  We report on the electrostatic complexation between polyelectrolyte-neutral
copolymers and oppositely charged 6 nm-crystalline nanoparticles. For two
different dispersions of oxide nanoparticles, the electrostatic complexation
gives rise to the formation of stable nanoparticle clusters in the range 20 -
100 nm. It is found that inside the clusters, the particles are pasted together
by the polyelectrolyte blocks adsorbed on their surface. Cryo-transmission
electronic microscopy allows to visualize the clusters and to determine the
probability distributions functions in size and in aggregation number. The
comparison between light scattering and cryo-microscopy results suggests the
existence of a polymer brush around the clusters.
