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October 2019 |
| Nano-Enoki Mushroom Surfaces |
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If you've ever traveled to Japan, you
may have enjoyed soup made from enoki, a skinny white mushroom which
is popular in Asian cooking. Inspired by the enoki, researchers at
the University of Pittsburgh are developing a plastic material that
can be made superomniphobic by producing nano-enoki mushroom-shaped
structures on the surface.1 What's most amazing is the potential
durability of these surfaces. Test surfaces have exhibited contact angles in excess of 150° with a contact angle hysteresis lower than 20° for many different liquids. The base material is optical PET (polyethylene terephthalate). Unlike some plastics like PTFE which has a water contact angle in the 109° neighborhood, a smooth PET surface is hydrophilic with a water contact angle just over 70°. However, by adding these tiny mushroom-shaped asperities, which are only a couple of microns apart, the surface becomes incredibly repellant to not only water but most liquids - coffee, milk, ketchup, and pancake syrup. For example, both blood and mustard, even left to dry, would flake off these nano-enoki surfaces without leaving any trace of residue.2 As you may imagine, it's the nano-topology that induces a Cassie-Baxter state. That is, the liquid sits atop the mushroom heads without falling down and in between them. This is what promotes the high contact angle. In addition to being superomniphobic, the optical transmission properties remain virtually undisturbed although the haze values increase significantly. These surfaces may not be optimal for applications like lenses and windows, but they could be suitable for solar panels and LED applications. Unlike many experimental superomniphobic surfaces that have been proposed and tested, the nano-enoki surface is amazingly robust and bendable. In fact, preliminary tests suggest that these materials can undergo thousands of bending cycles without losing any repellency or optical qualities. This level of durability is rare in the arena of superhydrophobic nano-textured surfaces. “The lotus leaf is nature’s gold standard in terms of a liquid-repellant and self-cleaning surface,” says Paul Leu, PhD, associate professor of Industrial Engineering at the University of Pittsburgh Swanson School of Engineering and at whose lab this research was conducted. He continues, “We compared our nano-enoki PET with a lotus leaf and found that ours was better at repelling more kinds of liquids, including olive oil, blood, coffee, and ethylene glycol. The surfaces not only resist staining from various liquids, but may be adapted for medical applications to resist bacteria or blood clotting.” 1 Sajad Haghanifar, Luke
M. Tomasovic, Anthony J. Galante, David Pekker, Paul W. Leu.
Stain-resistant, superomniphobic flexible optical plastics based on
nano-enoki mushroom-like structures. Journal of Materials Chemistry
A, 2019; DOI:
10.1039/C9TA01753D |
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Regards,
Carl Clegg |
