Washington (ISJ) – A new research has unfolded the secret of wrinkling, folding and creasing. Ever wondered, why layered materials sometimes form one kind of wrinkly pattern or another or even other variations, such as creases, folds, or delaminated buckles.
Researchers at Massachusetts Institute of Technology (MIT) have found the underlying process is the same in all of these cases. Layers of material with slightly different properties ? whether skin tissue or multilayer materials created in the lab ? tend to form patterned surfaces when they shrink or stretch in ways that affect the layers differently.
But the new analysis, for the first time, creates a unified model that shows exactly how the properties of the individual layers, and how they are bonded to each other, determines the exact form of the resulting texture.
The analysis says the patterning process applies to everything from the folds on the surface of the brain to wrinkles on an aging face, and from the buckling of tree bark to the ridged skin of a pumpkin.
The study has been carried out by MIT associate professor of mechanical engineering Xuanhe Zhao and postdoc Qiming Wang.
The researchers say it will become easier to design synthetic materials with exactly the kinds of surfaces needed for specific applications ? such as better traction, or water-shedding properties ? by understanding the factors that produce these patterns. According to Zhao, the work could also lead to a better understanding of many biological processes, including the growth of plants, animals, microbial colonies, and organs in the body.
The work began with a classification of patterns into specific categories: wrinkles, creases, folds, period doubles, ridges, and delaminated buckles.
Wang says wrinkles have a relatively uniform wavy shape while creases are sharp indentations like those seen on the brain?s surface. ?Delaminated buckles? form when layers start to come apart, as on the bark of a tree, and ?ridges? form relatively narrow, spaced-out peaks.
Describing each of the forms as a different ?phase? of the layered material, the researchers then created a three-dimensional phase diagram that shows how three basic characteristics of the layered material ? having to do with the relationship between different materials? expansion or shrinkage, rigidity, and how tightly bonded they are ? lead to these different outcomes.
Using this diagram, Zhao says, ?We can quantitatively predict which state a surface will fold into, so you can design the pattern you want.? These same principles ?apply to various length scales, from very small to very large,? he adds.
?Now, we can guide the design of new patterns and functions,? Wang says, ?by going to a set of parameters predicted by the model.?
Zhao and Wang tested their model by comparing its predictions to a wide variety of different materials in the lab and previously reported results, and found that it agreed very well with experimental data. ?The surprising thing is, with so many complicated shapes, now you can just use one system, one understanding? to explain variations, Zhao says. ?This is the simplest model that explains all these patterns.?
The researchers expect that this model will not only be helpful for understanding growth and aging patterns in biological organisms, but could help in the design of materials for disease treatment, cell cultures, control of biofouling, controllable properties of water shedding, and flexible electronic materials.
