title: Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields.
abstract: When a micron-sized magnetizable particle is introduced into a suspension of nanosized magnetic particles, the nanoparticles accumulate around the microparticle and form thick anisotropic clouds extended in the direction of the applied magnetic field. This phenomenon promotes colloidal stabilization of bimodal magnetic suspensions and allows efficient magnetic separation of nanoparticles used in bioanalysis and water purification. In the present work, the size and shape of nanoparticle clouds under the simultaneous action of an external uniform magnetic field and the flow have been studied in detail. In experiments, a dilute suspension of iron oxide nanoclusters (of a mean diameter of 60 nm) was pushed through a thin slit channel with the nickel microspheres (of a mean diameter of 50 μm) attached to the channel wall. The behavior of nanocluster clouds was observed in the steady state using an optical microscope. In the presence of strong enough flow, the size of the clouds monotonically decreases with increasing flow speed in both longitudinal and transverse magnetic fields. This is qualitatively explained by enhancement of hydrodynamic forces washing the nanoclusters away from the clouds. In the longitudinal field, the flow induces asymmetry of the front and the back clouds. To explain the flow and the field effects on the clouds, we have developed a simple model based on the balance of the stresses and particle fluxes on the cloud surface. This model, applied to the case of the magnetic field parallel to the flow, captures reasonably well the flow effect on the size and shape of the cloud and reveals that the only dimensionless parameter governing the cloud size is the ratio of hydrodynamic-to-magnetic forces-the Mason number. At strong magnetic interactions considered in the present work (dipolar coupling parameter α≥2), the Brownian motion seems not to affect the cloud behavior.
authors.affiliation: University of Nice-Sophia Antipolis, CNRS, Laboratory of Condensed Matter Physics, UMR 7336, 28 avenue Joseph Vallot, 06100 Nice, France.
authors.forename: C
authors.initials: C
authors.lastname: Magnet
authors.affiliation: University of Nice-Sophia Antipolis, CNRS, Laboratory of Condensed Matter Physics, UMR 7336, 28 avenue Joseph Vallot, 06100 Nice, France.
authors.forename: P
authors.initials: P
authors.lastname: Kuzhir
authors.affiliation: University of Nice-Sophia Antipolis, CNRS, Laboratory of Condensed Matter Physics, UMR 7336, 28 avenue Joseph Vallot, 06100 Nice, France.
authors.forename: G
authors.initials: G
authors.lastname: Bossis
authors.affiliation: University of Nice-Sophia Antipolis, CNRS, Laboratory of Condensed Matter Physics, UMR 7336, 28 avenue Joseph Vallot, 06100 Nice, France.
authors.forename: A
authors.initials: A
authors.lastname: Meunier
authors.affiliation: University of Nice-Sophia Antipolis, CNRS, Laboratory of Condensed Matter Physics, UMR 7336, 28 avenue Joseph Vallot, 06100 Nice, France.
authors.forename: S
authors.initials: S
authors.lastname: Nave
authors.affiliation: Department of Mathematical Physics, Ural Federal University, 51 Prospekt Lenina, Ekaterinburg 620083, Russia.
authors.forename: A
authors.initials: A
authors.lastname: Zubarev
authors.affiliation: University of Nice-Sophia Antipolis, Laboratory ECOMERS (Ecosystèmes Côtiers Marins et Réponses aux Stress), EA 4228, 28 avenue Valrose, 06108 Nice Cedex 2, France.
authors.forename: C
authors.initials: C
authors.lastname: Lomenech
authors.affiliation: Belarusian National Technical University, UNESCO Department "Energy Conservation and Renewable Energies", 65 Prospekt Nezavisimosti, 220013 Minsk, Belarus.
authors.forename: V
authors.initials: V
authors.lastname: Bashtovoi
mesh_terms: D003102:Colloids / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D060526:Magnetic Fields; D058185:Magnetite Nanoparticles / Q000737:chemistry* / Q000528:radiation effects*; D008863:Microspheres; D008956:Models, Chemical
chemical_list: D003102:Colloids; D058185:Magnetite Nanoparticles