Superstructural phase transitions in polymer-grafted nanooctahedra

Currently, there exists a large space of experimental parameters that can be employed to direct nanoscale assemblies. Tuning such experimental handles produces different modes of inter-particle associations such as hard particle packing, soft inter-penetrable ligand shells, or patchy/selective attraction. In particular, polymer ligands are of interest as they enable tunable nanocrystal softness through modifications of polymer molecular weight and grafting density. Here, we investigate phase transitions in polymer-grafted nanooctahedra by varying polymer length, nanocrystal size, truncation, and ligand density. In two-dimensional superlattices, longer polymers or smaller nanooctahedra induce a transition from orientationally ordered to hexagonal rotator lattices. In three-dimensional superlattices, increasing polymer length drives transitions from Minkowski to body-centered cubic and plastic hexagonal close-packed phases, while higher grafting densities further enable transitions to simple hexagonal phases. Our integrated experiment, simulation, and theory work highlights the versatility of polymer-grafted anisotropic nanocrystals as building blocks for designing hierarchical superstructures and metamaterials with customizable properties.