Ultra-soft, liquid magnetic droplets could vault technology forward

UMass Amherst, California and Beijing researchers say magnetic field control of floating drops, like Harry Potter’s wand, not magic anymore

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Credit: Berkeley National Lab/Xubo Liu

AMHERST, Mass. – Conventional magnets are hard and rigid but have made great contributions to society and to modern industry, says materials scientist Thomas Russell of the University of Massachusetts Amherst. But this award-winning innovator dreamed of more – what if magnets could be soft, flowable as liquid and malleable to conform to a limited space?

In an article in this week’s Science, he and first author Xubo Liu from Beijing University of Chemical Technology, with others at Lawrence Berkeley National Laboratory and the University of California, Berkeley, report on a simple way they developed to transform paramagnetic ferrofluids – plain metal particles in suspension – into a magnetic state. The new ferromagnetic liquid droplets “represent a milestone for the further development of magnetic materials,” Russell says.

This means that by applying an external magnetic field, scientists can control liquid devices made this way, like waving Harry Potter’s wand, he suggests, “which opens promising research and application areas such as liquid actuators, liquid robotics and active-matter delivery.”

As the polymer scientist explains, he, Liu and the team used iron oxide nanoparticles in a special oil-polymer mixture to transform paramagnetic ferrofluid into the ferromagnetic state at room temperature. Because of nanoparticle-polymer mix interactions, the resulting ultra-soft droplet has magnetic properties similar to solid magnets but with liquid characteristics.

At nano scale, traditional ferromagnetic materials become magnetic only in the presence of a magnetic field. Based on these special physical properties, ferrofluids are already used in electrical devices, medical applications, mechanical engineering and materials science research, he notes.

Russell, who is also a visiting professor at the Berkeley National Lab, adds that the technique extends scientific knowledge of magnetic materials, and should encourage research into the deep-seated mechanism of how liquid magnets form. “This will facilitate the development of relative advanced instruments and new material theories,” he predicts. “These amazing liquid magnetic materials will attract attention in biology, physics and chemistry.”

A thousand years ago, he reflects, European voyagers used compasses they made from magnetite dug from the Earth to explore and discover new continents. For centuries, people learned to build smart magnetic devices to improve quality of life. “Such jumps in science and technology are always followed by a sudden emergence of a new material or theory,” Russell notes.

He and colleagues hope that the new, reconfigurable ferromagnetic liquid droplets they describe will provide more such possibilities, such as magnetically actuated liquid robotics, liquid vessels for delivering active matter and information technology with programmable liquid droplet patterns.

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This work was supported by the U.S. Department of Energy, the Office of Science at Lawrence Berkeley National Lab including Molecular Foundry and National Center for Electron Microscopy, the Beijing National Science Foundation, the Beijing Advanced Innovation Center for Soft Matter Science and Engineering at Beijing University of Chemical Technology and the China Scholarship Council.

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