Nature News reports that British and Canadian chemists have developed synthetic opals that can very quickly switch between various colors when a few volts of electricity are applied to them. The developers, who said they're ready to sell the technology today, added that their 'photonic ink' (P-Ink) material could soon be used in electronic books or advertising displays. These modified opals could also be used to build the next generation of flexible solar cells. ...
The figure above shows "the process of chemically transforming an opal (left) into a composite opal (middle) where the spheres and infiltrated material are colored white and green, respectively, and finally an inverse opal (right) where the spheres have been etched away, leaving behind the replica material." (Credit: Geoffrey Ozin and Andre Arsenault) Here is a link to a larger version of this illustration.
This second figure describes how the P-Ink technology works. This "is an opal-based technology that provides electrically tunable color of any wavelength. By coating this material onto an array of pixels, a full-color display can be created wherein the color of each pixel can be varied at will. Switching of a P-Ink pixel in response to a voltage increasing from left to right." (Credit: Geoffrey Ozin and Andre Arsenault) Here is a link to a larger version of this illustration.
This research project is beeing led by Geoffrey Ozin, a chemist at the University of Toronto, Canada, and his group, and by Ian Manners of the University of Bristol, UK, and his own group. The project also involved André Arsenault of Opalux, a Toronto-based start-up company which was spun off from the University of Toronto, and by Daniel Puzzo, of the Department of Chemistry at the University of Toronto.
So will we soon see applications of the P-Ink technology? "Electronic inks are already used in commercial products such as Amazon's Kindle reader. Most current technologies use an electric field to manipulate drops of oil or pigment particles. The presence or absence of a voltage makes pixels on the display appear light or dark, and most displays are confined to monochrome. P-Ink, however, can display any colour without using pigments. Instead, it relies on the same effect that generates shimmering colours in the semi-precious stone, opal."
And how did the chemists develop this new material? "The scientists make the materials by first stacking silica spheres 180 nanometres wide onto a glass plate to form a template. They then add an electroactive polymer containing iron atoms, which forms a gel around the spheres. When the material is incorporated into an electrical cell with a liquid electrolyte, applying a voltage causes electrons to move between the iron atoms and the electrolyte. This moves liquid around within the polymer gel, causing it to swell or contract, and altering its optical properties so that different wavelengths of light are reflected."
In Chameleon-like 'opal' can take on any colour, New Scientist provides other details -- and a short video.
Here is a description of the fabricating process. "The starting point for the new material is a stack of silica marbles, each 270 nanometres across, on a flat electrode. A polymer is added on top to encase the spheres and to hold them in place. Next, the spheres are dissolved with acid to leave behind a regular pattern of air pockets inside the polymer. Finally, these pockets are filled with a liquid electrolyte and the structure is sealed. The result behaves just like an opal. The polymer and electrolyte have different refractive indexes, and their repeating pattern scatters only blue photons to make the material an iridescent blue. But when a voltage is applied, the material becomes red, flitting across every other colour in the visible spectrum along the way."
And here is a quote from Arsenault about this new material. "'Given the current switching speeds, an ideal first product may be something like full-colour electronic paper,' he says. Although a pulse of voltage is needed to shift the colour, maintaining it in a given state requires no energy at all. And because the material's colour comes from the way it scatters light that falls on it, rather than emitting light like a conventional display, it could be perfectly readable in bright light."
This latest research work has been published online on December 3, 2008 by Angewandte Chemie International Edition under the title "Electroactive Inverse Opal: A Single Material for All Colors." Here is a link to this paper only freely available to Inderscience customers.
You also might want to read another article from Materials Today, "P-Ink and Elast-Ink from lab to market" (Volume 11, Issues 7-8, July-August 2008, Pages 44-51). Here is a link to the full paper, from which the two above figures have been extracted.
Sources: Geoff Brumfiel, Nature News, December 23, 2008; Colin Barras, New Scientist, December 23, 2008; and various websites
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