Enhanced rheological properties of dilute suspensions of magnetic nanoparticles in a concentrated amphiphilic surfactant solution

We present an experimental study of the magnetorheological response of dilute suspensions of magnetic nanoparticles in concentrated amphiphilic surfactant solutions. Low particle content (<0.4% v/v) induced significant increase in viscosity, enhancing the shear thinning behavior observed in the absence of the nanoparticles. A magnetic field induced yield stress of up to 10 Pa at magnetic fields of up to 0.4 T was also observed. Experiments under small amplitude oscillatory shear indicate a transition from viscous to elastic behavior at a critical magnetic field which depends on the frequency of the oscillatory shear. At low applied magnetic fields loss and storage moduli are independent of the magnetic field and increase with the frequency of the oscillatory shear. At high applied magnetic fields both the loss and storage moduli seem to asymptote to a power law dependence on the magnetic field magnitude. These results illustrate the possibility of inducing dramatic changes in the rheological properties of complex fluids by addition of minute amounts of magnetic nanoparticles and application of magnetic fields.