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

ord5003@psu.edu

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Jesse Gresh

108 Turner Hall

814.881.0353

jtg5057@psu.edu

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/>.