Photonic ink (P-Ink) is a substance that can change color electronically. Unlike earlier prototype electronic ink s, which could only display two color values (usually black and white), photonic ink can display any color value in the spectrum. Among other applications, photonic ink could be used for refreshable, full-color images in an electronic newspaper, to coordinate pictures with updated newspaper content. Ian Manners, Geoffrey Ozin, and colleagues are developing photonic ink at the University of Toronto in Canada.
Photonics (from photon ) is an area of study centering around the generation and utilization of radiant energy , such as light , for various applications. Photonic ink displays color through controlled diffraction, a special type of interference that is responsible for the iridescent color effects of opals and butterfly wings. Here's how it works: particles are stacked in a uniform pattern, similarly to the way any round objects, such as oranges or basketballs, are organized when stacked. Interference occurs when light is deflected by the particles; this deflection causes some wavelengths to be eliminated, which results in the reflected light appearing as a particular color. Varying the size of the spaces between the particles creates different colors.
To make the colors tunable, the researchers packed a polymer gel between the stacked spheres. The gel, which swells when soaked in a solvent and then shrinks again when it dries out, creates variances in the spacing between the tiny spheres. Because the size of the spaces determines the wavelength that will be reflected, the swelling and drying of the gel (which occurs in less than a second) results in a tunable display of color. The amount of solvent that the gel absorbs is controlled by applying an electrical voltage; variation of the voltage makes it possible to tune the ink to any shade in the color spectrum.