Dynamical structure and viscosity of dilute magnetorheological suspensions under perturbation

Dilute magnetorheological suspensions in the presence of a static field exhibit a power law behavior as a function of time in some of their rheological properties. We have found that strong changes occur in the viscosity of these complex fluids when, in addition to a static field, they are exposed to a magnetic perturbation. The effects of a sinusoidal perturbation on the long-time viscosity are analyzed and discussed on the basis of our observations by optical microscopy of the pattern formation. The perturbation generates an additional kinetic mechanism that considerably enhances the lateral aggregation of the chains formed by the application of the static field, yielding higher values of the viscosity. The role of the particle concentration as well as the characteristics of the perturbation and the simultaneity of the application of the fields is here investigated.