The pitcher plant is an insect-munching vine found lurking in some Asian forests. The plant has modified leaves that grow into bulbous jugs with a slippery mouth, leading to a pool of juices at the base. Insects land at the mouth of the pitcher and find themselves sliding into the enzyme soup and turning into short-order pitcher-plant dinner.
The deviously slippery sides of the pitcher plant flask are lined with stacks of ill-fitting cells, built with gaps and ridges, like badly laid paving stones. The plant fills the gaps in between with a sap, held in place by the ridged surface. Coating the mouth in a liquid film, the sap smoothens the unfortunate bug’s descent into into the plant’s waiting belly.
A synthetic coating that mimics the inside structure of the plant could keep wind turbine blades, air plane wings, power lines, and other large outdoor metal surfaces ice-free. Built like the pitcher plant slip-and-slide, this ice-proof synthetic material is made of a porous Teflon base which traps lubricant in pockets between overlapping fibers. The locked-down lubricant forms a continuous, ultra-slippery liquid layer that stands guard over the surface that needs protecting.
The first version of SLIPS (short for "slippery liquid-infused surfaces"), which its creators showed off for the first time last year, worked great on walls (making them graffiti proof), on medical surfaces (decreasing the chance of contamination), on wood (to keep a roof, say, ice-free), repelling everything from blood to oil to spray paint.
But one of the more appealing (and lucrative) applications of SLIPS that they’d observed, was not in preventing kids from tagging but in keeping things outdoor ice-free. Of course, there was a catch. SLIPS 1.0 wouldn’t stick on metal surfaces, which meant a host of potential beneficiaries—metal gates, aircraft wings, the vulnerable insides of a refrigerator freezer box—were missing out on the SLIPS effect and icing over en masse.
That’s what the team’s new work, published (PDF) recently, addresses. Lead researcher Joanna Aizenberg and crew at Harvard’s Wyss Institute have now modified the SLIPS coating to conquer that last holdout, metals.
The team tested their new coating on aluminum, a commonly used industrial metal. They found that ice forming was reduced, and the ice that did form slid off when the aluminum surface was tilted slightly. Coated with this extreme antifreeze, blades of wind turbines or airplane wings can be protected against frosting or icing over—with a tilt and shake, the layers of ice will simply slide off.