Dictating Orientation Diversity of Body-Centered Cubic Superlattices in the Self-Assembly of Polymer-Grafted Nanocubes through Heterogeneous Grafting Designs

Abstract

Understanding the self-assembly of polymer-grafted nanocrystals with anisotropic cores and precisely controlling the orientation of their assembled structures are crucial for creating novel nanomaterials with remarkable photoelectric, optical, and catalytic properties. Herein, we design three types of polymer-grafted nanocubes that exhibit spatially heterogeneous grafting with region-specific differences in grafted chain length and investigate their self-assembly using molecular dynamics simulation. By determining the effective shapes of the nanocrystals and quantifying their sphericity, we find that the grafting conditions (i.e., grafting patterns and grafting chain lengths) significantly influence their shape anisotropy. Furthermore, we construct the phase diagrams as functions of the face-centered grafting chain length and the non-face-centered grafting chain length for the three grafting patterns. Under different grafting conditions, six types of BCC superlattices with distinct orientational order are observed, including C-BCC, dC-BCC, E-BCC, T-BCC, A-BCC, and I-BCC, where the C-BCC superlattices have not yet been obtained through kinetic self-assembly of polymer-grafted nanocubes in past simulations. We find that the orientational order of the assembled superlattices is governed by the combined effects of the directional entropy forces of the nanocrystals and the packing entropy of the grafted polymer chains. In general, our simulation results provide valuable guidelines for creating novel superstructures and tuning the orientational order of superlattices in the self-assembly of polymer-grafted nanocubes.