Penn State Behrend Undergraduate Academic Year Research Grant Program 2009-2010
Self Cleaning “Gecko Tape” October 27, 2009
Penn State Behrend School of Science
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Olivia Rose Derby
5620 East Lake Rd. Apt 3
Erie PA 16511
716.640.8276
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Jesse Gresh
108 Turner Hall
814.881.0353
Abstract
Research into the self cleaning properties of the super adhesive “Gecko Tape” has, up to
now, been very limited. Although several versions of the tape have been constructed there exists
very little quantitative data on its adhesion properties and even less on its self cleaning
properties. Using carbon nano pillars our research efforts will explore the balance between
adhesion and self cleaning in order to find a productive combination.
Beginning with a variation of pillar sizes and patterns we will experiment with the force
of adhesion for each sample and re-test after the samples have been soiled and cleaned using
mechanical cleaning principles. In nature the Gecko’s feet, which are covered in millions of tiny
hairs called setae, use frictional forces when slid against a surface to “stick” to the substrate.
Even after tracking dirt and debris the Gecko’s feet are clear of grime and ready to “cling” after
just a few steps. In order to mimic this, a symmetry of adhesion and mechanical cleaning must be
found in the nano pillar placement. This harmony will allow the adhesive to be used in a plethora
of occupations.
Introduction
Inspired by the evolutionary marvel that is the Gecko, a super adhesive, “Gecko Tape”
models the friction created by the microscopic hairs covering this lizard’s feet. The setae are not
“sticky” to the touch and do not attach to a surface when pressed to it, instead the hairs
enormously increase friction against the surface when slid against it. This creation of friction is
an example of the projects primary concept, the Van der Waals interaction.
Using this concept experimental versions of the tape are built with carbon nano tubes
mimicking the setae of the Gecko’s feet. The nano pillars allow the Van der Waals interaction to
be replicated between the surface and the tape. When the tape is slid against a surface the pillars
are activated, bending against the surface and creating the friction needed to suspend the weight.
The greater weight required for the tape to support the more nano pillars are activated.
Diagram courtesy of “Smart Gecko Tape”
Prof. Ronald Fearing
The most intriguing aspect of the tape is that it will increase the number of active pillars when
more weight is held. This is in fact, “smart tape”, able to hold more weight as more is added by
increasing the contact area. When the weight is removed from the tape the frictional forces
between it and the surface virtually disappear and the tape can be peeled away with out damage
or leaving residue.
With the concept of a super tape the number of applications become clear, however the
key in this project is re-use. The greatest challenge for research in this field is how to clean the
tape. Dirt particles get pushed into the spaces between the nano pillars and limit the movement of
the pillars required to create the frictional forces. The tape must be cleared of dirt so that the
pillars can again be activated and the tape can be “stuck” some place else. Self mechanical
cleaning is the ideal solution to this problem. The patterns of the nano tubes attached to the
backing with either lend themselves to efficient cleaning or make it nearly impossible to remove
dirt. Mechanical cleaning occurs when the tape is pressed perpendicular to a surface. No friction
is generated from this method and the pillars can be shifted enough to expel dirt particles.
Geckos in nature regain upwards of 70% of their original adhesion force after a few steps,
mechanical cleaning of tested microfibers have resulted in a minimum of 90% of the original
adhesion. Gecko tape has thus far been constructed at two extremes. A larger number of pillars
per square millimeter will create a greater adhesion and a fewer number will create greater self
cleaning properties. Currently there exists no standard or documented method for combining the
nano tubes in a way that will optimize adhesion and allow for dirt to be expelled from the pillars.
This experiment aims to document a standard pattern of uniformly sized nano tubes that will
have both optimum adhesion power and the ability to clear it’s self of dirt.
Experiment
Carbon nano tube based Gecko tape is primarily centered on re-use of the tape. The
pattern and orientation of the uniform nano pillars is vital to balancing mechanical self cleaning
and adhesion. An ideal sample of tape will maintain all of its original adhesion force after
mechanical cleaning. Finding the correct orientation of the pillars on the backing will allow for
both significant adhesion consistent over many uses.
Beginning with the findings of Kellar Autumn, which yielded a tape with large original
adhesive forces and significantly smaller forces after each use, we will use Polypropylene to
grow the initial carbon nano tubes to replicate his results. Polypropylene is a hard, non tacky,
wear resistant material ideal for the pillars. Autumn uses about 42 million pillars per square
centimeter, each pillar ranging from 10 to 15 micrometers long with a standard diameter of 0.6
pm. These pillars were tested to support a maximum load of 200 nanonewtons each. The
maximum load of the tape decreased largely with each use.
390µm Carbon Nano pillars used in a version of gecko tape producing a large adhesive force.
Arif Sirinterlikci
"Synthetic Gecko Tape."
After replicating Autumn’s result, we will experiment with a variety of lengths and
diameters for each pillar. In experiments with microfibers several small groupings of fibers were
ideal for mechanical self cleaning. We will combine orientations for maximum adhesion and
optimal self cleaning to attain a tape that can be reused multiple times with out losing notable
percentages of the original adhesion forces.
Each sample orientation will be tested by transferring the nano tubes onto a stiff backing,
applying the tape to a glass surface and testing the maximum adhesion power with a force gauge.
The samples will then be soiled with silica particles; mechanically self cleaned, and then tested
again while attached to the glass for its new maximum adhesion force. The samples will be
microscopically analyzed for a count of the remaining silica particles. These tests will result in
recorded data documenting the adhesion and self cleaning properties of the variation of sizes and
patterns for the nano tubes.
Close up of a gecko’s foot that clearly shows the pads that are covered in setae.
Toon, John.
"Dry Adhesive Based on Carbon Nanotubes Gets Stronger, with Directional Gripping Ability."
Anticipated Outcome
The data obtained from the tests of the carbon nano pillars will contribute to the
development of a pattern of pillars that result in consistent adhesion forces over multiple uses.
We will be working to find a series of “balanced” tapes that offer sufficient adhesion and well
working self cleaning to achieve a multi use tape.
References
Autumn, Kellar. "AutumnLab Publications." Kellar Autumn.com. Web. 27 Oct. 2009.
<www.KellarAutumn.com>.
Autumn, Kellar. "Evidence for Van der Waals Adhesion in gecko setae." PNAS 99.19 (2002).
PNAS. Proceedings of the Nationals Academy of Sciences of the United States of
America, 27 Aug. 2002. Web. 30 Oct. 2009.
<http://www.pnas.org/content/99/19/12252.full.pdf+html>.
Fearing, Prof. Ronald. "Smart Gecko Tape." Gecko Inspired Adhesion. University of California,
Berkeley. Web. 28 Oct. 2009. <http://robotics.eecs.berkeley.edu/>.
Hansen, W. R., and K. Autumn. "Evidence for self cleaning setae." PNAS. National Academy of
Sciences of the United States, 3 Jan. 2005. Web. 30 Oct. 2009. <http://www.pnas.org/>.
Knight, Will. "Gecko Tape Will Stick You To The Ceiling." Sounding Circle. 1 June 2003. Web.
29 Oct. 2009. <http://soundingcircle.com/>.
Sirinterlikci, Arif. "Synthetic Gecko Tape." Manufacturing Engineering July (2009). Print.
Toon, John. "Dry Adhesive Based on Carbon Nanotubes Gets Stronger, with Directional
Gripping Ability." Georgia Tech Research News. Georgia Technical University, 9 Oct.
2008. Web. 28 Oct. 2009. <http://gtresearchnews.gatech.edu/>.
"What is Directional Adhesive (Gecko Tape)?" Biomimetic World. Web. 30 Oct. 2009.
<http://www-cdr.stanford.edu/>.
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