Abstract
The attractive interactions between oppositely charged species (colloids, macromoleculesetc) dispersed in water are strong, and the direct mixing of solutions containing suchspecies generally yields a precipitation, or a phase separation. We have recently developedmeans to control the electrostatically driven attractions between nanoparticles andpolymers in water, and at the same time to preserve the stability of the dispersions. Wegive here an account of the formation of supracolloidal aggregates obtained by co-assemblyof 7 nm particles with copolymers. Nanostructured rods of length comprised between 5 and50 µm and diameter 500 nm were investigated. By application of a magnetic field, therods were found to reorient along with the magnetic field lines. The kinetics ofreorientation was investigated using step changes of the magnetic field of amplitudeπ/2. From the various results obtained, among which is an exponential decay of the tangent ofthe angle made between the rod and the field, we concluded that the rods aresuperparamagnetic.
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