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October 2019
 

Nano-Enoki Mushroom Surfaces
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.


Enokitake Mushrooms

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
2 This video shows how dried mustard can be flicked off the nano-enoki surface. Here's a similar video but with dried blood.
 

Lab Services
We have many customers who have only a limited need for contact angle analysis. Others are unsure of their future need but currently are interested in having some samples tested. Whatever the case may be, we offer professional lab services here at our New Jersey facility for surface science tests. We can measure contact angle, roll-off angle, advancing and receding contact angle, contact angle hysteresis, surface energy, surface tension, and interfacial tension. More advanced dynamic and time-dependant studies may also be possible. Talk to us about your requirements.

Should you or your organization have a need for professional surface testing, our lab is available. We have over 50 years building and using the world's finest contact angle goniometer and tensiometer products. If you are looking for reliable data, prompt and professional service, and the confidence that your results were produced using state-of-art instrumentation from ramé-hart, look no further. We strive to meet or exceed your expectations. We offer one-week turn around and expedited handling is available for a small additional fee. Over the past few years, we've done fee-based lab work for hundreds of pleased customers. Many are repeat customers and many go on to purchase a ramé-hart instrument from us. To learn more about our professional lab services and how we can help you, visit this page. Also, please contact us if you have a current testing need. We look forward to hearing from you.

 
 
Regards,

Carl Clegg
Director of Sales
Phone 973-448-0305
www.ramehart.com
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