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Smart liquid goes dark in the heat

A smart liquid that darkens dramatically in response to rising temperature has been developed by researchers at A*STAR. The nanowire-based thermochromic liquid's tunable color-changing behavior was retained even after hundreds of heat-cool cycles.

[...] Previous thermochromic liquids have usually been based on organic dyes or liquid crystals. Although amenable to industrial-scale production, organic dyes tend to degrade upon exposure to light, while liquid crystals require encapsulation to avoid degradation in air. A thermochromic liquid that overcomes these limitations has been discovered by Wen-Ya Wu and her colleagues from the A*STAR Institute of Materials Research and Engineering, in collaboration with researchers at the National University of Singapore.

Wu's research is focused on semiconductor nanocrystals, which form a colloidal suspension in certain solvents, and which are known for their broad light absorption and high photostability. "While exploring the synthesis of colloidal antimony selenide (Sb2Se3) nanoparticles, we serendipitously discovered that they formed crystalline nanowires upon heating and dissolved into their molecular precursors upon cooling, in a certain mixture of solvents," Wu says.

Thanks to their broad light-absorbing behavior, a vial of Sb2Se3 nanowires formed by heating can appear very dark. But a solution of their molecular precursors, which the nanowires revert to upon cooling, are relatively transparent. "This phenomenon formed the basis for developing these materials as liquid-based thermochromics," Wu says.

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