Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Color without Dyes: New non-iridescent structural colors cover the whole spectrum

Free of dyes but colorful: A team of American and Korean researchers is the first to develop non-iridescent, structural, full-spectrum pigments, whose color is independent of the viewing angle, for use in reflective displays.

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.

About the Author
Vinothan N. Manoharan is the Gordon McKay Professor of Chemical Engineering and Professor of Physics at Harvard University. His research focuses on understanding the physics of self-assembly and controlling self-assembly processes to make interesting materials.
Author: Vinothan N. Manoharan, Harvard University, Cambridge (USA),
Title: Full-Spectrum Photonic Pigments with Non-iridescent Structural Colors through Colloidal Assembly

Angewandte Chemie International Edition, Permalink to the article:

Vinothan N. Manoharan | Angewandte Chemie
Further information:

More articles from Life Sciences:

nachricht New study reveals what's behind a tarantula's blue hue
01.12.2015 | University of California - San Diego

nachricht Tracing a path toward neuronal cell death
01.12.2015 | Brigham and Women's Hospital

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: How do Landslides control the weathering of rocks?

Chemical weathering in mountains depends on the process of erosion.

Chemical weathering of rocks over geological time scales is an important control on the stability of the climate. This weathering is, in turn, highly dependent...

Im Focus: How Cells in the Developing Ear ‘Practice’ Hearing

Before the fluid of the middle ear drains and sound waves penetrate for the first time, the inner ear cells of newborn rodents practice for their big debut. Researchers at Johns Hopkins report they have figured out the molecular chain of events that enables the cells to make “sounds” on their own, essentially “practicing” their ability to process sounds in the world around them.

The researchers, who describe their experiments in the Dec. 3 edition of the journal Cell, show how hair cells in the inner ear can be activated in the absence...

Im Focus: Climate study finds evidence of global shift in the 1980s

Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.

Scientists say that a major step change, or ‘regime shift’, in the Earth’s biophysical systems, from the upper atmosphere to the depths of the ocean and from...

Im Focus: Innovative Photovoltaics – from the Lab to the Façade

Fraunhofer ISE Demonstrates New Cell and Module Technologies on its Outer Building Façade

The Fraunhofer Institute for Solar Energy Systems ISE has installed 70 photovoltaic modules on the outer façade of one of its lab buildings. The modules were...

Im Focus: Lactate for Brain Energy

Nerve cells cover their high energy demand with glucose and lactate. Scientists of the University of Zurich now provide new support for this. They show for the first time in the intact mouse brain evidence for an exchange of lactate between different brain cells. With this study they were able to confirm a 20-year old hypothesis.

In comparison to other organs, the human brain has the highest energy requirements. The supply of energy for nerve cells and the particular role of lactic acid...

All Focus news of the innovation-report >>>



Event News

European Geosciences Union meeting: Media registration now open (EGU 2016 media advisory 1)

01.12.2015 | Event News

Urbanisation and migration from rural areas challenging agriculture in Eastern Europe

30.11.2015 | Event News

Fraunhofer’s Urban Futures Conference: 2 days in the city of the future

25.11.2015 | Event News

Latest News

USGS projects large loss of Alaska permafrost by 2100

01.12.2015 | Earth Sciences

New study reveals what's behind a tarantula's blue hue

01.12.2015 | Life Sciences

Climate Can Grind Mountains Faster Than They Can Be Rebuilt

01.12.2015 | Earth Sciences

More VideoLinks >>>