Ferrofluide

Ferrofluid, also known as ferrofluide in French, is a stable colloidal suspension of magnetic nanoparticles in a carrier liquid. The particles are typically about 10 nanometers in diameter and consist mainly of magnetite (Fe3O4) or maghemite (gamma-Fe2O3). Each particle is coated with a surfactant or polymer layer to prevent agglomeration, enabling the suspension to remain fluid under normal conditions.

In the absence of a magnetic field, the fluid behaves like a conventional oil or water-based liquid. When exposed to a magnetic field, the particles align with the field, imparting magnetization to the fluid and causing it to form spiky, branching surface structures near magnets. This field-responsive behavior makes ferrofluids useful for demonstrations and certain mechanical applications. The fluid’s apparent viscosity can also change in a magnetic field, a phenomenon known as magnetoviscosity.

Fabrication: Ferrofluids are produced by synthesizing magnetic nanoparticles and dispersing them in a carrier liquid with surface-active agents. Common carriers include mineral oil, silicone oil, or water-based solutions, selected for compatibility with the intended application.

Applications: Ferrofluids are used in rotary seals and dampers, in loudspeakers for damping and cooling, in microfluidic devices, and in laboratory demonstrations and artistic displays. They are also investigated for medical and industrial uses, such as targeted delivery under magnetic fields and cooling or lubrication in electronics.

History and safety: Ferrofluid was developed in the 1960s by Steve Papell at NASA for use as a liquid seal in rotating machinery. It is generally handled as a chemical with standard precautions for oils or solvents; it should not be ingested and may stain surfaces.