1. Ferrofluids

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

3. 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

4. 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

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

6. 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.

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

8. 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

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