Water, oil, blood and insects alike slide swiftly off a new super-slippery material inspired by a carnivorous plant.
快猫短视频s searching for clever materials sometimes borrow ideas from nature. Lotus leaves, for example, are famously water repellant, thanks to their textured surfaces which trap a cushion of air for water to slide down.
The leaves have inspired a range of so-called 鈥渟uperhydrophobic鈥� materials. But these materials have trouble repelling oils and more complex liquids, which have lower surface tensions than water and can seep into the surface at the slightest pressure.
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鈥淓verybody鈥檚 talking about the lotus leaf,鈥� says of Harvard University, whose lab designs and builds biomimetic materials to solve a range of problems. 鈥淏ut it鈥檚 just one of many strategies that nature created to manage and control the interaction with liquid.鈥�
Now, a new material takes a cue from one of the plant world鈥檚 few meat-eaters: the carnivorous pitcher plant Nepenthes . The plants prey on insects, whose oily feet normally allow them to walk up walls. But pitchers鈥� tube-shaped leaves have microscopic bumps that hold a thin layer of water in place. The water repels the oils, sending hapless insects slipping straight into their gaping mouths.
鈥淭hey just step on the rim, and immediately slide into the digestive juices,鈥� Aizenberg says.
Aizenberg realized that with the right choice of lubricating liquid, the pitcher plant鈥檚 strategy could be adapted to repel virtually anything.
The researchers started with a textured substrate, which could be almost anything that is rough on the nanoscale, Aizenberg says. One good choice is Teflon, a fibrous material that is widely thought to be super-slippery itself.
Filling in the bumps
Their most slippery surface resulted when they added a layer of the perfluorinated fluid 3M Fluorinert FC-70, manufactured by the firm 3M, to Teflon. The liquid oozed into all the pores in the Teflon, and left a nanometres-thin layer of liquid at the top. The material still feels dry to the touch, and other liquids simply hydroplane off the surface, like a car sliding off a wet road. The team calls the material 鈥榮lippery liquid-infused porous surfaces,鈥� or SLIPS.
鈥淲e call it SLIPS, because everything does,鈥� Aizenberg says. The materials could be useful for making self-cleaning windows, friction-free oil and water transport pipes, and safe and efficient blood transfusion devices, she adds.
SLIPS beat the lotus leaf in several arenas. They鈥檙e more slippery 鈥� liquids from water to oil to blood lose contact with the surface when it鈥檚 tilted by an angle as shallow as 2 degrees, whereas liquids held to other surfaces tilted from 5 to 30 degrees. They can also recover from damage, because the lubricating liquid naturally seeps back in to any holes. And because liquid is incompressible, the material can be used at pressures equivalent to 7 kilometres underwater.
鈥淚t鈥檚 interesting that it combines self-lubrication, self-healing and self-cleaning, which are different processes,鈥� says of the University of Wisconsin-Milwaukee. 鈥淚t鈥檚 a new type of smart material.鈥�
Journal reference: Nature, DOI: 10.1038/nature10447
