Understanding the mechanisms of crystallization and reconfiguration of anisotropic nanoparticle superlattices

Crystallization is a universal phenomenon. Yet, despite its importance in wide-ranging technologies and natural processes, there is no single theoretical framework that accurately describes diverse crystallization phenomena. Recent breakthroughs in liquid cell transmission electron microscopy (LCTEM) have enabled direct, in situ visualization of nanoparticle systems, including their self-organization into and between distinct superlattices. In this work, we elucidate the complex, solvent-dependent phase behavior and crystallization pathways of polymer-grafted gold nanocubes into ordered superlattices. To explain observations from LCTEM experiments, we develop a computational model that reproduces the experimental phase behavior and show that variable charge screening by the solvent drives the assembly of the nanocubes into different phases. We show that the self-assembly of the different phases follows distinct kinetic pathways; in particular, the assembly of the rhombic phase proceeds via a decoupling of translational and orientational order. Moreover, experiments and simulation reveal a reversible transition between the square-like and rhombic phases and find a hexagonal rotator-like intermediate phase along the transition pathway. These findings open the door for understanding—and hence manipulating—complex microscopic crystallization pathways and phase transition kinetics of anisotropic nanoparticles.