and across ceilings. Like a gecko’s feet, the adhesives Sameoto has been researching for years have tiny stalks, like hairs, that connect time and time again with a variety of surfaces without leaving residue. In recent years, researchers have discovered that by adjusting the stalks so that they have an overhanging cap tip, can in turn increase the material’s adhesive strength.
When there are defects on these caps, the bond is broken more easily.
Sameoto and Khaled cleverly realized that if they intentionally introduced defects in the same place on each of the caps of all the stalks, they could turn the “defect” into an advantage and create a directional adhesion.
“We noticed that every time there was a defect in a cap, or a tiny speck of dust or anything on it, that was the site at which the adhesion would fail,” said Sameoto. “Then we thought ‘Maybe we can control this.’”
Peeling a strip of the adhesive off of a glass surface in one direction then another, Sameoto observes that “you can even hear the difference,” as the strip releases differently in opposite directions.
Applications for dry adhesives are far-reaching. For example, in the production of microelectronics, tiny chips are handled in high-tech clean rooms by workers who wear ‘bunny suits’ and use tweezers to handle the chips. But robotics could get the same job done in a vacuumed environment instead of a clean room, using the dry adhesive instead of tweezers. The adhesive could also replace suction cups used in other applications – including work in outer space.
“Our adhesives can potentially be used in all these applications because it demonstrated reasonably strong normal adhesion strength with respect to the adhesives which were used for these systems,” said Khaled.
The team is also looking for ways to eliminate the build-up of static charge in the strips that occurs with some materials.
“It is less severe with the thermoplastic adhesives as compared to the pure polyurethane ones,” said Khaled. “We actually made a version of these adhesives using a polyurethane-carbon black nano-composite which is conductive and does not allow static build up, and we are currently exploring some new thermoplastic materials which would be conductive or at least antistatic.”
This article was published on October 31, 2013, in the University of Alberta’s Faculty of Engineering webpage.