doi:10.1038/nindia.2017.136 Published online 25 October 2017
Physicists have synthesized a nanoparticles-based liquid mirror that can be electrically tuned to transmit or reflect light, making it potentially useful for fabricating a switchable window-mirror device1.
The nanoparticles in this case are metamaterials — artificially structured materials used to control and manipulate light and sound. They can make things invisible and may even catch minute details of objects that no other sophisticated optical microscope can.
Although advances have been made, tuning and modulating the optical properties of metamaterials in real time remain a challenge.
Scientists from the Indian Institute of Technology Guhawati in India and Imperial College London in United Kingdom have developed a system containing modified gold nanoparticles and two immiscible layers of electrolytes. They then electrically tuned the assembly and disassembly of the nanoparticles by altering the applied potential.
At negative potential values, the nanoparticles assembled towards the electrolyte layers, forming a dense layer; at positive potential values, the nanoparticles disassembled. Like a mirror, the dense layer reflected light, while disassembled nanoparticles transmitted light the way a window does.
Exploiting these optical properties, the researchers made a prototype electrically switchable liquid window-mirror device. A coin was placed to face the liquid mirror and a currency note was placed at the back of the mirror.
At positive potential values, the nanoparticles disassembled and transmitted light, showing the presence of the currency note. At negative potential values, the nanoparticles assembled and formed a dense layer that reflected light, making the coin visible.
1. Montelongo, Y. et al. Electrotunable nanoplasmonic liquid mirror. Nat. Mater. (2017) doi: 10.1038/nmat4969