Reconfigurable ferromagnetic liquid droplets

• Published in: Science (American Association for the Advancement of Science) Vol. 365; no. 6450; pp. 264 - 267
• Main Authors: Liu, Xubo, Kent, Noah, Ceballos, Alejandro, Streubel, Robert, Jiang, Yufeng, Chai, Yu, Kim, Paul Y, Forth, Joe, Hellman, Frances, Shi, Shaowei, Wang, Dong, Helms, Brett A, Ashby, Paul D, Fischer, Peter, Russell, Thomas P
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 19-07-2019; AAAS
• Subjects: Coercivity; Crystals; Cylinders; Dipole interactions; Droplets; Ferrofluids; Ferromagnetic materials; Jamming; Magnetic dipoles; Magnetic fields; Magnetic properties; Magnetism; Magnetite; Magnetization; MATERIALS SCIENCE; Mud-water interfaces; Nanoparticles; Reconfiguration
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aaw8719

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.