Researchers from the Department of Chemistry at the University of California, Riverside, have developed a type of liquid that has the ability to change color when treated with a magnetic force. The liquid is composed of iron oxide particles, each about 100nm in diameter, coated with plastic and suspended in water. Leading researcher Yadong Yin and colleagues argue that the liquid could replace the color components of conventional LCD monitors as a more economic alternative.
"'It is cheap and easy to make, and could also be used in flexible, rewritable, electronic paper, the researchers says.'"
"'We see applications in various areas, including sensors, optical switches and flexible colour displays… 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.'"
In the solution the particles repel each other because they carry the same charge, but iron oxide is magnetic so the particles will coalesce when treated with a magnetic force. As the electrostatic and magnetic forces oppose each other, the result is the particles arranging themselves into a highly ordered structured called a “colloidal photonic crystal.” The significance of the crystal structure is that it reflects light since the distance between crystals is equal to the wavelength of light. The distance between crystals can be manipulated easily - by changing the strength of the magnetic field - such that various colors can be reflected.
"'A colour display would contain millions of small pixels made from the photonic crystals,' explains Yin, with each pixel being assigned a different colour using a distinct magnetic field."