This new material pulls clean drinking water straight out of the air

Daniel Taeger/Shutterstock.com

This could solve a lot of problems.

One of the ways of sourcing drinking water in areas afflicted by drought is by harvesting it from the air, and now a new material developed by scientists in the US could make this tricky feat easier than ever.

Researchers at Harvard University have taken inspiration from a variety of water-collecting traits in different natural species to develop what could be an unrivalled composite system for harvesting and transporting atmospheric H20.

"Everybody is excited about bio-inspired materials research," said chemical biologist Joanna Aizenberg from Harvard's Wyss Institute for Biologically Inspired Engineering. "However, so far, we tend to mimic one inspirational natural system at a time."

Instead, the team's system combines elements from three distinct plant and animal species to create a material that they claim outperforms other synthetic surfaces designed to trap condensation.

According to the researchers, the major challenges in harvesting water from the air lie in controlling the size, speed, and direction of water droplets as they form and flow on a surface. At the core of their solution to this problem, the researchers copy the external bumps of Namib desert beetles, which help the insect to collect water droplets on its shell.

Aizenberg Lab/Harvard SEAS

Scientists already knew that the bumps' hydrophilic (water-attracting) tops and hydrophobic (water-repelling) surroundings helped them collect water, but Aizenberg's team realised that the convex shape of the protrusions themselves might also be able to harvest water too.

Using modelling, the team found that this natural water-trapping mechanism could be enhanced by mimicking the geometry and slopes of cactus spines, which help drive collected droplets down the slopes.

By combining this further with a nano-coating designed to emulate the slippery surfaces of pitcher plants, the material facilitates greater droplet formation as the water beads downwards.

"We experimentally found that the geometry of bumps alone could facilitate condensation," said one of the researchers, Kyoo-Chul Park. "By 

• optimising that bump shape through detailed theoretical modelling and 
• combining it with the asymmetry of cactus spines and 
• the nearly friction-free coatings of pitcher plants, 

we were able to design a material that can collect and transport a greater volume of water in a short time compared to other surfaces."

The tandem effect of the system – together with a technology developed by the researchers called Slippery Liquid-Infused Porous Surfaces – helps the material collect water in ways that could otherwise prove impossible.

"Bumps that are rationally designed to integrate these mechanisms are able to grow and transport large droplets even against gravity and overcome the effect of an unfavourable temperature gradient," the authors write in their paper, published in Nature.

Not only could this technique help to harvest water from the air in areas affected by water shortages, but it could also be of use to enhance condensation in industrial machinery.

"Thermal power plants, for example, rely on condensers to quickly convert steam to liquid water," said one of the team, Philseok Kim. "This design could help speed up that process and even allow for operation at a higher temperature, significantly improving the overall energy efficiency."

With about 1.2 billion people around the world living with water scarcity and two-thirds of the global population experiencing water shortages on a monthly basis, the potential of technology like this could make a huge difference to so many lives.

ORIGINAL: Science Alert

PETER DOCKRILL

7 MAR 2016

http://www.seas.harvard.edu/news/2016/02/pulling-water-from-thin-air

Pulling water from thin air

INSPIRED BY A DESERT BEETLE, CACTUS AND PITCHER PLANT, RESEARCHERS DESIGN A NEW MATERIAL TO COLLECT WATER DROPLETS

February 24, 2016

By Leah Burrows

An array of slippery asymmetric bumps shows a significantly greater volume of water collected at the bottom of the surface compared to the flat slippery surfaces. (Courtesy of the Aizenberg Lab/Harvard SEAS)

Organisms such as cacti and desert beetles can survive in arid environments because they’ve evolved mechanisms to collect water from thin air. The Namib desert beetle, for example, collects water droplets on the bumps of its shell while V-shaped cactus spines guide droplets to the plant’s body.  

As the planet grows drier, researchers are looking to nature for more effective ways to pull water from air. Now, a team of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University have drawn inspiration from these organisms to develop a better way to promote and transport condensed water droplets.

“Everybody is excited about bioinspired materials research,” said Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science at SEAS and core faculty member of the Wyss Institute. “However, so far, we tend to mimic one inspirational natural system at a time. Our research shows that a complex bio-inspired approach, in which we marry multiple biological species to come up with non-trivial designs for highly efficient materials with unprecedented properties, is a new, promising direction in biomimetics.”

The new system, described in Nature, is inspired by 

• the bumpy shell of desert beetles, 
• the asymmetric structure of cactus spines and 
• slippery surfaces of pitcher plants. 

The material harnesses the power of these natural systems, plus Slippery Liquid-Infused Porous Surfaces technology (SLIPS) developed in Aizenberg’s lab, to collect and direct the flow of condensed water droplets.

This approach is promising not only for harvesting water but also for industrial heat exchangers.

“Thermal power plants, for example, rely on condensers to quickly convert steam to liquid water,” said Philseok Kim, co-author of the paper and co-founder and vice president of technology at SEAS spin-off SLIPS Technologies, Inc. “This design could help speed up that process and even allow for operation at a higher temperature, significantly improving the overall energy efficiency.”   

The major challenges in harvesting atmospheric water are controlling the size of the droplets, speed in which they form and the direction in which they flow.  

For years, researchers focused on the hybrid chemistry of the beetle’s bumps — a hydrophilic top with hydrophobic surroundings — to explain how the beetle attracted water.  However, Aizenberg and her team took inspiration from a different possibility – that convex bumps themselves also might be able to harvest water.

Time lapse of droplets growing faster on the apex of the bumps compared to a flat region with the same height. (Courtesy of the Aizenberg Lab/Harvard SEAS)

“We experimentally found that the geometry of bumps alone could facilitate condensation,” said Kyoo-Chul Park, a postdoctoral researcher and the first author of the paper.  “By optimizing that bump shape through detailed theoretical modeling and combining it with the asymmetry of cactus spines and the nearly friction-free coatings of pitcher plants, we were able to design a material that can collect and transport a greater volume of water in a short time compared to other surfaces.”

 

Inspired by a cactus spine, asymmetric topography guides the droplet off the bump. (Courtesy of the Aizenberg Lab/Harvard SEAS)

“Without one of those parameters, the whole system would not work synergistically to promote both the growth and accelerated directional transport of even small, fast condensing droplets,” said Park.

“This research is an exciting first step towards developing a passive system that can efficiently collect water and guide it to a reservoir,” said Kim.

This research was supported by the Department of Energy.