University of California, Riverside nanotechnologists have succeeded in controlling the color of very small particles of iron oxide suspended in water simply by applying an external magnetic field to the solution. The discovery has potential to greatly improve the quality and size of electronic display screens and to enable the manufacture of products such as erasable and rewritable electronic paper and ink that can change color electromagnetically.
In their experiments, the researchers found that by changing the strength of the magnetic field they were able to change the color of the iron oxide solution -- similar to adjusting the color of a television screen image.
When the strength of the magnetic field is changed, it alters the arrangement of the spherical iron oxide particles in solution, thereby modifying how light falling on the particles passes through or is deflected by the solution.
Study results appear in Angewandte Chemie International Edition's online edition today. The research paper is scheduled to appear in print in issue 34 of the journal. Identified by Angewandte Chemie as a "very important paper," the research will be featured on the inside cover of the print issue.
"The key is to design the structure of iron oxide nanoparticles through chemical synthesis so that these nanoparticles self-assemble into three-dimensionally ordered colloidal crystals in a magnetic field," said Yadong Yin, an assistant professor of chemistry who led the research.
"By reflecting light, these crystals -- also called photonic crystals -- show brilliant colors," Yin said. "Ours is the first report of a photonic crystal that is fully tunable in the visible range of the electromagnetic spectrum, from violet light to red light."
A photonic crystal controls the flow of light (photons) and works like a semiconductor for light. The nanoparticles' spacing dictates the wavelength of light that a photonic crystal reflects.
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