Synthesis of a Colloidal Molecule from Soft Microgel Spheres

Colloidal clusters, or colloidal molecules, are more powerful model systems and building blocks than colloidal spheres; however, their synthesis still remains a huge challenge. In addition, only colloidal molecules composed of hard spheres were synthesized up to now. Here we report the synthesis of a colloidal cluster from soft poly(N-isopropylacrylamide) (PNIPAM) microgel spheres. The microgel spheres were first assembled into highly ordered colloidal crystals. Spheres with surface vinyl groups were then covalently bonded with the surrounding spheres with surface thiol groups via in situ thiol-ene reaction. The resulting clusters consist of 13 microgel spheres with 1 vinyl-modified sphere in the center and 12 thiol-modified ones coordinated around. Their size can be tuned by changing temperature. A preliminary test suggests that they can act as nuclei for microgel spheres to aggregate into dendritic structures.