Controlling Color with Magnets
New material can become any visible color

SOURCE: “Highly Tunable Superparamagnetic Colloidal Photonic Crystals”
Yadong Yin et al.
Angewandte Chemie International Edition online, July 3, 2007

RESULTS: Researchers at the University of California, Riverside, have demonstrated that a liquid containing suspended mag­netite particles changes colors in the presence of an electromagnet. The liquid can be made to reflect any ­visible color and can switch colors at a rate of twice per second.

WHY IT MATTERS: Others have made magnetically controlled color-changing materials, but the colors covered only small parts of the spectrum, and the materials took longer to switch colors than the Riverside researchers’ do. The new materials could be used as sensors that register changes in magnetic fields. And microcapsules full of the liquids could eventually be used as pixels in rewritable posters or other large displays.

METHODS: The researchers used a new high-temperature method to synthesize nanoscale, crystalline magnetite particles, which were then induced to form clusters. The researchers treated the clusters with a surfactant that creates an electric charge on their surfaces. This charge repels neighboring clusters. They then applied a magnetic field, counteracting the repellent forces; the stronger the field is, the closer together the clusters get. As the clusters rearrange themselves, the solution they’re suspended in reflects light of different colors.

NEXT STEPS: The researchers hope to increase switching speeds by confining smaller amounts of material in microscopic spaces. They are also developing applications such as sensors and displays.