14 DAY TRIAL // A liquid that changes its color when exposed to a magnetic field, recently discovered by U.S. researchers, could easily and cheaply replace the color components of computer LCD displays. The liquid is in fact a suspension of tiny iron particles coated in a special plastic, and because it is so cheap and easy to make, its applications could be very numerous.
Yadong Yin and colleagues at the Department of Chemistry at University of California, Riverside, US, created the liquid by coating particles of iron oxide - each about 100 nanometres in diameter - with a polymer and suspending the mixture in water. Because of the plastic coating, each iron particle has a highly charged surface and since all of them are of the same charge, they will repel each other, until exposed to a magnetic field. The opposing forces, electrostatic repulsion and magnetic attraction will force the tiny particles to arrange themselves into a "photonic crystal", that reflects light because the space between particles is the same as the wavelength of visual light. Varying the strength of the magnetic field applied to the crystal will result in alterations of the distance between particles and so the wavelength, or color, of the light that is reflected.
As the magnetic field increases, the crystals in the liquid suspension are reflecting brilliant colors ranging from red to violet and when the magnetic influence ceases, the liquid returns to its natural, brownish color. "This is the first report of a photonic crystal that is fully tuneable in the visible range of the electromagnetic spectrum," says Yin.
"We see applications in various areas, including sensors, optical switches and flexible colour displays," he told New Scientist. "For example, the system can be used to make extra-large displays or posters to replace expensive LCD monitors. And, because the colour is based on reflection, it is better for outdoor applications than current LCD displays that perform poorly in direct sunlight."
A color-display would contain millions of small pixels made from the photonic crystals, explains Yin, with each pixel being assigned a different color using a distinct magnetic field.