FerrofluidsFerrofluids

Ferrofluids: Magnetic LiquidsFerrofluids: Magnetic Liquids

Liquid That Responds to a Magnetic Field

=

Colloidal Suspension of Superparamagnetic Magnetic Material

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 How Does A Magnetic Liquid Work?Work?

ElectrostaticRepulsion

2FeCl3 + FeCl2 + 8NH3 + 4H2O → Fe3O4 + 8NH4Cl

Tetramethylammonium Cation (NH4

+)

Hydroxide Anion (OH-)

~ 10nm

Synthesis of Magnetite NanocrystalsSynthesis of Magnetite NanocrystalsFeCl3 + 3NH4OH → FeO(OH) + 3NH4Cl + H2O

2FeO(OH) + Fe(OH)2 → Fe3O4 + 2H2O

Processes:1) Nucleation 2) Growth 3) Termination

→ →

+

++

+ +

+

++

+ +

+

+

+

+

+

++

+

+

FeCl2 + 2NH4OH → Fe(OH)2 + 2NH4Cl

• 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

Unique PropertiesUnique Properties

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

ApplicationsApplications• 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.

Damping: SpeakersDamping: Speakers

See how a speaker works at:http://electronics.howstuffworks.com/speaker6.htm

Rosensweig, R. E. Scientific American 1982, 247, 136-45.

Damping: Rotating Shafts 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

SealsSeals

Rosensweig, R. E. Scientific American 1982, 247, 136-45.

VacuumAtmosphere

Permanent Magnet

Ferrofluid

Rotating Shaft

MagneticallyPermeable Material