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.

• Received 12 May 1998

DOI:https://doi.org/10.1103/PhysRevE.58.3372