Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Understanding nature's most striking colors

16.09.2015

Researchers show how natural materials like plant cellulose can self-assemble into surfaces with stunning optical properties -- including shiny iridescence and colors that change depending on the humidity

The tulip called Queen of the Night has a fitting name. Its petals are a lush, deep purple that verges on black. An iridescent shimmer dances on top of the nighttime hues, almost like moonlight glittering off regal jewels.


The Queen of the Night tulip displays an iridescent shimmer caused by microscopic ridges on its petals that diffract light.

Credit: S. Vignolini/


A schematic of cellulose fibers in the cholesteric phase. The fibers in a single layer align in a single direction. Travelling through multiple layers, the axis of orientation of the fibers spins in a circle.

Credit: Abigail Malate

Certain rainforest plants in Malaysian demonstrate an even more striking color feature: Their iridescent blue leaves turn green when dunked in water.

Both the tulip's rainbow sparkle and the Malaysian plants' color change are examples of structural color -- an optical effect that is produced by a physical structure, instead of a chemical pigment.

Now researchers have shown how plant cellulose can self-assemble into wrinkled surfaces that give rise to effects like iridescence and color change. Their findings provide a foundation to understand structural color in nature, as well as yield insights that could guide the design of devices like optical humidity sensors. The researchers describe their results in a paper in The Journal of Chemical Physics, from AIP Publishing

Starting with Twisting Cellulose

Cellulose is one of the most abundant organic materials on Earth. It forms a key part of the cell wall of green plants, where the cellulose fibers are found in layers. The fibers in a single layer tend to align in a single direction. However, when you move up or down a layer the axis of orientation of the fibers can shift. If you imagined an arrow pointing in the direction of the fiber alignment, it would often spin in a circle as you moved through the layers of cellulose. This twisting pattern is called a cholesteric phase, because it was first observed while studying cholesterol molecules.

Scientists think that cellulose twists mainly to provide strength. "The fibers reinforce in the direction they are oriented," said Alejandro Rey, a chemical engineer at McGill University in Montreal, Canada. "When the orientation rotates you get multi-directional stiffness."

Rey and his colleagues, however, weren't primarily interested in cellulose's mechanical properties. Instead, they wondered if the twisting structure could produce striking optical effects, as seen in plants like iridescent tulips.

The team constructed a computational model to examine the behavior of cholesteric phase cellulose. In the model, the axis of twisting runs parallel to the surface of the cellulose. The researchers found that subsurface helices naturally caused the surface to wrinkle. The tiny ridges had a height range in the nanoscale and were spaced apart on the order of microns.

The pattern of parallel ridges resembled the microscopic pattern on the petals of the Queen of the Night tulip. The ridges split white light into its many colored components and create an iridescent sheen -- a process called diffraction. The effect can also be observed when light hits the microscopic grooves in a CD.

The researchers also experimented with how the amount of water in the cellulose layers affected the optical properties. More water made the layers twist less tightly, which in turn made the ridges farther apart. How tightly the cellulose helices twist is called the pitch. The team found that a surface with spatially varying pitch (in which some areas were more hydrated than others) was less iridescent and reflected a longer primary wavelength of light than surfaces with a constant pitch. The wavelength shift from around 460 nm (visible blue light) to around 520 nm (visible green light) could explain some plants' color changing properties, Rey said.

Insights into Nature and Inspiration for New Technologies

Although proving that diffractive surfaces in nature form in the same way will require further work, the model does offer a good foundation to further explore structural color, the researchers said. They imagine the model could also guide the design of new optical devices, for example sensors that change color to indicate a change in humidity.

"The results show the optics [of cholesteric cellulose] are just as exciting as the mechanical properties," Rey said. He said scientists tend to think of the structures as biological armor, because of their reinforcing properties. "We've shown this armor can also have striking colors," he said.

###

The article, "Tunable Nano-wrinkling of Chiral Surfaces: Structure and Diffraction Optics" is authored by P. Rofouie, D. Pasini and A.D. Rey. It will be published in the Journal of Chemical Physics on September 15, 2015 (DOI: 10.1063/1.4929337). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/jcp/143/11/10.1063/1.4929337

The authors of this paper are affiliated with McGill University.

ABOUT THE JOURNAL

The Journal of Chemical Physics publishes concise and definitive reports of significant research in the methods and applications of chemical physics. See: http://jcp.aip.org

Media Contact

Jason Socrates Bardi
jbardi@aip.org
240-535-4954

 @jasonbardi

http://www.aip.org 

Jason Socrates Bardi | EurekAlert!

Further reports about: Chemical Physics Humidity color change fibers microscopic orientation physics pitch wavelength

More articles from Physics and Astronomy:

nachricht Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst

nachricht Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>