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How Do Water Striders' Legs Repel Water? Science Has An Answer

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Sometimes the best solution for human problems comes from the animal kingdom. Take creating the perfect water repellent surface: this is something done naturally by insects known as Gerridae, or water striders.

Water striders have tiny hairs all over their bodies, which provides resistance to water droplets, allowing them to not just repel water, but also to prevent that water from weighing down their bodies. This allows the insects to run across the surface of the water without sinking.

Because of their unique properties, water striders are often found in high-humidity climates, where they face the challenges of both liquid water and vapor.

But exactly how do these tiny hairs allow water striders to exist so and to skim along the surface of water? A team of Chinese scientists recently decided to study water striders at the nanoscale and find out.

Scientists began by taking images of water striders with a video camera that allowed them to zoom in and study the details of the insects' legs, particularly searching for how they repel water. They put one of the water striders' legs in a high humidity environment and recorded how it worked in repelling water with high-speed photography.

Researchers also studied the microscopic conical-shaped hairs on the water strider's legs and captured them with X-ray tomography and electron microscopes. They noticed that each hair had "nanogroves" where water condensed and moved away from the tips of the hairs.

"First, droplets migrate inside the texture and grow," writes the study authors. "Then, drops are suddenly expelled out of the hairs, owing to the elastic deformation of the network of setae [stiff bristles] by growing drops. Ultimately, condensed drops are expelled from the leg."

Once exposed to a certain amount of water drops, the droplets push away the hairs they come into contact with and get expelled to the top of the hair again.

"We anticipate that the self-removal behavior of droplets on Gerris legs will inspire the design of novel, robust superhydrophobic materials for many practical applications, such as self-cleaning surfaces, antidew materials, drop-wise condensers, and microfluidic devices," write the authors. Striders are in the insect class in the Gerriade family and of the Gerris genus.

The ability of water striders and other insects to walk on water recently inspired scientists to design a robot based on those properties.

Photo: Rubén Díaz Caviedes | Flickr

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