Coassembly of Janus Nanoparticles in Asymmetric Diblock Copolymer Scaffolds: Unconventional Entropy Effect and Role of Interfacial Topology

The coassembly of Janus nanoparticles and block copolymers offers a unique approach to control the spatial organization of nanoparticles. Herein, using computer simulations and theoretical analysis, we explore the hierarchical structures and underlying mechanisms of the coassembly of symmetric Janus nanoparticles in asymmetric block copolymers. Our simulations constitute the first study clarifying that Janus nanoparticles with two symmetric surface moieties do not take symmetric distribution in the interfaces of asymmetric block copolymers. Rather, they take various but controllable off-center arrangements from the interfaces upon tailoring the molecular architectures of block copolymers and thereby controlling their resulted mesostructural topology. We examine the detailed mechanism of this mesostructural topology-mediated hierarchical assembly and find that the structural asymmetry of the block segments causes unconventional entropy effect at the molecular scale, and the curved interfaces can lead to topology mismatching between Janus nanoparticles and polymer interfaces at the mesoscale. Furthermore, we employ a micromechanical model to demonstrate that the deviation of the Janus nanoparticles from the interface can significantly influence the mechanical properties of the nanocomposites. These findings enrich our understanding on the thermodynamic nature of polymer nanocomposites and may suggest a novel design approach to precisely program the spatial organization of nanoparticles in polymer matrix.