Simple Magnet Can Control Color of Liquid

July 3, 2007
Simple Magnet Can Control the Color of a Liquid
Image shows the solution of iron oxide in water changing color under a magnetic field, with increasing strength of the field from left to right. Photo credit: Yin laboratory, UCR

University of California, Riverside nanotechnologists have succeeded in controlling the color of very small particles of iron oxide suspended in water simply by applying an external magnetic field to the solution. The discovery has potential to greatly improve the quality and size of electronic display screens and to enable the manufacture of products such as erasable and rewritable electronic paper and ink that can change color eletromagnetically.

In their experiments, the researchers found that by changing the strength of the magnetic field they were able to change the color of the iron oxide solution – similar to adjusting the color of a television screen image.

When the strength of the magnetic field is changed, it alters the arrangement of the spherical iron oxide particles in solution, thereby modifying how light falling on the particles passes through or is deflected by the solution.

Study results appear in Angewandte Chemie International Edition’s online edition today. The research paper is scheduled to appear in print in issue 34 of the journal. Identified by Angewandte Chemie as a “very important paper,” the research will be featured on the inside cover of the print issue.

“The key is to design the structure of iron oxide nanoparticles through chemical synthesis so that these nanoparticles self-assemble into three-dimensionally ordered colloidal crystals in a magnetic field,” said Yadong Yin, an assistant professor of chemistry who led the research.

A nanoparticle is a microscopic particle whose size is measured in nanometers.

A colloid is a substance comprised of small particles uniformly distributed in another substance. Milk, paint and blood are examples of colloids.

“By reflecting light, these crystals – also called photonic crystals – show brilliant colors,” Yin said. “Ours is the first report of a photonic crystal that is fully tunable in the visible range of the electromagnetic spectrum, from violet light to red light.”

A photonic crystal controls the flow of light (photons) and works like a semiconductor for light. The nanoparticles’ spacing dictates the wavelength of light that a photonic crystal reflects.

Iron oxide (formula: Fe3O4) nanoparticles are “superparamagnetic,” meaning that they turn magnetic only in the presence of an external magnetic field. In contrast, “ferromagnetic” materials become magnetized in a magnetic field and retain their magnetism when the field is removed.

The researchers used the superparamagnetic property of iron oxide particles to tune the spacing between nanoparticles, and therefore the wavelength of the light reflection – or the color of the colloidal crystals – by changing the strength of the external magnetic field.

“Other reported photonic crystals can only reflect light with a fixed wavelength,” Yin said. “Our crystals, on the other hand, show a rapid, wide and fully reversible optical response to the external magnetic field.”

Photonic materials such as those used by Yin and his team could help in the fabrication of new optical microelectromechanical systems and reflective color display units. They also have applications in telecommunication (fiber optics), sensors and lasers.

“This is an elegant method that allows researchers in the field to assemble photonic crystals and control their spacing by using a magnetic field,” said Orlin Velev, an associate professor of chemical and biomolecular engineering at North Carolina State University, Raleigh, N.C., who was not involved in the research. “A simple magnet can be used to change the color of a suspension throughout the whole visible spectra. This has potential to result in usable precursors for various photonic devices.”

“What should make the technology commercially attractive is that iron oxide is cheap, non-toxic and available in plenty,” Yin said.

Yin explained that the new technology can be used to make an inexpensive color display by forming millions of small pixels using the photonic crystals. “A different color for each pixel can be assigned using a magnetic field,” he said. “The advantage is that you need just one material – for example, photonic crystals like iron oxide – for all the pixels. Moreover, you don’t need to generate light in each pixel. You would be using reflected light to create the images – a form of recycling.”

The UCR Office of Technology Commercialization has filed a patent application on the technology.

Source: University of California, Riverside

Explore further: Review: New light bulbs offer alternative to LEDs and CFLs

Related Stories

Review: New light bulbs offer alternative to LEDs and CFLs

September 4, 2015

For consumers who are still bemoaning the phaseout of incandescent light bulbs, hate the harsh CFLs and can't figure out LEDs, another option may be on the horizon - a new kind of bulb is slated to hit store shelves this ...

X-ray laser pulses in two colors

March 27, 2013

( —SLAC researchers have demonstrated for the first time how to produce pairs of X-ray laser pulses in slightly different wavelengths, or colors, with finely adjustable intervals between them – a feat that will ...

Nanoscale zipper cavity responds to single photons of light

June 4, 2009

Physicists at the California Institute of Technology have developed a nanoscale device that can be used for force detection, optical communication, and more. The device exploits the mechanical properties of light to create ...

Into the magnetic blue yonder

December 1, 2011

Probing the quantum mechanics of magnetism is not for the faint of heart. Literally. The door to Madalina Furis’ laboratory on the fifth floor of the Cook Building has a sign that reads “Stop! No pacemakers beyond ...

Recommended for you

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...

New sensor sends electronic signal when estrogen is detected

November 24, 2015

Estrogen is a tiny molecule, but it can have big effects on humans and other animals. Estrogen is one of the main hormones that regulates the female reproductive system - it can be monitored to track human fertility and is ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.