Pitcher plant-inspired liquid repellent
Inspired by the insect-eating pitcher plant, scientists have created a material capable of repelling almost any liquid, including blood and even crude oil.
Dubbed "slippery liquid infused porous surfaces", or SLIPS for short, the new materials are inspired by a natural phenomenon. Carnivorous pitcher plants catch flies and other insects by crafting a specialised surface that traps a layer of water against itself. This repels the oil on the feet of visiting insects, causing them to slide helplessly into the plant's pitcher of digestive juices.
Harvard scientist Joanna Aizenberg and her colleagues have copied this design, creating a microporous surface made of Teflon to which a fluorine-rich organic inert liquid called Fluorinert FC-70 is added. The liquid spreads out across the surface, coating the Teflon, by capillary action and locks into place within the pores. But as it doesn't mix with oil or water-based substances, any liquids - and even ice - that land on the surface form droplets and slide off. And because liquids are incompressible, the new SLIPS-endowed surfaces remain functional even under very high pressures. The team successfully tested them to 767 atmospheres, which was the highest pressure they could generate in their laboratory.
Critically, previous attempts to build liquid-repelling, high-slip surfaces have been modelled on a different plant: the lotus leaf. This uses a system of tiny pillars to trap a layer of air against the leaf surface, causing it to shed water and dirt. But the system is easily compromised by physical damage and liquids with low surface tension simply displace the air rendering the surface useless.
The pitcher-inspired SLIPS, on the other hand, being based on a trapped liquid rahter than air, do not suffer this drawback and are also far more resilient. In fact, when the surface is damaged it effectively "self-heals" when the liquid flows back into the abraded area.
Consequently, Aizenberg and her colleagues, who have described the work this week in the journal Nature, are optimistic that the surfaces will remain super-slippery and liquid repellent even under extreme conditions. Possible applications include uses in deep-sea drilling rigs, safer fuel transportation, anti-icing coatings and even anti-graffiti measures...