Nanostructure Materials Magnetic Nanofluids Properties and Some Applications

Magnetic nanofluids (known also as ferrofluids or magnetic fluids) are a special category of smart nanomaterials, in particular magnetically controllable nanofluids [1]. These types of nanofluids are colloids of magnetic nanoparticles, such as Fe3O4, γ-Fe2O3, CoFe2O4, Co, Fe or Fe-C, stably dispersed in a carrier liquid [2]. Consequently, these nanomaterials manifest simultaneously fluid and magnetic properties. Macroscopically, the introduction of magnetic forces into the fundamental hydrodynamic equations for the quasihomogeneous magnetizable liquid medium gives rise to the magnetohydrodynamics of magnetic nanofluids, known also as ferrohydrodynamics and opens up an entire field of new phenomena [3] and promising applications [4]. From a microscopic point of view, long-range, attractive van der Waals and magnetic forces are ubiquitous and therefore must be balanced by Coulombic, steric or other interactions to control the colloidal stability of dispersed nanoparticle system, even in intense and strongly non-uniform magnetic field, specific to most of the applications [5,6]. Many of the envisaged applications, e.g., rotating seals or bearings, require magnetic fluids with high magnetization and at the same time, with long-term colloidal stability. These requirements are difficult to fulfill simultaneously and