New fabricated material changes color instantly in response to external magnetic field

The beads or "magnetochromatic microspheres" have excellent structural stability. They also are highly compatible with various types of dispersion media such as water, alcohol, hexane and even polymer solutions, allowing them to retain magnetically tunable colors in a variety of chemical environments.

"Unlike many conventional approaches, the instantaneous color change occurs with no change in the structure or intrinsic properties of the microspheres themselves," said Yadong Yin, an assistant professor of chemistry who led the study that brought together chemists at UCR and engineers at Seoul National University, South Korea. "What changes instead are the magnetic fields acting externally on the orientation of these microspheres, these photonic crystals. Our work provides a new mechanism for inducing color change in materials. Now, for the first time, stable photonic materials with tunable colors can be fabricated on a large scale."

Applications of the new material include display type units such as rewritable or reusable signage, posters, papers and labels, and other magnetically activated security features. The new material also can be used to make environmentally friendly pigments for paints and cosmetics, as well as ink materials for color printing.

"Within a certain range, it is possible also to tune the color of the material by simply rotating the microspheres," Yin said.

Study results appeared June 15 in the online issue of the Journal of the American Chemical Society.

"The new technology has a great potential for a wide range of photonic applications because the on/off switching of the diffraction color by the rotating photonic sphere is fast, greatly simplifying the pixel structures," said Seoul National University's Sunghoon Kwon, a leading expert in biophotonics and nanoengineering, whose lab collaborated with Yin's lab on the research. "Therefore, the new technology is suitable for very large-scale displays, such as active signage."