(95h) Measurements of Torque and Flow in Magnetic Nanoparticle Suspensions (Ferrofluids)

Ferrofluids are a class of magnetically-active complex fluids consisting of suspensions of magnetic nanoparticles in Newtonian carrier fluids. We will report measurements of torque and flow in water- and kerosene-based ferrofluids in a uniform rotating magnetic field. We measured the torque needed to restrain a cylindrical spindle immersed in the fluid and to restrain a cylindrical container filled with the fluid. Preliminary results using a commercial magnetorheological (MR) fluid, consisting of iron micropartcles, will also be presented. Various geometric aspect ratios and fluid concentrations were used in order to test recently derived analytical theories for the flow of ferrofluids in these situations. Measurements of the velocity profiles of the ferrofluids in both situations were made using the Ultrasonic Velocity Profile method, which is ideally suited for opaque fluids such as ferrofluids. These measurements demonstrate that there is indeed a body-couple induced flow in these fluids.