Blue green droplet hits the surface of a liquid

Liquid robots, dancing droplets—the future of magnets

UMass distinguished professor develops first ever liquid magnet 

July 23, 2019

Thousands of years ago, societies around the globe began to study and utilize magnetic iron oxide. Placed in a bowl of water, these magnets became compasses that guided humans to explore the planet further. For centuries, people learned how to use the magnets to build various smart devices to improve the quality of life and advance our understanding of the world.  


After all this time, one thing has always remained constant: Our magnets have been made from solid, rigid materials.  

But Thomas RussellPolymer Science and Engineering,  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. It’s not magic anymore; it’s reality now. 

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.” 

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. 

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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