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.

Freaky Flowers - Echinopsis Cacti in Bloom

A montage of a dozen types of Echinopsis cactus flowers blooming. And wilting. And just generally showing off their mind-blowing colors. My favorite cactus flowerings from the 2014 blooming season.

Echinopsis cactus flowers bloom overnight and the flowers last for only a day. Actually, the flowers are at their peak beauty for an hour or two at the most. That's what turned me from a cactus enthusiast into a cactus photographer ... the desire to try to preserve some aspect of their freaky beauty. Prior to becoming an Echinopsis addict a few years back, I had never owned a DSLR or image/video editing software.

The cacti shown in this video come from my collection. The evening when it looks like a plant's flowers are about to bloom, I bring it indoors to image. Most of the clips in this montage show approximately 8 hours of change as the flowers open and bloom. A little more than halfway through the montage, there's a series of three clips showing different views of a 24-hour period in the life of a yellow-flowered 'Daydream' plant. Six flowers that opened the night before I started filming wilt to nothingness and another 4 flowers grow dramatically and then open. This series of 'Daydream' clips is followed by another three showing other types of flowers wilting. These additional wilting clips are also taken over a daylong period.

The question I'm asked most often about my cactus flower still images and timelapses is whether I've "Photoshopped" them, that is, have I used editing software to juice things up and create the flowers' intense colors. I do, of course, use Photoshop and Lightroom and other editing software. But not in the way most suspect. Rather than using these tools to overstate reality, I actually use them to reduce the intensity of the colors my camera captures. I have reduced the color saturation in every timelapse clip in this video by a minimum of 10% and some ('Yes', 'Cabaret' and 'Antimatter') by 30% or more in order to have something that wasn't just completely blown out. 

I hope you enjoy "Freaky Flowers" and invite you to visit www.echinopsisfreak.com where you'll learn more than you ever wanted to know about these cacti and also be able to reach me via a contact page should you wish. 

The 2015 blooming season is just about to start now that April approaches and I hope to be posting new timelapses soon here at Vimeo.

ORIGINAL: Echinopsis Freak

Cactus-inspired material cleans oily water

ORIGINAL: BBC
By Simon Redfern Reporter, BBC News
6 August 2013

Oil spills may be cleaned using a method inspired by cactus needles

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Arrays of tiny copper spikes can clean oil from water, mimicking the way cacti pull water out of desert air.

Chinese researchers had noticed that cone-shaped cactus spines harvest water from air pushing it to their base.

Copying Nature's design, they used conical copper needles to separate tiny oil drops from dirty water - a problem existing methods struggle with.

The scientists, who are based in Beijing, have reported their results in the journal Nature Communications.
 
“Nature has perfected methods over the years and this group has done a great job at figuring out how to put it all together” Stephen Michielsen Professor, North Carolina State University

The discovery points the way to a new method for addressing environmental problems like oil spill clean up, with the artificial spines capturing microscopic droplets of oil underwater, continuously transporting them to the base of the sheet of spikes.

Last year, researchers from Beijing reported the discovery that the conical needles of the "bunny ear" cactus, Optunia microdasys, can collect water from the air.

Droplets of water coalesce on its barbed spines and are then driven to the spine base by the interaction between the shape of the spine and the surface tension of the water droplet.

They now report that synthetic spines are capable of separating and collecting oil droplets out of water in just the same way, and have made a synthetic "cactus skin" of needles that do exactly that.

While oil and water don't mix, if very small droplets of oil co-mingle with water it becomes almost impossible to separate the droplets out of the water again - an example is homogenised milk, in which tiny fat droplets stay suspended in the milk forever.

Describing their method, Lei Jiang, leader of the research project, said: "We fabricated needle arrays. Each conical needle in the array is a little oil collection device. The arrays can collect micron-sized oil droplets from water continuously and effectively." Microscopic bed of nails

The synthetic needles are half a millimetre long, and will remove tiny micron-sized droplets of oil from water, which are very difficult to separate out by any other method. In tests they found that hexagonal arrays of these needles could separate around 99% of oil mixed with water.

Arrays of needles 0.5 mm tall can harvest oil from water

The researchers have constructed conical needles made of copper and of a silicone polymer and find that the affinity of the material surface for oil, together with the shape of the cone are crucial in the operation of the device, but that rougher cones are more efficient at harvesting oil from water.

"This excellent piece of work provides a perfect example of first describing an interesting biological system and then taking it one step further by solving an engineering problem." Professor Joanna Aizenberg of Harvard University told the BBC. "It shows not only how we can learn from Nature but also how to apply that knowledge in bio-inspired design.

"It is a beautiful experiment, and seems very effective showing almost complete separation of oil and water. Next, it will require scaling up and testing in field experiments."

The phenomenon relies on the fact that the radius of a cone surface is very small near the tip, and larger further from the tip towards the base. This causes a pressure difference for a droplet at the tip compared to near the base forcing the liquid to move to the wider part of the cone. As a droplet moves along it captures any others on the way, coalescing at the cone's base.

Different types of oil-water mixtures were tested, including vegetable oil, gasoline, and organic solvents mixed with water, and all were successfully separated in the same process.

Structured surfaces can separate mixtures (left) to near pure oil (centre) and water (right)

Copying designs from Nature, or biomimicry, is a growing area of materials technology, and such materials are termed biomimetic.

Professor Stephen Michielsen from North Carolina State University spoke to the BBC and said of the Beijing group: "Their main research area is trying to mimic Nature. In the past they have looked at spiders' webs and at cacti, and now they are using the same concepts to gather tiny tiny oil droplets from water.

"Their method should also work to remove really tiny oil drops from air, which occur when oil gets aerosolised in compressed air. This should be a more efficient method than filters.

"They are very good at observing what Nature does and mimicking it - Nature has perfected methods over the years and this group has done a great job at figuring out how to put it all together."

Previous examples of biomimetic inventions include Velcro fasteners (copying plant burrs that get stuck onto animal fur), the friction-reducing sharkskin swimsuits used at the Beijing Olympics, and artificial photosynthesis employed by some of the latest solar cells.