Eindhoven University of Technology (TU/e) and University of Twente researchers studied the unpeeling of looped adhesive tape and developed a new model explaining the removal of troublesome loops and blisters (tiny air pockets) in adhesive tapes.
Imagine a tape where the two sticky sides are stuck together resulting in a loop. If you try to remove the loop by pulling the two loop ends the size of the contact area between the sticky sides starts to decrease but the loop doesn’t then unloop as you might expect. Instead, as you peel the two sides apart, the loop just shrinks in size until it reaches a critical small size and then eventually unloops.
Studying Evolution of Loops in Different Tapes
Removing loops and blisters has implications for more than just band-aids and sticky tape, as Jacco Snoeijer, Faculty of Science and Technology, University of Twente, points out. “When working with materials for thin flexible electronics and soft robotics, it’s important to know what forces should be applied to remove blisters or loops. Otherwise, you face the prospect of permanently damaging the material."
To study how loops, change when subject to varying peeling forces and velocities, the researchers decided to study how loops evolved in different tapes. But they needed a reliable way to make straight tape loops in the lab.
“In straight tape loops, the two sticky sides of the tape are perfectly aligned or parallel. If the two sides were not parallel, the loop would twist as the size decreased, and we wanted to avoid any twisting physics,” said Twan Wilting, a Ph.D. candidate in the Fluids and Flows group in the department of Applied Physics at TU/e working with Hanneke Gelderblom. “As we didn’t have automated devices, we had to make the loops by hand.”
Model Breakthrough for Real-world Loops
Once the unpeeling experiments had been complete, the researchers used the observations to construct a new model that describes the loop shrinkage process and gives an indication of the critical loop size (before final unlooping) and the critical peeling force.
“The model matches the experimental observations very well. Perhaps in the future, we’ll add more to the model, particularly on how the adhesives evolve during unlooping,” said Snoeijer.
It’s one thing to remove loops in specially prepared tapes, but it’s another thing to remove loops in practical settings. Wilting and the researchers know there are plenty of applications for their model in the real world: “Blisters and loops occur in multi-layered coatings, flexible electronics, soft robotics, even during the production of graphene (the material made of carbon atoms in a honeycomb lattice that is one carbon atom thick). This means you need to know what happens during folding and self-adhesion processes, and that’s where our model can certainly help.”
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