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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: SYMPOSIUM Driven Soft Matter III

CPP 18.7: Talk

Tuesday, February 26, 2008, 18:15–18:30, C 130

Dynamical properties of magnetic nanoparticles in ferrofluids investigated by Brownian dynamics — Guillaume Meriguet¹, •Marie Jardat¹, Emmanuelle Dubois¹, Vincent Dupuis¹, Bela Farago², Regine Perzynski¹, and Pierre Turq¹ — ¹Universite Pierre et Marie Curie-Paris6, Paris, France — ²Institut Laue Langevin, Grenoble, France

The dynamical properties of real ferrofluids, charge-stabilized aqueous dispersions of magnetic particles bearing a permanent dipole, are investigated with and without an external magnetic field by Brownian dynamics simulations. On the one hand, since the magnetic particles have an anisotropic optical index, their rotational properties have been studied experimentally: an external magnetic field induces a macroscopic birefringence the relaxation of which is followed after the magnetic field is suppressed. A non-equilibrium simulation procedure is proposed that mimics the experimental operating mode: after equilibrium simulations under magnetic field, the birefringence decay is recorded once the field is suppressed. On the other hand, the translational dynamics of the nanoparticles is investigated. The diffusion coefficient of the particles has been experimentally determined at several wave-vectors using neutron spin echo spectroscopy, with and without an external magnetic field. The same quantities are computed from Brownian dynamics simulations. The comparison between experimental and theoretical results allow us to evaluate the influence of several factors on the dynamics, such as the volume fraction, the dipolar interactions or hydrodynamic interactions.