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Optoelectronics/Displays??

Chemists unveil magnetically-responsive liquid crystals

Posted: 01 Jul 2014 ?? ?Print Version ?Bookmark and Share

Keywords:University of California? liquid crystal? magnetic field? nanorod?

First, they can be operated remotely by an external magnetic field, with no electrodes needed. (Electrical switching of commercial liquid crystals requires transparent electrodes which are very expensive to make.) Second, the nanorods are much larger than the molecules used in commercial liquid crystals. As a result, their orientation can be conveniently fixed by solidifying the dispersing matrix.

Further, the magnetic nanorods can be used to produce thin-film liquid crystals, the orientation of which can be fixed entirely or in just selected areas by combining magnetic alignment and lithographic processes. This allows patterns of different polarizations to be created as well as control over the transmittance of polarised light in select areas.

Yadong Yin

Yadong Yin is an associate professor of chemistry at UC Riverside. Photo credit: L. Duka.

"Such a thin film does not display visual information under normal light, but shows high contrast patterns under polarised light, making it immediately very useful for anti-counterfeit applications," Yin said. "This is not possible with commercial liquid crystals. In addition, the materials involved in our magnetic liquid crystals are made of iron oxide and silica, which are much cheaper and more eco-friendly than the commercial organic molecules-based liquid crystals."

The liquid crystals may also find applications as optical modulators, optical communication devices for controlling the amplitude, phase, polarisation, propagation direction of light.

The discovery came about when Yin's lab first had the idea of using magnetic nanorods to replace rod-shaped molecules in commercial systems to produce liquid crystals that can be magnetically controlled. After looking into the literature, the research team realised that the main challenge in producing practically useful magnetic liquid crystals was in the synthesis of magnetic nanorods.

"Prior attempts had been limited to materials with very limited magnetic responses," Yin said. "We utilised our expertise in colloidal nanostructure synthesis to produce magnetite nanorods that can form liquid crystals and respond strongly to even very weak magnetic fields, even a fridge magnet can operate our liquid crystals."

The research was supported by grants to Yin by the National Science Foundation and the U.S. Army Research Laboratory.

Yin was joined in the research by Mingsheng Wang and Le He at UCR; and Serkan Zorba at Whittier College, Calif.

The UCR Office of Technology Commercialisation has filed a patent on the technology reported in the research paper.


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