Self-Assembly of Binary Nanocrystals Grafted with End-Functionalized Polymers: A Molecular Dynamics Simulation Study

Self-assembly of polymer-grafted nanocrystals (PGNCs) has become an area of increasing interest, as the polymer ligands can have rich conformations and be functionalized with diverse end groups and the interplay of conformational entropy and distinctive interaction enthalpy facilitates the programmable self-assembly of nanocrystals into ordered superlattice structures with superior properties and novel applications. This is especially true for the binary end-functionalized PGNCs, the numerous design parameters offer many new opportunities to create abundant and sophisticated binary nanocrystal superlattices (BNSLs). However, our understanding of assembled structures, assembly mechanisms and design parameters' effects is fairly limited. For the most-studied end-functionalized PGNC, Nanocomposite tecton (NCT), only two types of BNSLs were observed, revealing a significant gap between its rich parameter space and the actual selectivity of assembled structures. In this work, we focus on the generic self-assembly behavior of binary end-functionalized PGNCs using molecular dynamics simulations. By systematically tuning the key design parameters, we achieve the self-assembly of a series of BNSLs including the experimentally observed CsCl (BCC) and Th₃P₄ as well as AlB₂, Cr₃Si, and Cs₆C₆₀. By examining the relative stabilities of different phases in the overlapping regions of the separate phase diagrams for different stoichiometries, we construct the phase diagram for the most stable phase in different binary combinations of end-functionalized PGNC systems. Our BNSLs display multivalent cluster properties analogous to NCTs. By investigating the assembly dynamics, we find that due to the attraction interactions between end groups, multivalent hybridization occurs, leading to the formation of clusters and various BNSL.