Rigid, superparamagnetic chains of permanently linked beads coated with magnetic nanoparticles. Synthesis and rotational dynamics under applied magnetic fields.

An inexpensive and versatile approach is reported for the synthesis of monodisperse magnetoresponsive rods of desired diameter, length, and magnetic susceptibility based on the confined alignment of magnetic beads in microchannels of selected channel height, followed by localized hydrolysis of sol-gel precursors within polyelectrolyte shells adsorbed on the beads. The layer-by-layer technique was used to coat the polystyrene beads with polyelectrolytes of alternating charge and with charged magnetic nanoparticles, and the polystyrene cores could be removed either by solvent dissolution or by calcination to form hollow-shelled chains. The reorientation dynamics of single and clustered chains following the application of an external magnetic field was evaluated theoretically, with favorable comparisons with the experimental data.