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Ferrofluids

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Ferrofluids: Magnetic Liquids Liquid That Responds to a Magnetic Field = Colloidal Suspension of Superparamagnetic Magnetic Material

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Berger, P.; Adelman, N. B.; Beckman, K. J.; Campbell, D. J.; Ellis, A. B.; Lisensky, G. C. Journal of Chemical Education 1999, 76, 943-8. How Does A Magnetic Liquid Work? Electrostatic Repulsion 2FeCl 3 + FeCl 2 + 8NH 3 + 4H 2 O Fe 3 O 4 + 8NH 4 Cl Tetramethylammonium Cation (NH 4 + ) Hydroxide Anion (OH - ) ~ 10nm

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Synthesis of Magnetite Nanocrystals FeCl 3 + 3NH 4 OH FeO(OH) + 3NH 4 Cl + H 2 O 2FeO(OH) + Fe(OH) 2 Fe 3 O 4 + 2H 2 O Processes: 1) Nucleation 2) Growth 3) Termination + + + + + + + + + + + + + + + + + + + FeCl 2 + 2NH 4 OH Fe(OH) 2 + 2NH 4 Cl Fe(III) coordinates to 6 water molecules and Fe(II) coordinates to 4 water molecules (not shown) until the solid forms The water molecules on the periphery of the magnetite are ultimately replaced by tetramethylammonium hydroxide

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Unique Properties Stick to Magnets Take on 3-Dimensional Shape of a Magnetic Field Change Density in Proportion to Magnetic Field Strength

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Applications Inks money Biomedical attach drugs to magnetic particles, proposed artificial heart Damping speakers, graphic plotters, instrument gauges Seals gas lasers, motors, blowers, hard drives Berger, P.; Adelman, N. B.; Beckman, K. J.; Campbell, D. J.; Ellis, A. B.; Lisensky, G. C. Journal of Chemical Education 1999, 76, 943-8.

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Damping: Speakers See how a speaker works at: http://electronics.howstuffworks.com/speaker6.htm Rosensweig, R. E. Scientific American 1982, 247, 136-45.

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Damping: Rotating Shafts Ray, K.; Moskowitz, B.; Casciari, R. Journal of Magnetism and Magnetic Materials 1995, 149, 174-180. Cross-sectional view of a ferrofluid viscous inertia damper Energy band gap apparatus

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Seals Rosensweig, R. E. Scientific American 1982, 247, 136-45. VacuumAtmosphere Permanent Magnet Ferrofluid Rotating Shaft Magnetically Permeable Material

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