Pattern formation in spin-coating of hybrid colloids in different magnetic field configurations

Abstract

We report experimental results on the patterns that are formed during spin-coating of magnetic colloids at moderate concentrations and compare them with results obtained in diluted colloids. We show that, for moderate concentrations, the magnetic interaction between the (ferro)magnetic particles and with the external field is strong enough to overcome the centrifugal force. We study two different configurations for the magnetic field. The first one consists on an axial uniform field, where we obtain spikes perpendicular to the substrate with a well defined order which decreases as rotation rate increases. The second one consists on a radial non-uniform field, where we obtain elongated deposits radially disposed on the substrate. The effect of magnetic fields at moderate concentrations on the effective viscosity is confirmed to be much more important in the case of a uniform magnetic field, by increasing the hydrodynamic timescale which gives the ferromagnetic particles enough time to strongly interact to form the spikes.

Toward ultra-low homogeneous magnetic field generation: space-efficient coil configurations based on the MSR

“…Traditional coil configurations (without MSR) for homogeneous magnetic field generation have been widely studied and used in spin-coating of magnetic colloids, biomedical experiments and ferromagnetic nanoparticles transport [18][19][20]. The most commonly used square configurations are Helmholtz two-coil, Merritt three-coil and Merritt four-coil [21,22].…”