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Researchers create a dynamically switchable mirror

Dynamically switchable mirrors

Researchers have developed a method to dynamically change the surface of liquid metal between reflection and scattering states. One day, this technology could be used to make electronically controlled mirrors or lighting equipment. Liquid metal combines the electrical, thermal, and optical properties of the metal with the fluidity of the liquid.

The new method uses electrochemical reactions to create interchangeable reflective surfaces on liquid metal. No optical coating or polishing steps are required. Reflective optical components need to be manufactured to make liquid metal high-reflectivity mirrors that can switch between reflection and scattering Optical Materials Express (OSA) Optical Materials Express magazine shows that researchers led by Yuji Oki of the School of Computer Science and Electrical Engineering at Kyushu University only need 1.4V can switch between reflection and scattering states, which is roughly the same voltage used to power typical LEDs.

The researchers worked with the Michael D. Dickey research team of North Carolina State University to develop a new method that can be implemented at ambient temperature and pressure. In this new work, the researchers created a reservoir with embedded flow channels and then used the “push-off method” to shape the optical surface by pumping or sucking liquid gallium-based metal into the reservoir.

Convex, flat, or concave; each has different optical properties. The researchers then used electricity to trigger a chemical reaction to reversibly oxidize the liquid metal. Oxidation changes the volume of the liquid, causing many small scratches that scatter light on the surface. The liquid metal deposited in the opposite direction returns to its original state. The surface tension of the liquid metal makes the scratches disappear and the surface becomes a clean mirror.

Researchers have characterized various surfaces produced by electrochemistry and optics. They found that when the surface changes from reflective to diffuse, changing the surface tension from -800 mV to +800 mV reduces the light intensity. The electrochemical measurement shows a voltage change of 1.4 V is sufficient to produce redox reactions with good reproducibility.

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