Particle dynamics in magnetorheological suspensions using diffusing wave spectroscopy

Magnetorheological suspensions acquire dipole moments in an external magnetic field. Suspensions of these dipolar particles rapidly aggregate to form long chains. We use diffusing-wave spectroscopy (DWS) and density-matched superparamagnetic emulsion droplets to probe the short-wavelength motion of the chains. The measured particle displacements are independent of the magnitude of the dipolar interactions at short times, but characterized by a constrained, subdiffusive motion at long times that slows as the dipolar interactions are increased. Our observations show good qualitative agreement with Brownian dynamics simulations of dipolar chains.