Retention of Paramagnetic Particles by Magnetite Particle Clusters with Multifunctional Character

Abstract

ABSTRACTThe magnetic force exerted by a 3-D array of five hundred identical magnetite particles (with rm = 400 nm) on two differently sized paramagnetic particles (with rp = 160 and 1000 nm) was investigated to reveal the multifunctional character of magnetic particle clusters that may prove to be advantageous when used as a HGMS element. The orientation of the magnetic field, the separation s between the magnetite particles in the array, and the distance h between the paramagnetic particle and the surface of the magnetite array were all found to have significant effects. Both the large and small paramagnetic particles experienced interactions with the array that were strictly due to the array behaving collectively as a single magnetic unit; but these relatively “smooth” interactions were much longer-ranged for the large paramagnetic particle. The large and small paramagnetic particles also experienced interactions with the array that were strictly due to individual (yet cooperative) interactions with each of the magnetite particles in the array; but in most cases these individual and relatively “rough” interactions were short-ranged for both paramagnetic particles. The spatial range of these solitary (multifunctional) interactions depended markedly on the values of h and s, and especially rp, as did the regions where these collective and individual interactions overlapped. The orientation of the magnetic field produced maximum and bounding interactions when α = 0° and α = 90°, with the resulting repulsive interactions at α = 0° (with Ha parallel to the surface of the array) always being less than the resulting attractive interactions at α = 90° (with Ha perpendicular). As a HGMS element, this unique multifunctional character of magnetite particle clusters could give various forms of supported magnetite a key advantage over traditional stainless steel wool for retaining both large and especially small paramagnetic particles of weak magnetic character.