ABSTRACT
In nature, materials that exhibit magnetic properties are invariably solids. Magnetizable fluids, then, are not naturally occurring substances. In the case of ferrofluids, each particle of the solid phase is only a few nanometers in diameter. This chapter discusses two very different kinds of magnetic fluids that have found uses in engineering. These are ferrofluids and magnetorheological (MR) fluids. Unlike the nano-sized particles found in a colloidal ferrofluid, the particles in an MR fluid are several orders of magnitude larger. Unlike the nano-sized particles found in a colloidal ferrofluid, the particles in an MR fluid are several orders of magnitude larger. Ferrofluid is a magnetically responsive liquid. In principle, one has a wide choice of magnetic solids from which particles can be selected for ferrofluid synthesis. A wide variety of liquids can be used to make ferrofluids for different end use applications, limited primarily by the ability to select a compatible surfactant.
