Peeling stickers inspire new path for stretchable electronics

For some, there's inspiration to be found in unremarkable daily minutia. A team of researchers who studied stickers peeling from windows say that what they've observed could lead to a new way to precisely control the fabrication of stretchable electronics.

Delamination demonstration - The tape detaches from the surface and forms blisters of uniform size and spacing (Credit: Donna Coveney)

A study published in the online edition of the Proceedings of the National Academy of Sciences (PNAS) this week offers a new approach to designing stretchable circuits that would enable electronic devices to be embedded into clothing, bendable displays, surgical gloves, and other flexible materials. The wiring in the circuits would be less prone to damage as the material twists and deforms, solving an engineering challenge that has mired the development of flexible electronics.

"It's something that's around you all the time - but if you look at it a different way you can see something new," says Pedro Reis, applied math instructor at MIT and senior author of the PNAS paper.

An MIT news item writes that the research team, which includes one at MIT, did not have stretchable electronics in mind when they launched the project, but rather focused on an analysis of of the wrinkling and delamination of stickers. The small blisters that appear in stickers attached to car windows are a common example of such delamination.

So how does the delamination of stickers help with bendable circuits? Well, before we get to that we need to consider the two causes of delamination. First, it occurs when you have different rates of heat-induced expansion between a thin film and the surface to which it is attached, such as the blisters formed in stickers attached to a window when exposed to sunlight. Secondly, the compression of the surface can also lead to delamination. As the surface is compressed, the film bends with it until it reaches a certain energy threshold, then pops away from the surface, forming small blisters.

MIT writes: "The researchers performed well controlled experiments to stretch and compress surfaces with thin films attached to them, and measured the dimensions of resulting blisters. From their experimental data, the team developed a theory to explain the formation, size and evolution of the blisters." In the video below, a a surface (pink) is compressed until the orange tape attached to it delaminates, forming blisters. (Video courtesy / Pedro Reis.)

What exactly did they find? The team found that the blister size is dependent on the elasticity of the film and the substrate and the strength of adhesion between them. Their model allows them to predict the size of the blisters that will form under specific conditions. This, in turn, subjects delimination to precise control by changing the strength of adhesion and the elastic properties of the film and wires.

"The researchers realized that by intentionally creating delaminated surfaces, they could design devices that allow wires attached to a surface to move with the material without breaking. If the wires are already partially separated from the material, they won't break under stress from twisting and stretching of the substrate," writes the article.

The new study implies that the use of ultra-thin, flexible but strong materials such as graphene are ideal candidates for stretchable electronic applications.

The work was funded by the EU-NEST (New and Emerging Science and Technology) program and the French Agence National Recherche.