Tag Archives: superhydrophilic

Do Tenebrionind beetles collect dew or condensation—a water issue at the nanoscale

Up until now, the research I’ve stumbled across about Tenebrionind beetles and their water-collecting ways has been from the US but this latest work comes from a France/Spain,/UK collaboration which focused on a specific question, exactly where do these beetles harvest their water from? A Dec. 8, 2014 news item on Nanotechnology Now describes this latest research,

Understanding how a desert beetle harvests water from dew could improve drinking water collection in dew condensers

Insects are full of marvels – and this is certainly the case with a beetle from the Tenebrionind family, found in the extreme conditions of the Namib desert. Now, a team of scientists has demonstrated that such insects can collect dew on their backs – and not just fog as previously thought. This is made possible by the wax nanostructure on the surface of the beetle’s elytra. … They bring us a step closer to harvesting dew to make drinking water from the humidity in the air. This, the team hopes, can be done by improving the water yield of man-made dew condensers that mimick the nanostructure on the beetle’s back.

A Dec. 8, 2014  Springer press release (also on EurekAlert), which originated the news item, describes how this research adds to the body of knowledge about the ability to harvest water from the air,

It was not clear from previous studies whether water harvested by such beetles came from dew droplets, in addition to fog. Whereas fog is made of ready-made microdroplets floating in the air, dew appears following the cooling of a substrate below air temperature. This then turns the humidity of air into tiny droplets of water because more energy – as can be measured through infrared emissions – is sent to the atmosphere than received by it. The cooling capability is ideal, they demonstrated, because the insect’s back demonstrates near-perfect infrared emissivity.

Guadarrama-Cetina [José Guadarrama-Cetina] and colleagues also performed an image analysis of dew drops forming on the insect’s back on the surface of the elytra, which appears as a series of bumps and valleys. Dew primarily forms in the valleys endowed with a hexagonal microstructure, they found, unlike the smooth surface of the bumps. This explains how drops can slide to the insect’s mouth when they reach a critical size.

Here’s a link to and a citation for the paper,

Dew condensation on desert beetle skin by J.M. Guadarrama-Cetina, A. Mongruel, M.-G. Medici, E. Baquero, A.R. Parker, I. Milimouk-Melnytchuk, W. González-Viñas, and D. Beysens. Eur. Phys. J. E (European Physics Journal E 2014) 37: 109, DOI 10.1140/epje/i2014-14109-y

This paper is currently (Dec. 8, 2014) open access. I do not know if this will be permanent or if access rights will change over time.

My previous postings on the topic of water and beetles have focused on US research of the Stenocara beetle (aka Namib desert beetle) which appears to be a member of the Tenebrionind family of beetles mentioned in this latest research.

The European researchers have provided an image of the beetle they were examining,

A preserved specimen of the Tenebrionind beetle (Physasterna cribripes) was used for this study, displaying the insect’s mechanisms of dew harvesting. © J.M. Guadarrama-Cetina et al.

A preserved specimen of the Tenebrionind beetle (Physasterna cribripes) was used for this study, displaying the insect’s mechanisms of dew harvesting. © J.M. Guadarrama-Cetina et al.

As for my other pieces on this topic, there’s a July 29, 2014 post, a June 18, 2014 post, and a Nov. 26, 2012 post.

NBD Nano startup company and the Namib desert beetle

In 2001, Andrew Parker and Chris Lawrence published an article in Nature magazine about work which has inspired a US startup company in 2012 to develop a water bottle that fills itself up with water by drawing moisture from the air. Parker’s and Lawrence’s article was titled Water capture by a desert beetle. Here’s the abstract (over 10 years later the article is still behind a paywall),

Some beetles in the Namib Desert collect drinking water from fog-laden wind on their backs1. We show here that these large droplets form by virtue of the insect’s bumpy surface, which consists of alternating hydrophobic, wax-coated and hydrophilic, non-waxy regions. The design of this fog-collecting structure can be reproduced cheaply on a commercial scale and may find application in water-trapping tent and building coverings, for example, or in water condensers and engines.

Some five years later, there was a June 15, 2006 news item on phys.org about the development of a new material based on the Namib desert beetle,

When that fog rolls in, the Namib Desert beetle is ready with a moisture-collection system exquisitely adapted to its desert habitat. Inspired by this dime-sized beetle, MIT [Massachusetts Institute of Technology] researchers have produced a new material that can capture and control tiny amounts of water.

The material combines a superhydrophobic (water-repelling) surface with superhydrophilic (water-attracting) bumps that trap water droplets and control water flow. The work was published in the online version of Nano Letters on Tuesday, May 2 [2006] {behind a paywall}.

Potential applications for the new material include harvesting water, making a lab on a chip (for diagnostics and DNA screening) and creating microfluidic devices and cooling devices, according to lead researchers Robert Cohen, the St. Laurent Professor of Chemical Engineering, and Michael Rubner, the TDK Professor of Polymer Materials Science and Engineering.

The MIT June 14, 2006 news release by Anne Trafton, which originated the news item about the new material, indicates there was some military interest,

The U.S. military has also expressed interest in using the material as a self-decontaminating surface that could channel and collect harmful substances.

The researchers got their inspiration after reading a 2001 article in Nature describing the Namib Desert beetle’s moisture-collection strategy. Scientists had already learned to copy the water-repellent lotus leaf, and the desert beetle shell seemed like another good candidate for “bio-mimicry.”

When fog blows horizontally across the surface of the beetle’s back, tiny water droplets, 15 to 20 microns, or millionths of a meter, in diameter, start to accumulate on top of bumps on its back.

The bumps, which attract water, are surrounded by waxy water-repelling channels. “That allows small amounts of moisture in the air to start to collect on the tops of the hydrophilic bumps, and it grows into bigger and bigger droplets,” Rubner said. “When it gets large, it overcomes the pinning force that holds it and rolls down into the beetle’s mouth for a fresh drink of water.”

To create a material with the same abilities, the researchers manipulated two characteristics — roughness and nanoporosity (spongelike capability on a nanometer, or billionths of a meter, scale).

By repeatedly dipping glass or plastic substrates into solutions of charged polymer chains dissolved in water, the researchers can control the surface texture of the material. Each time the substrate is dipped into solution, another layer of charged polymer coats the surface, adding texture and making the material more porous. Silica nanoparticles are then added to create an even rougher texture that helps trap water droplets.

The material is then coated with a Teflon-like substance, making it superhydrophobic. Once that water-repellent layer is laid down, layers of charged polymers and nanoparticles can be added in certain areas, using a properly formulated water/alcohol solvent mixture, thereby creating a superhydrophilic pattern. The researchers can manipulate the technique to create any kind of pattern they want.

The research is funded by the Defense Advanced Research Projects Agency and the National Science Foundation.

I’m not sure what happened with the military interest or the group working out of MIT in 2006 but on Nov. 23, 2012, BBC News online featured an article about a US startup company, NBD Nano, which aims to bring a self-filling water bottle based on Namib desert beetle to market,

NBD Nano, which consists of four recent university graduates and was formed in May, looked at the Namib Desert beetle that lives in a region that gets about half an inch of rainfall per year.

Using a similar approach, the firm wants to cover the surface of a bottle with hydrophilic (water-attracting) and hydrophobic (water-repellent) materials.

The work is still in its early stages, but it is the latest example of researchers looking at nature to find inspiration for sustainable technology.

“It was important to apply [biomimicry] to our design and we have developed a proof of concept and [are] currently creating our first fully-functional prototype,” Miguel Galvez, a co-founder, told the BBC.

“We think our initial prototype will collect anywhere from half a litre of water to three litres per hour, depending on local environments.”

According to the Nov. 25, 2012 article by Nancy Owano for phys.org, the company is at the prototype stage now,

NBD Nano plans to enter the worldwide marketplace between 2014 and 2015.

You can find out more about NBD Nano here.