Ferrofluids magnetization

P 71 ] For fluid transport, ferrofluid magnetic displacement by using a commercial hydrocarbon-based ferrofluid was applied [159], This fluid is compatible with several aqueous dyed solutions. Miniature permanent magnets were used. 

Odenbach S. (Ed.), Ferrofluids Magnetically Controllable Fluids and Their Applications, Springer-Verlag New York, 2003. 

A ferrofluidic magnetic micropump was constmcted on a Si chip. Operation relies on the use of magnetically actuated plugs of ferroliquid (a suspension of nano-sized ferromagnetic particles), which is immiscible with the pumped fluid [301],... 

S. Odenbach, Ferrofluids, Magnetically Controllable Fluids and Their Appliccdions, Springer-Verlag, Berlin, 2002. 

Hatch A, Kamholz AE, Holman G, Yager P, Bohringer KF (2001) A ferrofluidic magnetic micropump. J Microelectromech Syst 10 215-221... 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

FIGURE 16.43 When a magnet is pulled up from this viscous ferrofluid, the particles of iron(lll) oxide align themselves with the magnetic field. Because strong attractions exist between the particles and the detergent molecules in the oil, the liquid is pulled into the field along with the particles. 

In recent years, the growing numbers of publications are concerned with ultra-fine metal oxide structures because of their useful applications as bactericides, adsorbents, energy storage media, magnetic data storage, and ferrofluids and specifically as catalysts [6, 7]. 

Gomes, J.D., Sousa, M.H., Tourinho, F.A. and Aquino, R. da Silva, G.J., Depeyrot, J., Dubois, E., Perzynski, R. (2008) Synthesis of core-shell ferrite nanopartides for ferrofluids chemical and magnetic analysis. Journal of Physical Chemistry C, 112 (16), 6220-6227. 

Ferrofluid NMR studies can also be used in order to determine geometrical and physical properties of the super-paramagnetic crystals, like their specific magnetization or radius. They also give valuable information on the aggregation level and on anisotropy. 

In TFB technique, the thin film radius is typically of the order of 100 pm, far larger than the contact film radius likely to be formed when two micron-sized droplets approach. The magnetic chaining technique overcomes this limitation, allowing the direct measurement of force-distance profiles between liquid colloidal droplets. This technique exploits the properties of monodisperse ferrofluid... 

Figure 2.25. Optical micrographs of a ferrofluid oil-in-water emulsion stabilized by 0.04 wt% BLG. The bar corresponds to 10 am. (a) On field corresponding to force of 1 pN. (b) 30 min after switching off the magnetic field. (Reproduced from [87], with...

Figure 7.1. (a) Transmission electron microscopy image of a collection of 200-nm magnetic emulsion droplets obtained from emulsifying an octane-based ferrofluid. (b) One droplet is shown after polymerization. A polymer shell is visible that encapsulates the iron oxide nanoparticles. (With permission of Ademtech). 

The Hamiltonian of a single isolated nanoparticle consists of the magnetic anisotropy (which creates preferential directions of the magnetic moment orientation) and the Zeeman energy (which is the interaction energy between the magnetic moment and an external field). In the ensembles, the nanoparticles are supposed to be well separated by a nonconductive medium [i.e., a ferrofluid in which the particles are coated with a surfactant (surface-active agent)]. The... 

For systems with parallel axes (e.g., single crystals of magnetic molecular clusters or a ferrofluid frozen in a strong field), the coefficients for the longitudinal response read... 

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