Liquid Magnets

As early as the 1960s, scientists discovered that liquids could be magnetized, but only when they were exposed to a strong magnetic field. Recently, however, researchers have created a magnetic liquid that remains magnetized even when the external field is removed, opening up a host of new applications for fluidic devices.

The unique material was developed by injecting iron-oxide nanoparticles into droplets of toluene – a liquid hydrocarbon that is insoluble in water. A soap-like material was then added and the droplets were suspended in water, causing the nanoparticles to group together on the surface, forming a semisolid shell. When placed on a stirring plate with a bar magnet, the positive and negative poles of the liquid followed the solid magnet. But when the magnet was removed, the soapy emulsion enabled the droplets to maintain their magnetic charge.

Using a 3D printer, researchers then used two liquids (one containing nanoscale clay particles and one containing nanoscale polymer particles) to generate a fluidic device on a specially designed glass substrate. The two liquids quickly came together to create thin channels about one millimeter in diameter. Such fluidic circuits could serve a wide range of applications from automating chemical reactions to filtering out unwanted by-products in a functioning system.