In the blockbuster terminator Franchised film, an evil robot is transformed into different forms and human objects and oozes through narrow openings, thanks to its composition in "liquid metal". Although current robots do not have these features, the technology is getting closer to the development of new liquid metals that can be manipulated in a 3D space with magnets. Reported in Applied materials and interfaces ACS, the materials could one day find applications in soft robotics. Watch them in action here.
Liquid metals at room temperature, such as gallium and certain alloys, have unique properties, including high conductivity, low melting point and high deformability. These properties make them attractive for use in soft robots and soft electronic components. By adding magnetic particles, such as nickel or iron, researchers can produce liquid metals that they can manipulate with magnets. However, due to their high surface tension, most magnetic liquid metals can only move horizontally and they must be completely immersed in the liquid to avoid forming a paste. Liang Hu, Jing Liu and their colleagues wanted to create a magnetic liquid metal that can be moved and stretched both horizontally and vertically, without the need to put the material completely in liquid.
To do this, the researchers first worked with the material immersed in a liquid. They added iron particles to a drop of an alloy of gallium, indium and tin immersed in hydrochloric acid. A layer of gallium oxide was formed on the surface of the droplets, which lowered the surface tension of the liquid metal. When the team applied two magnets in opposite directions, they could stretch the droplet to almost four times their rest length. They could also manipulate the liquid metal to connect two horizontal submerged electrodes and, because of its conductive properties, illuminate an LED bulb. The liquid metal could even stretch vertically then move horizontally to connect two electrodes – the highest exposed to the air and the lowest in the hydrochloric acid. This demonstrated that it was not necessary for the material to be completely immersed in a liquid. In this way, the researchers say that the magnetic liquid metal was reminiscent of a standing amphibian.
These authors acknowledge the funding of Project 111 and the National Natural Science Foundation of China.
The summary accompanying this study is available here.
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