Ferrofluid

Contents

CCA!
A magnet placed just below a dish containing ferrofluid generates an array of spikes in the fluid.
Magnetite, Fe3O4 is a ferrimagnetic substance containing both Fe2+ and Fe3+ ions. As in ferromagnetic substances, the unpaired electrons in ferrimagnetic substances are aligned in large domains. However, in ferrimagnetic substances some of the spin sets are opposed to others (this depends on the position of the Fe2+ and Fe3+ ions in the crystal lattice). Since more of the spins are aligned in one direction than in another, the spins do not cancel. A magnet will attract a ferrimagnetic substance.

micellesIn the ferrofluid, tiny particles of magnetite are suspended throughout the liquid medium. In order to prevent the particles from aggregating, they are surrounded by the polar end of long chain fatty acid molecules, to which they are attracted by ion-dipole forces. (See the diagram at the right.) The long, nonpolar tails of the molecules are attracted by London forces to the molecules of the oil that serves as the liquid medium, but cannot compete with the polar ends in their attraction for the Fe3O4 particles. These structures bear a certain resemblance to the micelles formed by soaps and detergents. However, in the case of soaps, the nonpolar tails are directed toward the interior, where they surround water-insoluble oils, while the polar ends (-COO- or -SO3- groups) are strongly attracted to water molecules by ion-dipole forces.

Safety/Precautions

Ferrofluid is very difficult to clean up.

Journal of Chemical Education is a publication of the Division of Chemical Education, Inc. of the American Chemical Society.