In the past decade, colloidal solutions have been assumed to be very efficient templates for controlling particle size and shape. A large number of groups have used reverse micelles to control the size of spherical nanoparticles. This makes it possible to determine the various parameters involved in such processes, and demonstrates that nanoparticles can be considered to be efficient nanoreactors. However, some discrepancies arise. There are few reports concerning the control of particle shape, and it is still rather difficult to determine the key parameters, such as the adsorption of salts and other molecules, and the synthesis procedure. Here, we discuss these controls of the size and shape of inorganic nanomaterials.

In this feature article, syntheses of nanosized particles by using colloidal assemblies as a template are described. We asked ourselves the following question: What parameters play a role in the control of the size, shape, and polydispersity? We know that parameters such as the shape of colloidal assemblies, the hydration of the head polar group, the water molecules bounded to the interface, etc. play a major role. However, there are a number of exceptions preventing any generalization. It is shown that the chemical mechanism in nanoparticles production in colloidal assemblies can differ from those usually observed in homogeneous solution. This shows that the solution chemistry cannot always be transferred to colloidal systems. It is possible to select the size and markedly reduce the polydispersity by a surface treatment of the nanoparticles. This favors formation of mono-and multilayers made of nanoparticles, and it is found that these particles form crystals organized in a three-dimensional face-centered cubic superlattice.

In this feature article, the methods of obtaining various mesostructures made of nanocrystals are described. With silver and silver sulfide, the nanocrystals are able to self organize in 2D and 3D super lattices to form “supra” crystals. With cobalt and ferrites nanocrystals, it has been possible to make ribbons, dots, or labyrinths. These mesostructures present new physical properties differing from those of the isolated nanocrystal and from those of the bulk phase. Collective optical, magnetic, and transport properties are demonstrated. By applying a magnetic field during the deposition process of nanocrystals, the easy axes of the particles are oriented along the direction of the applied field, inducing again the collective magnetic properties.