  We report on the structural properties of mixed aggregates made from
rare-earth inorganic nanoparticles (radius 20 Angstroms) and
polyelectrolyte-neutral block copolymers in aqueous solutions. Using scattering
experiments and Monte Carlo simulations, we show that these mixed aggregates
have a hierarchical core-shell microstructure. The core is made of densely
packed nanoparticles and it is surrounded by a corona of neutral chains. This
microstructure results from a process of controlled association and confers to
the hybrid aggregates a remarkable colloidal stability.
