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 Writing and deleting magnets with lasers
19.04.2018 | Helmholtz-Zentrum Dresden-Rossendorf

nachricht Ultrafast electron oscillation and dephasing monitored by attosecond light source
19.04.2018 | Yokohama National University

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: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Scientists re-create brain neurons to study obesity and personalize treatment

20.04.2018 | Health and Medicine

Spider silk key to new bone-fixing composite

20.04.2018 | Materials Sciences

Clear as mud: Desiccation cracks help reveal the shape of water on Mars

20.04.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>