Controlling the radial position of nanoparticles in amphiphilic block-copolymer assemblies

Unique radial arrays of quantum dots can be formed by the cooperative self-assembly of quantum dots and amphiphilic block-copolymers. Here, we report the effect of nanoparticle volume fractions as well as the length and concentration of polymers on the self-assembly structure. It was found that the size of the assemblies and the radial position of nanoparticles can be effectively controlled by changing the volume fraction of nanoparticles. Contrary to the typical trend observed for homogeneous incorporation of nanoparticles, increases in nanoparticle volume fractions resulted in decreases in the size and size distribution of the assemblies over a wide nanoparticle volume fraction range. The strong segregation theory calculations indicate that the structural change is due to a balance between the chain stretching energy and the interfacial energy between the two blocks. In addition, the coassemblies became larger with increasing nanoparticle sizes at maximum nanoparticle volume fractions. However, the polymer length did not significantly affect the structural parameters at maximum nanoparticle volume fractions. These findings indicate that the design rules established for the self-assembly of amphiphilic block-copolymers do not directly apply to the coassembly structure with nanoparticles and that the nanoparticles play an active role in the self-assembly.