  In this review, we address the issue of the electrostatic complexation
between charged-neutral diblock copolymers and oppositely charged nanocolloids.
We show that nanocolloids such as surfactant micelles and iron oxide magnetic
nanoparticles share similar properties when mixed with charged-neutral
diblocks. Above a critical charge ratio, core-shell hierarchical structures
form spontaneously under direct mixing conditions. The core-shell structures
are identified by a combination of small-angle scattering techniques and
transmission electron microscopy. The formation of multi-level objects is
driven by the electrostatic attraction between opposite charges and by the
release of the condensed counterions. Alternative mixing processes inspired
from molecular biology are also described. The protocols applied here consist
in screening the electrostatic interactions of the mixed dispersions, and then
removing the salt progressively as example by dialysis. With these techniques,
the oppositely charged species are intimately mixed before they can interact,
and their association is monitored by the desalting kinetics. As a result,
sphere- and rod-like aggregates with remarkable superparamagnetic and stability
properties are obtained. These findings are discussed in the light of a new
paradigm which deals with the possibility to use inorganic nanoparticles as
building blocks for the design and fabrication of supracolloidal assemblies
with enhanced functionalities.
