Tag Archives: Hendrik Hölscher

More on the blue tarantula noniridescent photonics

Covered in an Oct. 19, 2016 posting here, some new details have been released about noniridescent photonics and blue tarantulas, this time from the Karlsruhe Institute of Technology (KIT) in a Nov. 17, 2016 (?) press release (also on EurekAlert; h/t Nanowerk Nov. 17, 2016 news item) ,

Colors are produced in a variety of ways. The best known colors are pigments. However, the very bright colors of the blue tarantula or peacock feathers do not result from pigments, but from nanostructures that cause the reflected light waves to overlap. This produces extraordinarily dynamic color effects. Scientists from Karlsruhe Institute of Technology (KIT), in cooperation with international colleagues, have now succeeded in replicating nanostructures that generate the same color irrespective of the viewing angle. DOI: 10.1002/adom.201600599

In contrast to pigments, structural colors are non-toxic, more vibrant and durable. In industrial production, however, they have the drawback of being strongly iridescent, which means that the color perceived depends on the viewing angle. An example is the rear side of a CD. Hence, such colors cannot be used for all applications. Bright colors of animals, by contrast, are often independent of the angle of view. Feathers of the kingfisher always appear blue, no matter from which angle we look. The reason lies in the nanostructures: While regular structures are iridescent, amorphous or irregular structures always produce the same color. Yet, industry can only produce regular nanostructures in an economically efficient way.

Radwanul Hasan Siddique, researcher at KIT in collaboration with scientists from USA and Belgium has now discovered that the blue tarantula does not exhibit iridescence in spite of periodic structures on its hairs. First, their study revealed that the hairs are multi-layered, flower-like structure. Then, the researchers analyzed its reflection behavior with the help of computer simulations. In parallel, they built models of these structures using nano-3D printers and optimized the models with the help of the simulations. In the end, they produced a flower-like structure that generates the same color over a viewing angle of 160 degrees. This is the largest viewing angle of any synthetic structural color reached so far.


Flower-shaped nanostructures generate the color of the blue tarantula. (Graphics: Bill Hsiung, University of Akron)

 


The 3D print of the optimized flower structure is only 15 µm in dimension. A human hair is about three times as thick. (Photo: Bill Hsiung, Universtiy of Akron)

Apart from the multi-layered structure and rotational symmetry, it is the hierarchical structure from micro to nano that ensures homogeneous reflection intensity and prevents color changes.

Via the size of the “flower,” the resulting color can be adjusted, which makes this coloring method interesting for industry. “This could be a key first step towards a future where structural colorants replace the toxic pigments currently used in textile, packaging, and cosmetic industries,” says Radwanul Hasan Siddique of KIT’s Institute of Microstructure Technology, who now works at the California Institute of Technology. He considers short-term application in textile industry feasible.


The synthetically generated flower structure inspired by the blue tarantula reflects light in the same color over a viewing angle of 160 degrees. (Graphics: Derek Miller)  

Dr. Hendrik Hölscher thinks that the scalability of nano-3D printing is the biggest challenge on the way towards industrial use. Only few companies in the world are able to produce such prints. In his opinion, however, rapid development in this field will certainly solve this problem in the near future.

Once again, here’s a link to and a citation for the paper,

Tarantula-Inspired Noniridescent Photonics with Long-Range Order by Bor-Kai Hsiung, Radwanul Hasan Siddique, Lijia Jiang, Ying Liu, Yongfeng Lu, Matthew D. Shawkey, and Todd A. Blackledge. Advanced Materials DOI: 10.1002/adom.201600599 Version of Record online: 11 OCT 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The paper is behind a paywall. You can see the original Oct. 19, 2016 posting for my comments and some excerpts from the paper.

Oil-absorbing hairy fern leaves lead to ‘nanofur’ for oil spill cleanups

German researchers have developed a biomimetic material branded as ‘nanofur’ for oil spill cleanups, according to an Aug. 23, 2016 news item on Nanowerk (Note: A link has been removed),

Some water ferns can absorb large volumes of oil within a short time, because their leaves are strongly water-repellent and, at the same time, highly oil-absorbing. Researchers of Karlsruhe Institute of Technology, together with colleagues of Bonn University, have found that the oil-binding capacity of the water plant results from the hairy microstructure of its leaves (Bioinspiration & Biomimetics, “Microstructures of superhydrophobic plant leaves – inspiration for efficient oil spill cleanup materials”). It is now used as a model to further develop the new Nanofur material for the environmentally friendly cleanup of oil spills.

An Aug.(?) 23 (?), 2016 Karlsruhe Institute of Technology (KIT) press release on EurekAlert, which originated the news item, explains the interest in improving technology for oil spill cleanups and provides insight into this  innovation,

Damaged pipelines, oil tanker disasters, and accidents on oil drilling and production platforms may result in pollutions [sic] of water with crude or mineral oil. Conventional methods to clean up the oil spill are associated with specific drawbacks. Oil combustion or the use of chemical substances to accelerate oil decomposition cause secondary environmental pollution. Many natural materials to take up the oil, such as sawdust or plant fibers, are hardly effective, because they also absorb large amounts of water. On their search for an environmentally friendly alternative to clean up oil spills, the researchers compared various species of aquatic ferns. “We already knew that the leaves of these plants repel water, but for the first time now, we have studied their capacity to absorb oil,” Claudia Zeiger says. She conducted the project at KIT’s Institute of Microstructure Technology.

Damaged pipelines, oil tanker disasters, and accidents on oil drilling and production platforms may result in pollutions of water with crude or mineral oil. Conventional methods to clean up the oil spill are associated with specific drawbacks. Oil combustion or the use of chemical substances to accelerate oil decomposition cause secondary environmental pollution. Many natural materials to take up the oil, such as sawdust or plant fibers, are hardly effective, because they also absorb large amounts of water. On their search for an environmentally friendly alternative to clean up oil spills, the researchers compared various species of aquatic ferns. “We already knew that the leaves of these plants repel water, but for the first time now, we have studied their capacity to absorb oil,” Claudia Zeiger says. She conducted the project at KIT’s Institute of Microstructure Technology.

Aquatic ferns originally growing in tropical and subtropical regions can now also be found in parts of Europe. As they reproduce strongly, they are often considered weed. However, they have a considerable potential as low-cost, rapid, and environmentally friendly oil absorbers, which is obvious from a short video (see below). ”The plants might be used in lakes to absorb accidental oil spills,” Zeiger says. After less than 30 seconds, the leaves reach maximum absorption and can be skimmed off together with the absorbed oil. The water plant named salvinia has trichomes on the leaf surface – hairy extensions of 0.3 to 2.5 mm in length. Comparison of different salvinia species revealed that leaves with the longest hairs did not absorb the largest amounts of oil. “Oil-absorbing capacity is determined by the shape of the hair ends,” Zeiger emphasizes. The largest quantity of oil was absorbed by leaves of the water fern salvinia molesta, whose hair ends are shaped like an eggbeater.

Based on this new knowledge on the relationship between surface structure of leaves and their oil-absorbing capacity, the researchers improved the ‘Nanofur’ material developed at their institute. This plastic nanofur mimics the water-repellent and oil-absorbing effect of salvinia to separate oil and water. “We study nanostructures and microstructures in nature for potential technical developments,” says Hendrik Hölscher, Head of the Biomimetic Surfaces Group of the Institute of Microstructure Technology of KIT. He points out that different properties of plants made of the same material frequently result from differences of their finest structures.

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

Microstructures of superhydrophobic plant leaves – inspiration for efficient oil spill cleanup materials by Claudia Zeiger, Isabelle C Rodrigues da Silva, Matthias Mail, Maryna N Kavalenka, Wilhelm Barthlott, and Hendrik Hölscher. Bioinspiration & Biomimetics, Volume 11, Number 5 DOI: http://dx.doi.org/10.1088/1748-3190/11/5/056003

Published 16 August 2016, © 2016 IOP Publishing Ltd

This article appears to be open access.

There is also a video demonstration of the material,

Enjoy!

Glasswing butterflies teach us about reflection

Contrary to other transparent surfaces, the wings of the glasswing butterfly (Greta Oto) hardly reflect any light. Lenses or displays of mobiles might profit from the investigation of this phenomenon. (Photo: Radwanul Hasan Siddique, KIT)

Contrary to other transparent surfaces, the wings of the glasswing butterfly (Greta Oto) hardly reflect any light. Lenses or displays of mobiles might profit from the investigation of this phenomenon. (Photo: Radwanul Hasan Siddique, KIT)

I wouldn’t have really believed. Other than glass, I’ve never seen anything in nature that’s as transparent and distortion-free as this butterfly’s wings.

An April 22, 2015 news item on ScienceDaily provides more information about the butterfly,

The effect is known from the smart phone: Sun is reflected by the display and hardly anything can be seen. In contrast to this, the glasswing butterfly hardly reflects any light in spite of its transparent wings. As a result, it is difficult for predatory birds to track the butterfly during the flight. Researchers of KIT under the direction of Hendrik Hölscher found that irregular nanostructures on the surface of the butterfly wing cause the low reflection. In theoretical experiments, they succeeded in reproducing the effect that opens up fascinating application options, e.g. for displays of mobile phones or laptops.

An April 22, 2015 Karlsruhe Institute of Technology (KIT) press release (also on EurekAlert), which originated the news item, explains the scientific interest,

Transparent materials such as glass, always reflect part of the incident light. Some animals with transparent surfaces, such as the moth with its eyes, succeed in keeping the reflections small, but only when the view angle is vertical to the surface. The wings of the glasswing butterfly that lives mainly in Central America, however, also have a very low reflection when looking onto them under higher angles. Depending on the view angle, specular reflection varies between two and five percent. For comparison: As a function of the view angle, a flat glass plane reflects between eight and 100 percent, i.e. reflection exceeds that of the butterfly wing by several factors. Interestingly, the butterfly wing does not only exhibit a low reflection of the light spectrum visible to humans, but also suppresses the infrared and ultraviolet radiation that can be perceived by animals. This is important to the survival of the butterfly.

For research into this so far unstudied phenomenon, the scientists examined glasswings by scanning electron microscopy. Earlier studies revealed that regular pillar-like nanostructures are responsible for the low reflections of other animals. The scientists now also found nanopillars on the butterfly wings. In contrast to previous findings, however, they are arranged irregularly and feature a random height. Typical height of the pillars varies between 400 and 600 nanometers, the distance of the pillars ranges between 100 and 140 nanometers. This corresponds to about one thousandth of a human hair.

In simulations, the researchers mathematically modeled this irregularity of the nanopillars in height and arrangement. They found that the calculated reflected amount of light exactly corresponds to the observed amount at variable view angles. In this way, they proved that the low reflection at variable view angles is caused by this irregularity of the nanopillars. Hölscher’s doctoral student Radwanul Hasan Siddique, who discovered this effect, considers the glasswing butterfly a fascinating animal: “Not only optically with its transparent wings, but also scientifically. In contrast to other natural phenomena, where regularity is of top priority, the glasswing butterfly uses an apparent chaos to reach effects that are also fascinating for us humans.”

The findings open up a range of applications wherever low-reflection surfaces are needed, for lenses or displays of mobile phones, for instance. Apart from theoretical studies of the phenomenon, the infrastructure of the Institute of Microstructure Technology also allows for practical implementation. First application tests are in the conception phase at the moment. Prototype experiments, however, already revealed that this type of surface coating also has a water-repellent and self-cleaning effect.

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

The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly by Radwanul Hasan Siddique, Guillaume Gomard, & Hendrik Hölscher. Nature Communications 6, Article number: 6909 doi:10.1038/ncomms7909 Published 22 April 2015

The paper is behind a paywall but there is a free preview via ReadCube Access.