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Séminaire 1.10.2014 à 11h

par Guillaume Mériguet - 18 septembre 2014

Petr Melenev (I.C.M.M. Perm - Russie), présentera un séminaire le 1er Octobre 2014 à 11h00 dans la bibliothèque du laboratoire PHENIX (7e étage, bâtiment F, porte 754) intitulé :

Molecular dynamics simulation of the ensembles of magnetic nano- and microparticles


Method of Molecular Dynamics (MD) is used for simulations of two types of polymer composites filled with magnetoactive particles. In the first case, ferromagnetic nanoparticles are embedded in a soft polymer network. The mechanical behavior of such a composite under an external field is largely determined by the balance between the Zeeman and inter-particle magnetic energy (the particle magnetic anisotropy is taken into account) and the elasticity of polymer chains. The second type of the simulated system imitates a magnetorheological fluid that is a dispersion of a micron-size magnetic powder, e.g. carbonyl iron. In this case, the particles are magnetically soft, i.e., both the directions and magnitudes of their magnetic moments depend on the applied field. We consider the particles with zero remanent magnetization in a relatively weak external field, which allows us to use the linear polarization assumption. The modeled particles, being multidomain, are magnetized non-homogenously that at short interparticle distances entails substantial deviation of the inter-particle magnetic interaction from that of point dipoles. Given that, a rigorous micromagnetic simulation of an ensemble with a large number of particles is immensely laborious. As an attempt to circumvent this difficulty, we use an approximate description of the pair interaction of magnetizable particles and the hypothesis of additivity of these interactions. The corresponding simulations show that the particles tend to form oblate clusters. This shape is qualitatively different from both the chain and column patterns encountered in simulations of the point dipole particles. The work is performed with the aid of the ESPResSo package, a flexible and powerful open-source software developed by the international team of researches and oriented to MD- based calculations in polymer science, polyelectrolyte physics, bio-physics and various other fields of natural science.