(127g) Crystal-Phase Polymorphism in Nanoplates Via Competition between Energy and Entropy

The ability to synthesize anisotropic particles on the colloidal and nanoscale has resulted in an explosion in the number of self-assembled superlattices in recent years. Still, the complex interactions between particles inhibits a priori structure prediction, making it difficult to design systems that self-assemble into prescribed structures. One angle from which to examine this problem is to take a top-down approach and consider particle shape (entropic) and patchy(energetic) interactions separately. Here, we computationally study the self-assembly and phase behavior of a model system where the competition between energetic and entropic effects can be tuned from antagonistic to synergistic. The model is a two-dimensional patchy triangular nanoplate, where the locations of the patches on the particles allow the particle shape and patchy interactions to favor either the same or different local motifs. In the antagonistic case, the competition between the energetically favored motifs and entropically favored packing results in a rich phase diagram with a crystal-phase polymorphism that is not observed in the synergistic case. We report the self-assembly of two new crystal structures. These results illustrate how the interplay between energetic and entropic effects can affect the phase diagram of a system, which can be useful for designing reconfigurable materials.