Tag Archives: optical properties

Tough colour and the flower beetle

The flower beetle Torynorrhina flammea. [downloaded from https://www.nanowerk.com/nanotechnology-news2/newsid=58269.php]

That is one gorgeous beetle and a June 17, 2021 news item on Nanowerk reveals that it features in a structural colour story (i.e, how structures rather than pigments create colour),

The unique mechanical and optical properties found in the exoskeleton of a humble Asian beetle has the potential to offer a fascinating new insight into how to develop new, effective bio-inspired technologies.

Pioneering new research by a team of international scientists, including Professor Pete Vukusic from the University of Exeter, has revealed a distinctive, and previously unknown property within the carapace of the flower beetle – a member of the scarab beetle family.

The study showed that the beetle has small micropillars within the carapace – or the upper section of the exoskeleton – that give the insect both strength and flexibility to withstand damage very effectively.

Crucially, these micropillars are incorporated into highly regular layering in the exoskeleton that concurrently give the beetle an intensely bright metallic colour appearance.

A June 18, 2021 University of Exeter press release (also on EurekAlert but published June 17, 2021), delves further into the researchers’ new insights,

For this new study, the scientists used sophisticated modelling techniques to determine which of the two functions – very high mechanical strength or conspicuously bright colour – were more important to the survival of the beetle.

They found that although these micropillars do create a highly enhanced toughness of the beetle shell, they were most beneficial for optimising the scattering of coloured light that generates its conspicuous appearance.

The research is published this week in the leading journal, Proceedings of the National Academy of Sciences, PNAS.

Professor Vukusic, one of three leads of the research along with Professor Li at Virginia Tech and Professor Kolle at MIT [Massachusetts Institute of Technology], said: “The astonishing insights generated by this research have only been possible through close collaborative work between Virginia Tech, MIT, Harvard and Exeter, in labs that trailblaze the fields of materials, mechanics and optics. Our follow-up venture to make use of these bio-inspired principles will be an even more exciting journey.”.

The seeds of the pioneering research were sown more than 16 years ago as part of a short project created by Professor Vukusic in the Exeter undergraduate Physics labs. Those early tests and measurements, made by enthusiastic undergraduate students, revealed the possibility of intriguing multifunctionality.

The original students examined the form and structure of beetles’ carapce to try to understand the simple origin of their colour. They noticed for the first time, however, the presence of strength-inducing micropillars.

Professor Vukusic ultimately carried these initial findings to collaborators Professor Ling Li at Virginia Tech and Professor Mathias Kolle at Harvard and then MIT who specialise in the materials sciences and applied optics. Using much more sophisticated measurement and modelling techniques, the combined research team were also to confirm the unique role played by the micropillars in enhancing the beetles’ strength and toughness without compromising its intense metallic colour.

The results from the study could also help inspire a new generation of bio-inspired materials, as well as the more traditional evolutionary research.

By understanding which of the functions provides the greater benefit to these beetles, scientists can develop new techniques to replicate and reproduce the exoskeleton structure, while ensuring that it has brilliant colour appearance with highly effective strength and toughness.

Professor Vukusic added: “Such natural systems as these never fail to impress with the way in which they perform, be it optical, mechanical or in another area of function. The way in which their optical or mechanical properties appear highly tolerant of all manner of imperfections too, continues to offer lessons to us about scientific and technological avenues we absolutely should explore. There is exciting science ahead of us on this journey.”

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

Microstructural design for mechanical–optical multifunctionality in the exoskeleton of the flower beetle Torynorrhina flammea by Zian Jia, Matheus C. Fernandes, Zhifei Deng, Ting Yang, Qiuting Zhang, Alfie Lethbridge, Jie Yin, Jae-Hwang Lee, Lin Han, James C. Weaver, Katia Bertoldi, Joanna Aizenberg, Mathias Kolle, Pete Vukusic, and Ling Li. PNAS June 22, 2021 118 (25) e2101017118; DOI: https://doi.org/10.1073/pnas.2101017118

This paper is behind a paywall.

How tarantulas get blue

Cobalt Blue Tarantula [downloaded from http://www.tarantulaguide.com/tarantula-pictures/cobalt-blue-tarantula-4/]

Cobalt Blue Tarantula [downloaded from http://www.tarantulaguide.com/tarantula-pictures/cobalt-blue-tarantula-4/]

That’s a stunning shade of blue on the tarantula and now scientists can explain why these and other ‘spiders’ are sometimes blue, from a Nov. 30, 2015 news item on ScienceDaily,

Scientists recently discovered that tiny, multilayer nanostructures inside a tarantula’s hair are responsible for its vibrant color. The science behind how these hair-raising spiders developed their blue hue may lead to new ways to improve computer or TV screens using biomimicry.

A Nov. 30, 2015 University of California at San Diego news release by Annie Reisewitz, which originated the news item, explains more,

Researchers from Scripps Institution of Oceanography at UC San Diego and University of Akron found that many species of tarantulas have independently evolved the ability to grow blue hair using nanostructures in their exoskeletons, rather than pigments. The study, published in the Nov. 27 issue of Science Advances, is the first to show that individual species evolved separately to make the same shade of a non-iridescent color, one that doesn’t change when viewed at different angles.

Since tarantulas’ blue color is not iridescent, the researchers suggest that the same process can be applied to make pigment replacements that never fade and help reduce glare on wide-angle viewing systems in phones, televisions, and other devices.

“There is strikingly little variety in the shade of blue produced by different species of tarantulas,” said Dimitri Deheyn, a Scripps Oceanography researcher studying marine and terrestrial biomimicry and coauthor of the study. “We see that different types of nanostructures evolved to produce the same ‘blue’ across distant branches of the tarantula family tree in a way that uniquely illustrates natural selection through convergent evolution.”

Unlike butterflies and birds that use nanostructures to produce vibrant colors to attract the attention of females during display courtship, tarantulas have poor vision and likely evolved this trait for a different reason. While the researchers still don’t understand the benefits tarantulas receive from being blue, they are now investigating how to reproduce the tarantula nanostructures in the laboratory.

The tarantula study is just one example of the biomimicry research being conducted in the Deheyn lab at Scripps Oceanography. In a cover article in the Nov. 10 of Chemistry of Materials, Deheyn and colleagues published new findings on the nanostructure of ragweed pollen, which shows interesting optical properties and has possible biomimicry applications. By transforming the pollen into a magnetic material with a specialized coating to give it more or less reflectance, the particle could adhere in a similar way that pollen does in nature while being able to adjust its visibility. The researchers suggest this design could be applied to create a new type of tagging or tracking technology.

Using a high-powered microscope, known as a hyperspectral imaging system, Deheyn is able to map a species’ color field pixel by pixel, which correlates to the shape and geometry of the nanostructures and gives them their unique color.

“This unique technology allows us to associate structure with optical property,” said Deheyn. “Our inspiration is to learn about how nature evolves unique traits that we could mimic to benefit future technologies.”

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

Blue reflectance in tarantulas is evolutionarily conserved despite nanostructural diversity by Bor-Kai Hsiung, Dimitri D. Deheyn, Matthew D. Shawkey, and Todd A. Blackledge. Science Advances  27 Nov 2015: Vol. 1, no. 10, e1500709 DOI: 10.1126/sciadv.1500709

This paper appears to be open access.

Solid gold smoke?

Aerogels seem to enchant even scientists who sometimes call it ‘solid smoke’ (my Aug. 20, 2012 posting). This latest aerogel is made of gold according to a Nov. 25, 2015 news item on Nanowerk,

 A nugget of real 20 carats gold, so light that it does not sink in a cappuccino, floating instead on the milk foam – what sounds unbelievable has actually been accomplished by researchers from ETH Zurich. Scientists led by Raffaele Mezzenga, Professor of Food and Soft Materials, have produced a new kind of foam out of gold, a three-dimensional mesh of gold that consists mostly of pores. It is the lightest gold nugget ever created. “The so-called aerogel is a thousand times lighter than conventional gold alloys. It is lighter than water and almost as light as air,” says Mezzenga.

A Nov. 25, 2015 ETH Zurich press release (also on EurekAlert), which originated the news item, provides more information about the ‘gold smoke’,

The new gold form can hardly be differentiated from conventional gold with the naked eye – the aerogel even has a metallic shine. But in contrast to its conventional form, it is soft and malleable by hand. It consists of 98 parts air and only two parts of solid material. Of this solid material, more than four-fifths are gold and less than one-fifth is milk protein fibrils. This corresponds to around 20 carat gold.

Here’s what it looks like,

Caption: Even when it seems unbelievable: these are genuine photographs, in which nothing has been faked. E.g. the 20 carats gold foam is lighter than milk foam. Credit: Gustav Nyström and Raffaele Mezzenga / (copyright) ETH Zurich

Caption: Even when it seems unbelievable: these are genuine photographs, in which nothing has been faked. E.g. the 20 carats gold foam is lighter than milk foam.
Credit: Gustav Nyström and Raffaele Mezzenga / (copyright) ETH Zurich

The press release provides more technical details,

The scientists created the porous material by first heating milk proteins to produce nanometre-fine protein fibres, so-called amyloid fibrils, which they then placed in a solution of gold salt. The protein fibres interlaced themselves into a basic structure along which the gold simultaneously crystallised into small particles. This resulted in a gel-like gold fibre network.

“One of the big challenges was how to dry this fine network without destroying it,” explains Gustav Nyström, postdoc in Mezzenga’s group and first author of the corresponding study in the journal Advanced Materials. As air drying could damage the fine gold structure, the scientists opted for a gentle and laborious drying process using carbon dioxide. They did so in an interdisciplinary effort assisted by researchers in the group of Marco Mazzotti, Professor of Process Engineering.

Dark-red gold

The method chosen, in which the gold particles are crystallised directly during manufacture of the aerogel protein structure (and not, for example, added to an existing scaffold) is new. The method’s biggest advantage is that it makes it easy to obtain a homogeneous gold aerogel, perfectly mimicking gold alloys.

The manufacturing technique also offers scientists numerous possibilities to deliberately influence the properties of gold in a simple manner. ” The optical properties of gold depend strongly on the size and shape of the gold particles,” says Nyström. “Therefore we can even change the colour of the material. When we change the reaction conditions in order that the gold doesn’t crystallise into microparticles but rather smaller nanoparticles, it results in a dark-red gold.” By this means, the scientists can influence not only the colour, but also other optical properties such as absorption and reflection.

The new material could be used in many of the applications where gold is currently being used, says Mezzenga. The substance’s properties, including its lighter weight, smaller material requirement and porous structure, have their advantages. Applications in watches and jewellery are only one possibility. Another application demonstrated by the scientists is chemical catalysis: since the highly porous material has a huge surface, chemical reactions that depend on the presence of gold can be run in a very efficient manner. The material could also be used in applications where light is absorbed or reflected. Finally, the scientists have also shown how it becomes possible to manufacture pressure sensors with it. “At normal atmospheric pressure the individual gold particles in the material do not touch, and the gold aerogel does not conduct electricity,” explains Mezzenga. “But when the pressure is increased, the material gets compressed and the particles begin to touch, making the material conductive.”

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

Amyloid Templated Gold Aerogels by Gustav Nyström, Maria P. Fernandez-Ronco, Sreenath Bolisetty, Marco Mazzotti, Raffaele Mezzenaga. Advanced Materials DOI: 10.1002/adma.201503465 First published: 23 November 2015

This paper is behind a paywall.

Qualitative and quantitative understanding of nanostructures by University of BC researchers

It’s not the sexiest research (no nanobots, no self-cleaning windows, no textiles with colours never seen before on fabrics, no heating up a tumour to destroy it, etc.)  I’ve come across but developing a model that predicts a nanostructure’s optical properties is likely to prove valuable. According to the University of British Columbia Chemistry Department researchers the models could be useful with the “design of tailored nano-structures, and be of utility in a wide range of fields, including the remote sensing of atmospheric pollutants and the study of cosmic dust formation.”

From the March 24, 2011 news item on Nanowerk,

Now research published this week by UBC chemists indicates that the optical properties of more complex non-conducting nano-structures can be predicted based on an understanding of the simple nano-objects that make them up. Those optical properties in turn give researchers and engineers an understanding of the particle’s structure.

“Engineering complex nano-structures with particular infrared responses typically involves hugely complex calculations and is a bit hit and miss,” says Thomas Preston, a researcher with the UBC Department of Chemistry.

“Our solution is a relatively simple model that could help guide us in more efficiently engineering nano-materials with the properties we want, and help us understand the properties of these small particles that play an important role in so many processes.”

The findings were published this week in the Proceedings of the National Academy of Sciences (“Vibron and phonon hybridization in dielectric nanostructures”).

“For example, the properties of a more complex particle made up of a cavity and a core structure can be understood as a hybrid of the individual pieces that make it up,” says UBC Professor Ruth Signorell, an expert on the characterization of molecular nano-particles and aerosols and co-author of the study.

The experiment also tested the model against CO2 aerosols with a cubic shape, which play a role in cloud formation on Mars.

The paper, Vibron and phonon hybridization in dielectric nanostructures, is behind a Proceedings of the National Academy of Sciences paywall but an abstract is available here.