Magnets can change the color of liquids

The University of California, Riverside nanologists have succeeded in controlling the color of tiny iron oxide particles suspended in water simply by applying an external magnetic field to the solution. This discovery has the potential to significantly improve the quality and size of electronic screens and is capable of creating erasable and rewritten electronic and paper products, color-changing products in the same way. electromagnetic.

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

As the color of the magnetic field changes, it changes the arrangement of spherical iron oxide particles in solution, and thus changes the way light shines through these particles or changes the way light is deflected by the solution. direction.

'The method is to create the structure of iron oxide nanoparticles through chemical synthesis so that these nanoparticles assemble themselves into three-dimensional colloidal crystals in the magnetic field,' said Yadong Yin, the dean. The chemistry professor of the research team spoke.

The image shows that the solution of iron oxide changes color under the effect of magnetic fields, with the magnetic field intensity increasing from left to right.(Photos: Yin laboratory, UCR)

Nanoparticles are tiny particles with dimensions measured in nanometers. Colloids are a substance consisting 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 - create beautiful colors,' Yin said. 'Our research is the first study to detect photonic crystals that can be perfectly navigable in a visible range of electromagnetic spectra, from violet light to red light.'

A photonic crystal controls the light flow (photon) and acts like a light semiconductor. The distance of nanoparticles controls the wavelength of light that photonic crystals reflect.

The nanoparticles of Iron oxide (formula: Fe ₃ O ₄ ) are ' superparamagnetic ' meaning they only switch from being magnetic to the presence of an external magnetic field. In contrast, ' ferromagnetic material' becomes magnetized in magnetic fields and maintains their magnetism when the magnetic field is lost.

Scientists use the superparamagnetic property of iron oxide particles to adjust the distance between nanoparticles, and thereby adjust the wavelength of light reflection - or the color of colloidal crystals - by how to change the intensity of the external magnetic field.

'Previously studied photonic crystals can only reflect light with a fixed wavelength,' Yin said. 'Our crystals, on the other hand, have fast, wide optical reactions and can return to the same way when exposed to magnetic fields from the outside.'

Photonic materials such as those used by Associate Professor Yin and his team help create new microelectromechanical systems and color display units. They also have applications in telecommunications (fiber optics), sensors and lasers.

' This is a simple method that allows researchers to pair photonic crystals and control the distance between them by using magnetic fields ,' said Associate Professor of Molecular and Chemical Biological Engineering at the University. University of North Carolina State, Raleigh, NC, said. 'A simple magnet is used to change the color of a suspension throughout the entire visible spectrum. This is capable of creating precursors to various photonic devices. '

'And what makes this technology commercially attractive is that iron oxide is cheap, non-toxic and readily available,' Yin said.

Yin explained that the new technique will be used to create an inexpensive color screen by forming millions of tiny pixels using photonic crystals.'It is possible to create a different color per pixel using magnetic fields,' he said. 'The advantage is that you only need one material - for example, photonic crystals are like iron oxide - for all pixels. Also, you do not need to transmit light at every pixel. You will use reflected light to create images - a form of recycling. '

The University of California, Riverside's Office of Technology Chemistry and Technology applied for a patent for this technology.

Thanh Van