Assembly of Nanoparticles into “Colloidal Molecules” : Toward Complex and yet Defined Colloids with Exiting Perspectives

Abstract

In line with atoms being the elementary units of molecules and crystals, colloidal particles can be used as building blocks for organized materials. A major benefit in doing so is that joining colloids in a defined manner comes along with structuring. In view of opening avenues to more complex structural motifs, significant efforts must be geared to colloids with specific shapes and symmetries. A straightforward strategy is joining equal‐sized spherical particles into stable clusters. Such clusters are called “colloidal molecules” because they may exhibit configurations resembling pretty much those of molecules. Their preparation can be based on the agglomeration of particles dispersed in an emulsion. The particles adsorb on the emulsion droplets and coagulate in a defined way during the evaporation of the droplet phase. Using this method originally applied to microscale particles, one can produce clusters with submicronsized global dimensions. Variable parameters such as radii and concentration of cluster constituents provide the framework needed to obtain “colloidal molecules” that differ in size, shape, and physical properties. This opens up exciting perspectives for tailormade colloids as building units for hierarchically organized materials. Moreover, new physical properties such as plasmonic “hotspots” may emerge from packing particles into assemblies of specific configurations.