June 18, 2009

Material can change color instantly

U.S. scientists say they have created a fabricated material that changes color instantly in response to an external magnetic field.

The researchers -- led by the University of California-Riverside Assistant Professor Yadong Yin -- said the fabricated microscopic polymer beads change color instantly and reversibly when external magnetic fields acting upon the microspheres change orientation.

The beads or magnetochromatic microspheres have excellent structural stability, the researchers said, and are highly compatible with various types of dispersion media such as water, alcohol, hexane and even polymer solutions.

Unlike many conventional approaches, the instantaneous color change occurs with no change in the structure or intrinsic properties of the microspheres themselves, said Yin. "What changes instead are the magnetic fields acting externally on the orientation of these microspheres, these photonic crystals.

Our work, added Yin, 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.

The study that included researchers from South Korea's Seoul National University is reported in the online edition of the Journal of the American Chemical Society.