Orientational Brownian motion in a viscoelastic medium

A model has been proposed for the complete (2D) orientational Brownian motion of axially symmetric particles in a Kelvin viscoelastic medium. It has been shown that the elastic response of the carrier medium can be correctly determined by introducing an additional variable, the moment elastic forces, which, together with the particle-orientation vector, composes the complete set of phase variables of a system. A set of stochastic equations (Langevin equations) has been derived for these values. This set has been employed to construct, under the effective field approximation, a simple set of moment equations describing the magnetization dynamics of a ferrogel, i.e., a dispersion of single-domain nanoparticles in a gel matrix. The theoretical results qualitatively agree with the data of magnetic microrheology of gelatin-based ferrogels.