(510i) Conformational Entropy Mediated Orientation of Ligated Nanocrystals

In self-assembled structures, the orientation of hard-core, polyhedral nanocrystals (NCs) is dictated by packing entropy, but when these NCs are coated in a soft ligand layer, their rotational ordering becomes unpredictable due to competing interactions of the core and organic ligands. To address this gap, we investigated the role of the conformational entropy of the ligand layer in determining the orientation of polyhedral NCs in self-assembled structures.

With a framework combining numerically derived ligand density distributions and analytical expressions for the freely jointed chain model, we predict NC orientation for a variety of polyhedral shapes, self-assembled structures, and ligand lengths. Additionally, we compare to rotationally disordered NCs to estimate the driving force for nanocrystal orientation, finding a strong dependence on both NC shape and ligand length. We test the predictive ability of this framework by comparing to the experimentally observed orientation of cuboctahedral PbS NCs in BCC and FCC superlattices. Our work offers a tractable starting point for the thermodynamic understanding of polyhedral NCs with competing core-ligand interactions and may inform experimental efforts to achieve the self-assembly of coherently oriented NCs.