Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Polymer opal films shed new kind of light on nature

24.07.2007
New color-changing technology has potential packaging, military, aerospace applications

Imagine cleaning out your refrigerator and being able to tell at a glance whether perishable food items have spoiled, because the packaging has changed its color, or being able to tell if your dollar bill is counterfeit simply by stretching it to see if it changes hue.

These are just two of the promising commercial applications for a new type of flexible plastic film developed by scientists at the University of Southampton in the United Kingdom and the Deutsches Kunststoff-Institut (DKI) in Darmstadt, Germany. Combining the best of natural and manmade optical effects, their films essentially represent a new way for objects to precisely change their color. The researchers will publish their findings in the July 23 issue of Optics Express, an open-access journal of the Optical Society of America.

These "polymer opal films" belong to a class of materials known as photonic crystals. Such crystals are built of many tiny repeating units, and are usually associated with a large contrast in the components’ optical properties, leading to a range of frequencies, called a "photonic bandgap," where no light can propagate in any direction. Instead, these new opal films have a small contrast in their optical properties. As with other artificial opal structures, they are also "self-assembling," in that the small constituent particles assemble themselves in a regular structure. But this self-assembly is not perfect, and though meant to be periodic, they have significant irregularities. In these materials, the interplay between the periodic order, the irregularities, and the scattering of small inclusions strongly affect the way the light travels through these films, just as in natural opal gem stones, a distant cousin of these materials. For example, light may be reflected in unexpected directions that depend on the light's wavelength.

Photonic crystals have been of interest for years for various practical applications, most notably in fiber optic telecommunications but also as a potential replacement for toxic and expensive dyes used for coloring objects, from clothes to buildings. Yet much of their commercial potential has yet to be realized because the colors in manmade films made from photonic crystals depend strongly on viewing angle. If you hold up a sheet of the opal film, Baumberg explains, “You’ll only see milky white, unless you look at a light reflected in it, in which case certain colors from the light source will be preferentially reflected.” In other words, change the angle, and the color changes.

These photonic crystals are apparent in the natural world as well but are more consistent in color at varying angles. Opals, butterfly wings, certain species of beetle, and peacock feathers all feature arrays of tiny holes, neatly arranged into patterns. Even though these natural structures aren’t nearly as precisely ordered as the manmade versions, the colors produced are unusually strong, and depend less on the viewing angle.

Until now, scientists believed that the same effect was at work in both manmade and natural photonic crystals: the lattice structure caused the light to reflect off the surface in such a way as to produce a color that changes depending upon the angle of reflection. Baumberg, however, suspects that the natural structures selectively scatter rather than reflect the light, a result of complex interplay between the order and the irregulaty in these structures.

Given that hunch, Baumberg’s team developed polymer opals to combine the precise structure of manmade photonic crystals with the robust color of natural structures. The polymer opal films are made of arrays of spheres stacked in three dimensions, rather than layers. They also contain tiny carbon nanoparticles wedged between the spheres, so light doesn’t just reflect at the interfaces between the plastic spheres and the surrounding materials, it also scatters off the nanoparticles embedded between the spheres. This makes the film intensely colored, even though they are made from only transparent and black components, which are environmentally benign. Additionally, the material can be "tuned" to only scatter certain frequencies of light simply by making the spheres larger or smaller.

In collaboration with scientists at DKI in Darmstadt, Germany, Baumberg and his colleagues have developed a solution for another factor that traditionally has limited the commercial potential of photonic crystals: the ability to mass-produce them. His Darmstadt colleagues have developed a manufacturing process that can be successfully applied to photonic crystals and they now can produce very long rolls of polymer opal films.

The films are "quite stretchy," according to Baumberg, and when they stretch, they change color, since the act of stretching changes the distance between the spheres that make up the lattice structure. This, too, makes them ideal for a wide range of applications, including potential ones in food packaging, counterfeit identification and even defense.

Colleen Morrison | EurekAlert!
Further information:
http://www.osa.org
http://www.nano.soton.ac.uk/opal.html
http://www.opticsexpress.org/abstract.cfm?id=139950

More articles from Materials Sciences:

nachricht Physics, photosynthesis and solar cells
01.12.2016 | University of California - Riverside

nachricht New process produces hydrogen at much lower temperature
01.12.2016 | Waseda University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>