Iron oxide particles embedded in microscopic polymer beads can be made to change color with the application of external magnetic fields, according to the team led by Yadong Yin at the University of California.
“Unlike many conventional approaches, the instantaneous color change occurs with no change in the structure or intrinsic properties of the microspheres themselves. What changes instead are the magnetic fields acting externally on the orientation of these microspheres,” explained Yin.
The magnetic field makes the particles line up in ordered arrangements. Changing the field will change the order of the particles leading to different diffraction colours, according to the study.
“The good thing about this technique is that we can make the iron oxide itself into different colors just using magnetic fields, avoiding the use of additional materials that in dye production are sometimes toxic” Yin told CosmeticsDesign.
Theoretically any color can be produced, Yin said; however, in order to get the full spectrum different particle sizes of the iron oxide would be needed.
The simplest application for the technology would be to apply the magnetic field during production in order to create environmentally friendly pigments.
However, with a little bit more engineering it is possible to create pigments that can be turned on and off after production with the application of magnetic fields, said Yin.
“We can imagine a nail varnish whose colour could be turned on or off when exposed to different magnetic forces,” he said.
Other applications for the technology include rewritable display units, signage, posters and labels, where the color can be turned on and off with the application of a magnetic field.
The original discovery that ordering particles with magnetic fields can change the color was made a few years ago, explained Yin.
However, this is the first time they have been embedded into polymer microspheres and shown to be producible on a large scale, said Yin, who is hoping for significant industry interest in the research.
Source: Journal of the American Chemical Society
Magnetochromatic Microsheres: Rotating Photonic Crystals
Jianping Ge, Howon Lee, Le He, Junhoi Kim, Zhenda Lu, Hyoki Kim, James Goebl, Sunghoon Kwon, and Yadong Yin