Superhydrophobia spawns the Lotus Effect

Ever notice a dirty lotus leaf? How about a wet one? Of course you haven't. Lotus leaves are so hydrophobic that they can be dry in a rainstorm, while still using the rainstorm to clean themselves off. Now nanotechnology developers are trying to mimic the Lotus Effect.

The Lotus Effect has been intriguing technology developers from the moment they noticed that computers and water don't mix. Lotuses, which any nerd who was once into Egyptology or Egyptian mythology knows very well, are flowering plants that grow in water. Like many things that grow around water, they've developed ways to keep from getting waterlogged, and to channel water droplets to the places where they will be most useful. Lotuses manage it by making their leaves extremely hydrophobic.

Hydrophobic materials are materials that repel water. You see them in everyday life. Sometimes you'll have noticed that water in a glass or bowl curls upwards just where it meets the bowl's surface, seeming to climb the sides a little. The material that that bowl is made of is hydrophilic - water loving. If the water dips down as it meets the surface of the bowl, the material is hydrophobic. The lotus leaf is an extreme version of this. Water drops form beads on its surface, seemingly no matter how big or small the water drop is. If there's any curve to the surface, the water will roll off, leaving no droplets behinds. Lotus leaves are so good at this that they can remain dry during a rainstorm, flicking away water as fast as it comes down.

Superhydrophobia spawns the Lotus Effect

The secret to the lotus's talent at staying dry in the rain seems to be the tiny wax crystals that coat their surface. Wax is a good hydrophobic material in the first place, but the shape and size of the crystals counts. At one nanometer, they're small enough not to impede the progress of the drops as they move, but they're rough enough to be felt. Water tends to have a tough time adhering to a rougher surface. The roughness of the crystals also explains the self-cleaning properties of the lotus. Although repelled by the leaf itself, water can be attracted to dirt and grit lying on the leaf. It picks these things up as it makes its getaway. A perfectly smooth surface lets the small droplets slide along until they pick up the maximum amount of dirt on their lower surfaces and can't grab anymore. The tiny bumps of wax roll the droplet over and over, letting all possible surfaces be exposed to the dirt.

This sounds like a dream to many people who find their technology getting dusty over time. Wouldn't it be wonderful if it could be hosed down, letting water take the dust away, and then be perfectly dry moments afterwards? And of course, it would be nice to have a car that can be completely cleaned with a heavy fog or the slightest spritz of a hose. It will be some time before we come up with that, but companies are working on sprays and surfaces that mimic the outer coating of a lotus. Who knows, on day we may even be able to spray it on ourselves.

Top Image: William Thielicke

Second Image: Ahenobarbus

Via Nanotechweb, ABC, and Scientific American.