CHAPTER 2: Magnetorheology of Fe Nanofibers Dispersed in a Carrier Fluid

Nanofiber-based magnetorheological (MR) fluids display an increased achievable yield stress and greatly reduced sedimentation as compared to conventional MR fluids which typically consist of micron-sized spherical ferromagnetic particles suspended in a carrier fluid. The maximum achievable yield stress of nanofiber-based MR fluids can be more than double that of MR fluids that contain strictly spherical particles at the same particle loadings. Conventional MR fluids display appreciable settling whereas the nanofiber-based fluids display no discernible settling at volume fractions greater than ∼6 vol%. However, a maximum volume fraction of <10 vol% is achievable in suspensions containing only nanofibers. To achieve the higher loadings required for most commercial applications, dimorphic MR fluids were created in which spherical particles are partially substituted with nanofibers. Dimorphic MR fluid display significantly enhanced particle sedimentation properties with yield stresses equivalent to or greater than those of conventional MR fluids. Nanofibers are well suited as model particles for the systematic experimental and theoretical study of the shape- and composition-dependent properties of MR fluids owing to their well-defined geometry, controllable dimensions and composition. The use of nanofibers has greatly enhanced MR fluid properties and has resulted in a better understanding of their physical behavior.