Ferrofluid composition, method of making, and apparatus and method using same

A stable ferrofluid composition and a method of preparing and using the ferrofluid composition, and a ferrofluid seal apparatus is described. The ferrofluid composition comprises a liquid carrier, ferromagnetic particles sufficient to provide magnetic properties to the ferrofluid dispersed in the liquid carrier and a dispersing amount of a cationic surfactant to provide a stable ferrofluid composition. The stable ferrofluid compositions have improved electrical conductivity and are useful, e. g. in sealing computer disc drives. Thus, an electrically conductive ferrofluid-film-bearing apparatus and seal apparatus (40) for a shaft (46) employs a low-viscosity, electrically conductive ferrofluid composition (62, 50) as an 0-ring seal and as a ferrofluid bearing surrounding shaft (46) which composition comprises a liquid carrier, and contains in combination an electrically conductive amount of a cationic surfactant and dispersed carbon particles, to obtain a low-electrical-resistivity ferrofluid having a low viscosity.