Assembling nanoparticles into organized structures gives rise to collective properties that emerge from electronic and optical coupling, which opens up new opportunities for various nanotechnological applications. Block copolymers (polymers consisting of sequences of different repeat units), which phase separate into periodic nanostructures of controlled size and morphology, bear the greatest potential for organizing nanoparticles over square centimeter areas in a single step. In this work we focused on nanoparticles that are designed to segregate selectively to one type of block copolymer domains but retain a high packing tendency. The results reveal the mutual influence between the natural morphology of the block copolymer and the nanoparticle shape-dependent packing tendency on the resulting structure. Insights gained from this study further enhance our ability to obtain hierarchically ordered nanocomposites and to control their structures in thin films.
Macromolecules 2014, 47, 3022-3032.
Amit Halevi,1 Shira Halivni,1 Meirav Oded,1 Axel H. E. Müller,2 Uri Banin,1 , Roy Shenhar1,*
1-Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel and
2-Institute of Organic Chemistry, University of Mainz, 55099 Mainz, Germany.
The co-assembly of A-B diblock copolymers with B’-type nanoparticles (i.e., nanoparticles that are slightly incompatible with the B domain) leads to hierarchical structures, where the block copolymer phase separates first and the nanoparticles create close-packed arrays within the B domains due to a slower, secondary phase separation process. Here we report the results of a comprehensive study, which focused on two aspects: the influence of the nanoparticle shape (spherical vs. rod-like) and the effect of the volume composition of the blocks. Three polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers featuring similar molecular weights but differing in PS volume fraction were mixed with spherical and rod-shaped poly(ethylene oxide) (PEO)-capped CdS nanoparticles at different filling fractions and cast as thin films. Our results highlight the mutual influence between the block copolymer and the nanoparticles on the resulting morphology, demonstrating the ability to control the film morphology by the filling fraction of the nanoparticles and their tendency to localize at the film surface, and by confinement-induced nanoparticle aggregation. Most importantly, the results reveal the influence of the nanoparticle shape on the structure of the film.