Materials

Liquid metal mirrors switch reflectivity on and off with a zap

Liquid metal mirrors switch re...
Samples of the liquid metal in its reflective state (top left/bottom right) and scattering state (top right/bottom left)
Samples of the liquid metal in its reflective state (top left/bottom right) and scattering state (top right/bottom left)
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Samples of the liquid metal in its reflective state (top left/bottom right) and scattering state (top right/bottom left)
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Samples of the liquid metal in its reflective state (top left/bottom right) and scattering state (top right/bottom left)

Engineers have found a way to make liquid metals switch between reflective surfaces or those that scatter light. The transition only requires a small zap of electricity and could be used to make mirrors that can be switched on or off.

Liquid metals conduct electricity and interact with heat and light in the same ways as their solid forms, but the added fluidity opens up a range of new devices that weren’t previously possible. In recent years the slippery shiny stuff has been used to make morphing electronics, stretchable wires, and better batteries.

And now, liquid metals might be able to add switchable reflectivity to their repertoire. Researchers from Kyushu University and North Carolina State University found that changing the voltage of electricity applied to liquid metal can make its surface change from reflective to scattering.

The electricity is oxidizing the metal, which causes its volume to change. That in turn produces a series of tiny “scratches” to appear on the surface, scattering the light randomly. To undo the changes and return the liquid metal to a reflective state, the magnitude of the voltage can be switched from negative to positive.

The switching can be done with a low voltage of just 1.4 V, on par with that used to power an LED. It can be done at room temperature and pressure too, all of which helps make it potentially useful for commercial applications, such as new electronic and optical components.

“In the immediate future this technology could be used to create tools for entertainment and artistic expression that have never been available before,” says Yuji Oki, lead researcher on the study. “With more development, it might be possible to expand this technology into something that works much like 3D printing for producing electronically controlled optics made of liquid metals. This could allow the optics used in light-based health testing devices to be easily and inexpensively fabricated in areas of the world that lack medical laboratory facilities.”

The research was published in the journal Optical Materials Express. The switching can be seen in action in the video below.

Dynamic Control of Reflective/Diffusive Optical Surfaces on Liquid Metal

Source: The Optical Society

1 comment
1 comment
Jinpa
Other than mercury, which metals are liquid at room temperature? Mercury and bromine, but bromine is a halogen, so not really a metal. Mercury is highly toxic. What ordinary uses could there be for mercury mirrors? Same for bromine, which is highly reactive? https://en.wikipedia.org/wiki/Bromine