A comparison of the magnetorheology of two ferrofluids with different magnetic field-dependent chaining behavior

The effect of magnetic field-induced particle chaining on the magnetorheology of commercial iron oxide-based ferrofluids was investigated by comparison of a ferrofluid with particles that resist chaining and a ferrofluid with particles that interact when a field is applied, forming chain-like aggregates. This difference between the two ferrofluids was confirmed by optical microscopy and dynamic light scattering in an applied magnetic field. Both fluids had similar magnetic particle fraction, but showed different magnetorheological behavior. Chaining resulted in a stronger magnetic field-dependent viscosity enhancement and the appearance of an elastic modulus. The magnetorheology of these two fluids was described using the Mason number (Mn), resulting in two distinct Mn power law slopes at intermediate and small Mn values for the ferrofluid with magnetic field-induced aggregation. The commonly used magnetic coupling parameter failed to distinguish the behavior of the two ferrofluids.