Ferrofluids are composed of three basic components, a) sub-microscopic, magnetically permeable particles of iron oxide, usually magnetite, b) a surfactant or dispersant coating and c) a carrier fluid.
The surfactants are soap-like materials that work to coat the particles and keep them from being attracted to each other. The carrier fluid may be water or oil, and will help to determine the over-all viscosity, or thickness of the ferrofluid.
The concentration of particles in a ferrofluid also contributes to the viscosity, but since this value is typically low, the nature of the carrier fluid has the greatest influence. The particle concentration also determines the “Saturation Magnetization” (Ms) of the fluid, or the degree to which it is attracted to a magnet. Ferrofluids are not magnetically attractive in themselves, they must be in a magnetic field in order to behave as one magnet.