Molecular Dynamics Simulation Study on Self-Assembly of Polymer-Grafted Nanocrystals: From Isotropic Cores to Anisotropic Cores.

Abstract

The self-assembly of polymer-grafted nanocrystals (PGNCs) is an important method to manufacture novel nanomaterials. Herein, we focus on the self-assembly of three types of PGNCs with differently shaped cores including sphere, octahedron, and cube by molecular dynamics simulation. By characterizing the positional and orientational order of the assembled superlattices, we construct the phase diagrams as a function of the grafting density and polymer chain length. For PGNCs with spherical cores, we observe the transition from the FCC phase to the BCC phase due to the packing entropy of the ligand polymer chains. For PGNCs with anisotropic cores, the close-packed FCC phase is replaced by the C-BCC phase (octahedral cores) or the C-triclinic phase (cubic cores) due to the directional entropy of core shape. We also study the assembly dynamics by tracking the time evolution of the positional and orientational order. We elucidate the relationship of grafting density and polymer chain length to the packing entropy and directional entropy and reveal their important effects on assembled structures. In general, our simulation results provide useful guidelines for the programmable assembly of PGNCs.