The Soft Matter Science and Engineering Advanced Innovation Center at Beijing University of Chemical Technology recently announced that researchers at the university have discovered a new magnetic material in collaboration with teams from Lawrence Berkeley National Laboratory and other institutions in the United States. By controlling the self-assembly of magnetic nanoparticles in the water and oil interface, the ferromagnetic fluid was successfully transformed from paramagnetism to ferromagnetism. Generally speaking, a magnet is no longer necessarily a hard solid, but can also be a moving liquid.
According to reports, from household appliances such as refrigerators to space equipment such as magnetic navigators, solid magnetic materials appear everywhere. However, common liquid magnetic materials, such as traditional ferromagnetic fluids, have flexible forms but do not have magnetic poles themselves. Only when magnetized by external magnetic field can they show specific magnetism. The ferromagnetic droplets or liquid magnets found in the study combine both the magnetism of a solid magnet and the fluidity of a liquid to form a new kind of magnetic soft material.
The researchers mixed water-based magneto-fluid materials with organic matter, and the carboxylated ferroferric oxide magnetic nanoparticles dispersed in the aqueous phase interact with the amino cage-shaped silsesquioxane dissolved in the adjacent oil phase at the water-oil interface, then the magnetic nanoparticle surfactant is formed through situ self-assembly to adsorb to the interface and realize blocking phase transition, forming ferromagnetic droplets. The hysteresis loop of the droplet was measured at room temperature, and it was found that, different from the traditional paramagnetic magnetic fluid, the droplet showed a certain strength of remanence and coerce that can be converted to ferromagnetism. Combined with the latest all-liquid 3D printing and microfluidic molding technologies, researchers can manufacture magnetic liquid devices of arbitrary morphology in all-liquid conditions.
In addition, the formed liquid can be reconstructed by changing the acid-base environment in the liquid to realize reversible magnetization or demagnetization. This new magnetic material has many strange properties, and it is expected to be used in magnetic-controlled liquid robots, programmable liquid microreactors and other fields in the future as well as to promote the development of new liquid magnetic material characterization technology such as polarizing neutron magnetic field imaging.