University of Amsterdam (UvA) researchers Hans Terwisscha-Dekker, Marion Grzelka, Simon Lépinay and Daniel Bonn investigated the workings of gecko tape.
Gecko, a small animal known for the phenomenal adhesive strength in its feet, which allows it to walk on walls and even ceilings. The phenomenon led to ‘gecko tape’, a strongly adhesive DIY tape. Its name suggests that the tape and the gecko stick in similar ways.
Adhesion Caused by Pillars in its Feet
For the gecko, its stickiness, or adhesion, is caused by small pillars in its feet. The electric forces between the molecules in those feet and the surface on which the gecko walks – the Van der Waals forces – allow the gecko to stick to almost any surface.
Over the past years, a lot of research was carried to create synthetic versions of this system – and seemingly with success: one can now buy ‘gecko tape’, a double-sided tape of which the name at least suggests that it uses the same principles as gecko feet.
UvA researchers studied the surface of the tape using a microscope and indeed saw small pillars, similar to those in the gecko’s feet. Next, they measured the adhesion energy between gecko tape and glass.
Gecko Tape Stickier than Double-sided Tape
It became clear that gecko tape indeed is stickier than normal double-sided tape on glass. Next, they studied whether the gecko tape physics also the same as that of the gecko feet. After the researchers had removed the pillars of the gecko tape’s surface, there was a surprise: the tape still showed the same amount of adhesion. It seemed something was happening that had little to do with the gecko.
The researchers studied the contact surface between the tape and the glass during the experiment – that is the amount of microscopic surface where the two materials truly touch. It turned out that, with and without the pillars, there was a much bigger contact surface between the gecko tape and the glass than in the case of ordinary double-sided tape. Per unit of area of ‘true contact’, both kinds of tape were more or less equally sticky.
The pillars on the gecko tape do not play a role in its adhesive strength. This in stark contrast with the gecko itself, which makes essential use of the surface structure of the pillars. Despite its similarities with the real gecko, gecko tape, therefore, works in the same way as ordinary tape: the adhesion is caused by glue, not by Van der Waals forces.
It turns out that it is the tape’s softness that makes its contact surface bigger than that of normal tape, causing it to be stickier. That in turn does correspond to what the gecko does: using the pillar structure, the animal also maximizes the contact surface – even though it uses very different physics to achieve this.
Source: University of Amsterdam