Ferrofluids

Ferrofluids are part of a new kind of magnetic materials. These ferrofluids are made up from nanoparticles in a colloidal solution that stabilize the sample. These ferrofluids are of great technologic importance since one of the many applications available for them are as magnetic seal in motors, optic memory instruments, speakers and more.

The stabilization of the ferrofluids is accomplished by the covering of the magnetic particles with molecules of a large-chained surfactant. The surfactant is in charge of the entropic repulsion necessary to create a stable ferrofluid. 

The liquid phase on the colloidal solution is a determinant on the properties of the solution as shown in this paper.

The first step for the preparation of ferrofluids is the proper preparation of magnetite nanoparticles through a process of chemical reduction. Once the nanoparticles were synthetized, cleaned and properly dried two different processed were followed to form a ferrofluid.

One process included the addition of oleic acid and oil to the nanoparticles resulting in the formation of a mass that presented characteristics of a ferrofluid such as the magnetic properties. All the solution reacted to a magnet. This solution also presented properties of a colloid such as the Brownsted effect visible by the suspended particles.

The other process was the addition of tetramethylammonium hydroxide. Although a colloid was formed, this colloid didn’t exhibit the properties of a ferrofluid since a magnet could separate the phases present on the colloid.

The difference between both solutions was only the solute, the presence of oleic acid made the sample more stable and functioned as a emulsifying agent for that particular solution while on the other solution the mixture seemed homogeneous but was easily separated by the magnet.

The only requirement for a ferrofluid to function properly is the presence of any solution that can break the Vander-Waals interaction between the particles and the solvent so that the mixture is properly made and the ferrofluid presents magnetic properties without particle segregation.