PARTICLE DYNAMICS IN MAGNETORHEOLOGICAL SUSPENSIONS USING DIFFUSING WAVE SPECTROSCOPY

Magnetorheological suspensions acquire dipole moments in an external m agnetic field. Suspensions of these dipolar particles rapidly aggregat e to form long chains. We use diffusing-wave spectroscopy (DWS) and de nsity-matched superparamagnetic emulsion droplets to probe the short-w avelength motion of the chains. The measured particle displacements ar e independent of the magnitude of the dipolar interactions at short ti mes, but characterized by a constrained, subdiffusive motion at long t imes that slows as the dipolar interactions are increased. Our observa tions show good qualitative agreement with Brownian dynamics simulatio ns of dipolar chains.