A group of researchers from the University of Illinois at Chicago, Syracuse University, and the University of Pennsylvania developed a method for demonstrating how a specific material wrinkles after being flattened. The group describes experiments they conducted with tiny pieces of plastic in a paper published in the journal Nature Physics.
Prior research has shown that understanding the rules of wrinkling for almost any material is difficult—there are simply too many variables to get a handle on. The researchers wanted to know how wrinkling works in a single material as it wrinkles in a controlled environment.
The research built on the work of Ian Tabasco, a mathematician at the University of Illinois Chicago. He devised a theory based on the energy costs associated with material wrinkles. To put Tabasco’s theories to the test, the researchers first created simulations of material responses to prodding in ways described by his math formulas. However, they discovered that a simulated environment was ineffective, so they created a real-world testing scenario.
They spun thin, flat pieces of plastic onto a curved glass surface, making the plastic even thinner as it took on the shape of the curved glass. The curved plastic pieces were then placed on a wet surface and the water tension caused the plastic to wrinkle. They then fine-tuned the simulations using data from the wrinkles that formed, and discovered that doing so repeatedly resulted in the generation of rules that described how wrinkles appeared and behaved.
The researchers discovered that wrinkles forming in rows rather than on the edges of a patch were dependent on the shape of the piece of plastic just prior to wrinkle formation. They also discovered that by dividing the plastic area into many small subunits, they could predict where wrinkles would appear in a given piece of plastic. They discovered that under these conditions, Tabasco’s calculations could be used to describe the types of ripples that would appear and cause wrinkling.