Not all magnets have to be solids 鈥� a new kind of liquid magnet may eventually help control wireless soft robots.
Liquid magnets of a sort already exist. These聽ferrofluids are a mixture of a non-magnetic liquid and solid magnetic nanoparticles, but they only work when under the influence of an external magnetic field. Thomas Russell at the University of Massachusetts Amherst and his colleagues were able to turn a ferrofluid into a truly magnetic fluid that retains its magnetic properties.
They did this using magnetic nanoparticles containing iron oxide. When those particles float freely in liquid hydrocarbon, they create a ferrofluid, but Russell and his colleagues found that when there are enough of them to completely cover the surface of a droplet and jam together, the droplet stays magnetic.
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鈥淭he interior of these is fully liquid, particles are moving around inside, but they鈥檙e behaving just like a solid magnet,鈥� says Russell. 鈥淓very single particle in the droplet, whether it鈥檚 on the surface or in the interior, is contributing to the fluid鈥檚 magnetic field.鈥� The researchers aren鈥檛 yet sure why the interior nanoparticles remain magnetically coupled to the surface ones, he says.
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When exposed to magnetic fields, the droplets could move around or change their shape, and if the magnetic field聽rotated, the droplets spun too, which the researchers confirmed by dropping some dye into a pool of oil with the droplets and watching it swirl. This聽means they could eventually be used to move parts of soft robots. That would require an external magnetic field, but no wires or internal batteries.
鈥淚鈥檓 certain we can make magnetized grabbers,鈥� says Russell. 鈥淲e could even make little people out of liquids with magnetic arms that walk around.鈥�
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