New Nanomaterial changes from hard to soft

Conversely, fractureresistant materials that absorb energy when they are deformed lack strength. Materials researchers have now developed a material that can switch back and forth between the mechanical properties of strong and ductile. Dr. Jörg Weißmüller, affiliated with both the Helmholtz-Zentrum Geesthacht (HZG) and the Hamburg University of Technology, worked together with Dr. Haijun Jin from the Institute of Metal Research in Shenyang, China, to achieve this breakthrough, which utilises the process of corrosion. They placed noble metals such as gold and platinum in an acidic solution, precisely controlling the resulting corrosion so that a network of porous channels only a few atoms wide was etched into the metal. They then filled the channels with a conductive liquid such as a saline solution or a diluted acid. The result is a hybrid material consisting of metal and liquid in which ions dissolved in the liquid can move freely and transport electric signals. The application of an external voltage produces an electric spacecharge layer in the metal surfaces – an effect similar to the space-charge zones in semiconducting elements used in microelectronics. Surprisingly, the application of an external electrical signal provides control of the mechanical properties of the new material. Upon request, the strength of the material can be doubled. Alternatively, the material is most malleable in its weak and ductile state. Up to now these results have been confined to the laboratory, but the researchers are already envisaging applications. In principle, when subjected to stress, the material can even generate electrical signals itself, which in turn affect its mechanical properties. The material could thus spontaneously enhance its local strength in areas carrying enhanced load, thus preventing or even healing damage caused by cracking.

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