One area of particular effort recently is the use of colloidal particles as precursors in engineering new materials. Nevertheless, these particles are nearly always spheres. This places limitations on the structures that can be built, especially in making photonic-bandgap materials. Therefore, it is a great challenge to create new colloids with an original shape, i.e. different from the sphere, in a controllable manner.

We present here an original approach to create organic-inorganic colloidal clusters with a perfect controlled shape. The synthetic route of these structures, which are composed of spherical silica spheres surrounded by a varying number of polystyrene nodules, consists in the emulsion polymerization of styrene in presence of silica particles, which have been surface-modified by a coupling agent containing polymerizable groups.

We have demonstrated that the colloidal clusters' morphologies result from the minimization of an energy term, which is the sum of an attraction towards the centre and two-body particle repulsions which can balance the attractive central force. By varying the size of silica seeds, the number of latex particles growing on their surface could be controlled and predicted morphologies were observed, including line segments, triangles, tetrahedra, etc. A main advantage of this technique is also that we can precisely control the reaction time, allowing us to tune the final morphology of the colloidal clusters.