Controlling 2D Nanoparticle Self-Assembly Mesophases via Symmetry Breaking Driven by Single Bottlebrush Polymer Conjugation

Polymer grafting density critically influences the self-assembly of polymer-grafted nanoparticles, yet the low grafting density regime remains underexplored. Here, we investigate the thin-film self-assembly of bottlebrush polymer-grafted core/shell nanoparticles (BPGNPs) under quasi-2D confinement at near-zero grafting densities through coarse-grained molecular dynamics (CGMD). The NP core is modeled using a hard-core/soft-shoulder (HCSS) potential, and it is compared against Weeks-Chandler-Andersen (WCA) potential. While the phase behaviors of both models are well-known, the distinct phase behaviors of both models persist even with polymer grafting offering additional room for tunability. Unlike sufficiently high grafting density or bare nanoparticles (NPs), grafting a single bottlebrush polymer breaks the rotational symmetry. The resulting structural polarity of grafted NPs can be precisely controlled through bottlebrush design parameters. We demonstrate that enhanced structural polarity stabilizes specific ordered phases, enabling precise control over self-assembled morphologies such as hexagonal lattices, square lattices, and linear clusters. Lastly, we explore the impact of synthesis-induced heterogeneity by introducing bare NPs, dual-polymer-grafted particles, and unconjugated polymers as minor species, providing insights into morphological stability under realistic grafting conditions. This work advances our understanding of BPGNP self-assembly in the near-zero grafting density regime and establishes design principles for functional nanotechnology applications.