The researchers reveal the secret of their success in the journal Angewandte Chemie: their “photonic pigments” are microcapsules filled with densely packed core–shell colloidal particles.
Conventional coloring agents have a variety of disadvantages: organic dyes tend to fade; inorganic pigments are often based on toxic heavy metals such as chromium. The color we see results from the absorption of a portion of the visible light spectrum. The reflected portions add to the color observed.
Another way to produce color that works without absorption is widely found in nature – in butterflies, for example. Arrays of nanoscopic particles can appear to be colored as a result of wavelength-dependent optical interference, refraction, and light scattering.
The color depends on the size of the particles. However, such structural pigments iridesce, meaning that the observed color varies in accordance with the angle of illumination or the viewing angle. In displays and many other applications, this would naturally be very annoying. The high degree of order in the particles of the crystal lattice contributes to this problem.
It is thus desirable to have the particles in a noncrystalline, amorphous arrangement, which is very difficult to achieve. In addition, amorphous structural pigments have thus far had very unsatisfactory color saturation caused by so called multiple scattering. A second type of undesired scattering, so-called incoherent scattering, contributes to a blueish background color that makes it difficult to produce a full spectrum of colors, particularly red.
A team from Harvard University (USA), the Korea Advanced Institute of Science and Technology, and the Korea Electronics Technology Institute has now solved these problems. Their success is due to microcapsules packed with nanoscopic polymer spheres whose core and shell are made of two different polymers. Led by Vinothan N. Manoharan, the scientists designed the shells to have the same refractive index as the surrounding aqueous medium.
The light is thus only scattered by the cores, whose size and distance from each other determine the scattering properties. In a dense packing arrangement, the distance between cores can be determined by the thickness of the shells. If the cores are very small and the shells relatively thick, the undesired types of scattering can be minimized while the desired coherent scattering that is responsible for the structural color dominates.
By using a microfluidic technique, tiny droplets of an aqueous suspension of the core–shell particles are coated with a thin film of oil. They are then shrunken through osmosis until the particles adopt a densely packed arrangement. The soft polymer shells of the particles prevent crystallization. In the last step, the oil film is cured with UV light to make delicate, transparent, capsules.The color of the novel structural pigments can be varied over the entire spectrum by changing the distances of the particle cores from each other by means of the thickness of the shells. The goal is to use these new nanoparticles in reflective displays.
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201309306
Novel 'repair system' discovered in algae may yield new tools for biotechnology
29.07.2016 | Boyce Thompson Institute
Molecular troublemakers instead of antibiotics?
29.07.2016 | Christian-Albrechts-Universität zu Kiel
Transparent electronics devices are present in today’s thin film displays, solar cells, and touchscreens. The future will bring flexible versions of such devices. Their production requires printable materials that are transparent and remain highly conductive even when deformed. Researchers at INM – Leibniz Institute for New Materials have combined a new self-assembling nano ink with an imprint process to create flexible conductive grids with a resolution below one micrometer.
To print the grids, an ink of gold nanowires is applied to a substrate. A structured stamp is pressed on the substrate and forces the ink into a pattern. “The...
A new Fraunhofer MEVIS method conveys medical interrelationships quickly and intuitively with innovative visualization technology
On the monitor, a brain spins slowly and can be examined from every angle. Suddenly, some sections start glowing, first on the side and then the entire back of...
Researchers at the U.S. Department of Energy's (DOE) Ames Laboratory have discovered an unusual property of purple bronze that may point to new ways to achieve high temperature superconductivity.
While studying purple bronze, a molybdenum oxide, researchers discovered an unconventional charge density wave on its surface.
Munich Physicists have developed a novel electron microscope that can visualize electromagnetic fields oscillating at frequencies of billions of cycles per second.
Temporally varying electromagnetic fields are the driving force behind the whole of electronics. Their polarities can change at mind-bogglingly fast rates, and...
Breakup of continents with two speed: Continents initially stretch very slowly along the future splitting zone, but then move apart very quickly before the onset of rupture. The final speed can be up to 20 times faster than in the first, slow extension phase.phases
Present-day continents were shaped hundreds of millions of years ago as the supercontinent Pangaea broke apart. Derived from Pangaea’s main fragments Gondwana...
29.07.2016 | Event News
15.07.2016 | Event News
15.07.2016 | Event News
29.07.2016 | Power and Electrical Engineering
29.07.2016 | Life Sciences
29.07.2016 | Event News