An engineering team at Duke University has invented a process that can change the texture of a soft polymer by changing the voltage applied to it. The plastic's surface texture can be switched from rough to smooth, and back again, in a few milliseconds.
The standard process for texturizing plastics, electrostatic lithography, is a permanent one that uses an electrode located above the polymer to etch patterns onto its surface. Once those patterns have been etched, they can't be changed. The Duke team found that it could change surface textures from dots, to circles, to lines, to smooth over large and curved areas by applying different voltages.
The dynamic electrostatic lithography process changes a plastic's surface texture to patterns with various shapes and sizes, or smooth, in a few milliseconds. (Source: Duke University)
Xuanhe Zhao, assistant professor of mechanical engineering and materials science at Duke’s Pratt School of Engineering, who led the team, said in a press release that possible applications of the new dynamic electrostatic lithography process could include climbing or gripping gloves that change texture and smoothness on demand as they adapt to varying surfaces. Other uses might include creating surfaces that are self-cleaning and water-repellant, or that serve as platforms for devices that deliver drugs in a controlled release. Additional applications could be in technologies such as microfluidics and camouflage.
"We invented a method which is capable of dynamically generating a rich variety of patterns with various shapes and sizes on large areas of soft plastics or polymers," Zhao said. "The changeable patterns we have created in the laboratory include circles and straight and curved lines, which are basic elements of fingerprints. These elements can be dynamically patterned and changed on a glove surface that covers fingertips."
"This new approach can dynamically switch polymer surfaces among various patterns ranging from dots, segments, lines, to circles," said Qiming Wang, a student in Zhao’s laboratory and the first author of the paper describing the team's results. "The switching is also very fast, within milliseconds, and the pattern sizes can be tuned from millimeter to sub-micrometer."
Zhao's earlier experiments showed that as an applied voltage increases, polymers tend to start creasing, which eventually leads to the formation of large craters. The research helps explain, for example, why polymers used to insulate high-voltage electrical wires tend to fail over time.
Other members of the current engineering research team included undergraduate student Mukarram Tahir and postdoctoral fellow Jianfeng Zang. The Duke study was
supported by the Research Triangle
Materials Research Science and Engineering Center, which is funded by the National Science Foundation. Additional support came from the Lord Foundation and a Haythornthwaite Research Initiation grant.
Wow! Combine this research with Berkeley's Gecko Project and there is a possibility of on-demand adhesion. I could spend all morning dreaming about possible applications for such a substance. I can also see this being used for aerodynamic applications... dynamic vortex shedding for variable drag profiles -- both high-speed and high-drag configurations from the same wing without flaps or geometry adjustment... sonic boom reduction... stealth radar deflection... underwater propulsion... oh my!
On-demand television programming, on demand software, now plastic material that can adapt on demand. Very sci-fi, but as William notes, tons of possible applications. The real test will be in the design of the systems that can deliver the voltage changes to modify the surface texture. That's the real design challenge for any of these applications.
Thanks, williamlweaver, for your response. I had the same initial reaction, and my husband told me about the Gecko Project. After writing this, we saw the latest Mission Impossible via Netflix, and when Tom Cruise's right hand glove quits at 120 stories, I thought of this discovery.
Nadine, glad you liked the article. I had a similar experience contemplating applications when I first heard of this discovery: I felt like my head almost exploded with the number of possibilities.
For those who are interested, here is a link to the article by Zhao. The polymer needs to be fairly soft (modulus less than 1450 psi) -- although electrostatic lithography requires materials which are much softer still. Zhao's group used a silicone rubber. It was bonded to a more rigid polymer film (Kapton), which in turn was bonded to a metal electrode. On the other side of the silicone was what Zhao describes as a "transparent conformal electrode" (actually a 20% salt solution).
This is definitely an interesting phenomenon which could have all kinds of potential applications. Zhao's group is doing a lot of fascinating work, and it's great to see it being discussed outside of academia.
One possible application would be power tool grips. When the tool is not in use, it could be smooth, so it could be easily cleaned. During use, it could be then be textured for non-slip grip.
Thanks for the additional links, Dave. And ChasChas, I think that's a brilliant usage idea for a material that can change texture on demand, except at this point we're only talking soft plastics not hard, durable ones used in structures. I wonder how difficult it would be to extend this idea to rigid plastics, or find a different method that worked with them.
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