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 First time-lapse footage of cell activity during limb regeneration
25.10.2016 | eLife

nachricht Phenotype at the push of a button
25.10.2016 | Institut für Pflanzenbiochemie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

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

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Ice shelf vibrations cause unusual waves in Antarctic atmosphere

25.10.2016 | Earth Sciences

Fluorescent holography: Upending the world of biological imaging

25.10.2016 | Power and Electrical Engineering

Etching Microstructures with Lasers

25.10.2016 | Process Engineering

More VideoLinks >>>