Ferrofluids are the world's first succesful nano-technology. First invented by R. E. Rosensweig in the early 1960's, these remarkable fluids are a continuous suspension of permanent nano-magnets. Synthesized by either chemical or physical processes, Ferrofluids can either be an aqeuous or organic suspension of magnetite, maghemite, and other hard magnetic materials. Current applications included liquid rotary o-rings for hard disc drives and vacuum systems, as well as voice coil coolants. Ferrofluids are researched here at HML for their applications in microfluidics and nano-liquid technology. The limitations of micro-fabrication can be avoided throigh the use of magnetic liquid micro-pumps, valves and other fluidic control hardware. The dificulty actually lies within the creation of the magnetic field. To that end, much NNF research is devoted to low-power, coil-less magnetic field generators.
By clicking on the picture, you can watch a video of a Ferrofluid puddle undergoing a normal field instability that is induced by magnets below the petri dish. The magnets are moved upwards to the dish at a slow enough rate so that the instability peaks can be seen as they form. The inter-peak spacing is approximately given by the Taylor wave-length for regular hydrodynamic instabilities, but the peak amplitude is a function of field intensity. Notice that as the magnets get closer, there is a change in the peak distribution from a hexagonal to square array. As the name implies, this instability is induced by the existence of a mgnetic field that is normal to the fluid surface. The field intensity ranges from zero (quiescent pool) to about .3T at the end of the movie. For more information on the NNF research conerning Ferrofluids, please contact Stephen Samouhos.