Magnetic fluid and nanoparticle applications to nanotechnology

Magnetic field based micro/nanoelectromechanical systems (MEMS/NEMS) devices are proposed that use 10 nm diameter magnetic particles, with and without a carrier fluid, for a new class of nanoduct flows, nanomotors, nanogenerators, nanopumps, nanoactuators, and other similar nanoscale devices. A few examples of macroscopic ferrohydrodynamic instabilities that result in patterns, lines, and structures are shown that can be scaled down to sub-micron dimensions. Background to magnetic fluid technology Present electric field based microelectromechanical system (MEMS) technology of solid capacitive structures can be extended to include magnetic field interactions with ferrofluids and submicron size magnetic particles for micro/nanoelectromechanical system (MEMS/NEMS) devices. Ferrofluids, which are synthesized as a stable colloidal suspension of permanently magnetized particles such as magnetite of 10 nm diameter, are an excellent choice for such NEMS magnetic field technology. Brownian motion keeps the 10 nm size particles from settling under gravity, and a surfactant is placed around each particle to provide short range steric repulsion between particles to prevent particle agglomeration in the presence of non-uniform magnetic fields (Rosensweig, 1985). Conventional ferrofluid applications use DC magnetic fields from permanent magnets for use as a liquid O-ring in rotary and exclusion seals, as dampers in stepper motors and shock absorbers, and for heat transfer in loudspeakers (Berkovsky & Bashtovoy, 1996). Almost every computer disk drive uses a magnetic fluid rotary seal for contaminant exclusion and the semiconductor industry uses silicon crystal growing furnaces that employ ferrofluid rotary shaft seals. Ferrofluids also have very interesting lines, patterns, and structures that can develop from ferrohydrodynamic instabilities as illustrated in Figures 1 and 2 for the ferrofluid peaking behavior resulting from a magnetic field perpendicular to the free surface of a ferrofluid layer; in Figure 3 for the gear-like structure resulting from the radial perpendicular field instability when a small magnet is placed behind a ferrofluid drop confined between closely spaced glass plates; and in Figures 4 and 5 for the labyrinth instability that results when a magnetic field is applied tangent to the thin dimension of a ferrofluid layer confined between closely spaced glass plates. All pictures use a ferrofluid with saturation magnetization of 400 G. In Figures 3–5 the ferrofluid is surrounded by a 50% propanol/ 50% deionized water mixture in order to prevent the ferrofluid from wetting the glass plates. These applications concern macroscopic systems but because the ferrofluid particles have a particle diameter of order 10 nm, there are also many potential new MEMS/NEMS applications using ferrofluid particles, with and without carrier fluid, for nanoduct flows, nanomotors, nanogenerators, nanopumps,