Importance of Polymer Ligand Conformation to Entropy-Driven Assembly of Nanoparticles within Block Copolymer Particles

The conformation of polymer brushes can direct the nanostructures of hybrid materials as it affects the entropic interactions between grafted chains and matrix chains. Herein, we demonstrated the precise spatial alignment of polystyrene-grafted Au nanoparticles (Au@PS) within onion-like polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) particles depending on the parameters related to the conformation of PS ligands, including the ratio of PS block molecular weight (M_n) to PS ligand M_n (P/N), core size of Au@PS (r), and grafting density of PS ligands (σ). Change in any of the parameters drives dramatic morphological transitions of hybrid particles. PS ligands having low interfacial interactions with BCP chains were excluded from the BCP domains. In contrast, high interfacial interactions between Au@PS and BCP chains allowed the formation of Au@PS arrays within PS blocks. To evaluate the entropic interactions, a modified swelling ratio (P/N_SDPB) is proposed by considering the ligands in the semi-dilute polymer brush (SDPB) regime as the only brushes available for interfacial interactions with BCPs. In addition, the effect of nanoparticle size was taken into account for a comprehensive understanding of the entropic interactions in the hybrid system.