Magnetophoresis of colloidal particles in a dispersion of superparamagnetic nanoparticles: theory and experiments

Recent works have demonstrated the exciting possibility of inducing a tunable magnetic behavior in non-magnetic colloids by immersing them in a dispersion of superparamagnetic nanoparticles (NPs). Here we show experimentally that non-magnetic latex particles in a dispersion of superparamagnetic NPs experience a nontrivial, two-step "go and come-back" motion when brought under a uniform magnetic gradient. Our theoretical analysis indicates that the observed motion is due to the combined effect of the behavior of latex particles as magnetic holes and the adsorption of NPs at the latex surface. In agreement with theory, the NPs adsorption has been confirmed in our experiments by three independent experimental techniques (EDS, SEM and electrophoresis).