Scientists at Harvard University have created a material that repels just about any type of liquid, including blood and oil, and does so even under harsh conditions like high pressure and freezing temperatures.
The bio-inspired liquid repellence technology, described in the Sept. 22 issue of Nature, should find applications in biomedical fluid handling, fuel transport, and anti-fouling and anti-icing technologies. It could even lead to self-cleaning windows and improved optical devices.
“Inspired by the pitcher plant, we developed a new coating that outperforms its natural and synthetic counterparts and provides a simple and versatile solution for liquid and solid repellency,” says principal investigator Joanna Aizenberg, Amy Smith Berylson Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS), director of the Kavli Institute for Bionano Science and Technology at Harvard, and a core faculty member at the Wyss Institute for Biologically Inspired Engineering at Harvard.
By contrast, current state-of-the-art liquid repellent surfaces have taken cues from a different member of the plant world. The leaves of the lotus resist water owing to the tiny microtextures on the surface; droplets balance on the cushion of air on the tips of the surface and bead up.
The so-called lotus effect, however, does not work well for organic or complex liquids. Moreover, if the surface is damaged or subject to extreme conditions, liquid drops tend to stick to or sink into the textures rather than roll away. Finally, it has proven costly and difficult to manufacture surfaces based on the lotus strategy.
The pitcher plant takes a fundamentally different approach. Instead of using burrlike, air-filled nanostructures to repel water, the plant locks in a water layer, creating a slick coating on the top. In short, the fluid itself becomes the repellent surface.
“The effect is similar to when a car hydroplanes, the tires literally gliding on the water rather than the road,” says lead author Tak-Sing Wong, a postdoctoral fellow in the Aizenberg lab. “In the case of the unlucky ants, the oil on the bottom of their feet will not stick to the slippery coating on the plant. It’s like oil floating on the surface of a puddle.”
Inspired by the pitcher plant’s elegant solution, the scientists designed a strategy for creating slippery surfaces by infusing a nano/microstructured porous material with a lubricating fluid. They are calling the resulting bio-inspired surfaces “SLIPS” for slippery liquid-infused porous surfaces.