The mystery of the sticky tape loop
The model can be used in various applications in which the aim is to prevent adhesive layers coming apart, or, conversely, to remove loops and blisters, as is the case when stacking graphene layers, in electronics, or when designing screen protectors
When you press the two sticky sides of a piece of adhesive tape together at a single point, a loop forms. Try to pull the loop apart, and something odd happens. Instead of instantly springing open, the loop first gets much smaller, until the sticky tape finally releases. This phenomenon so intrigued TU/e researcher Twan Wilting that he decided to study it as part of his PhD work.
“It struck me that a sticky tape loop doesn’t immediately release if you pull at it, instead it first gets smaller,” he explains. “I thought, ‘huh, this is weird, how does that work?’” Wilting got in touch with various people on the internet, but no one knew the answer. “The fascination eased off a little, but the question stayed in my mind,” says the PhD candidate.
Wilting’s first step was to build an experimental setup equipped with a camera. This would enable him capture the best possible images of how sticky tape deforms when pulled apart. “I bought a range of sticky tapes – at the Hema, Jumbo, Action, and many more stores – to see if there was any difference between them,” he explains.
Next came the painstaking work of perfectly aligning the adhesive tape, before sticking it to itself to form a perfect loop.
“If one piece is slightly askew, the more you pull, the more the tape curls, and we don’t want that. This is very precise manual work.” All told, Wilting needed about half a kilometer of sticky tape to carry out his experiments.
In the lab, he shows the setup and explains how it all works. Once he has crafted a good loop in a piece of sticky tape, he attaches the tape to the machine (see image on right).
“Then you set a constant speed – anything from very slow to very fast – and the loop is pulled apart,” he says. Meanwhile the camera is capturing the sticky tape in profile. “We carried out various experiments, varying the time taken to pull the loop apart from 30 seconds to as much as twelve hours,” says Wilting. He discovered that the pull speed influences the curvature, and the size of the loop when it releases. “The faster you pull, the smaller the loop becomes before the tape comes apart.”
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