April 15, 2005

NC State Engineers Create Wrinkles for Research

The image shows the wrinkles created in Genzer’s lab (far left) along with other examples of naturally occurring wrinkles. (Image courtesy of Dr. Jan Genzer)

At NC State University engineers in the Department of Chemical and Biomolecular Engineering are exploring the possible benefits of wrinkles — how to create them, how to control them and how to use them. Typically, wrinkles, or buckles, in surfaces are considered a major design flaw that destroys the usefulness of the surface. For example, in silicon chips, wrinkled surfaces are a defect that sends a chip to the trash. But in the laboratory of Dr. Jan Genzer, associate professor of chemical and biomolecular engineering, the wrinkle has become the object of exploration for possible uses.

The inspiration for the research came as an added benefit to another experiment. The researchers were attempting to harden a sample of silicon rubber but created instead a hardened wrinkly surface. “What we found when we examined the surface,” says Genzer, “was that our surface was decorated with multiple generations of self-similar wrinkles, with each new generation ‘carrying’ the old one — basically, the wrinkles have their ‘infant’ wrinkles, which have their ‘infant’ wrinkles, and so on.” The researchers were able to observe five distinct generations of wrinkles that span six orders of magnitude in dimensions ranging from tens of nanometers to millimeters.

Most people would ask, “Why this would be important?” However, engineers ask, “How can we use this phenomenon?” That is what Genzer and a senior research associate, Dr. Kirill Efimenko, are exploring, now that they know how to form the multigeneration wrinkles consistently.

“We can control the creation and wavelength of the wrinkles by manipulating the surface,” says Genzer. “We stretch a flexible elastomeric surface, convert the top-most part of the specimen into a more rigid skin by exposing it to ultraviolet/ozone treatment and then gradually release the tension.”

Genzer and Efimenko collaborated with scientists from Harvard University and Pennsylvania State University to uncover the mechanisms that lead to the formation of multigeneration wrinkles.

What will they do with the wrinkles?

“That is the challenge we face right now,” says Genzer. “Now that we know how to create such complex surface topologies repeatedly, we have to establish how we put them to use? We have already used them to sort tiny beads by size. The next most logical application would involve something like tunable optical gratings or surfaces with the ‘lotus leaf’ effect.”

Genzer recently published his article, “Nested Self-similar Wrinkling Patterns in Skins,” in the journal Nature Materials.

— weston —

Media contact:
Jennifer Weston, (919) 515-3848, weston@ncsu.edu

Technical contact:
Dr. Jan Genzer, (919) 515-2069, Jan_Genzer@ncsu.edu

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