Department of Chemistry , University of Utah , Salt Lake City , Utah 84112 , United States.
J Am Chem Soc. 2019 Feb 6;141(5):1980-1988. doi: 10.1021/jacs.8b10752. Epub 2019 Jan 25.
Self-assembly of nanocrystals into functional materials requires precise control over nanoparticle interactions in solution that are dominated by organic ligands that densely cover the surface of nanocrystals. Recent experiments have demonstrated that small truncated-octahedral nanocrystals can self-assemble into a range of superstructures with different translational and orientational order of nanocrystals. The origin of this structural diversity remains unclear. Here, we use molecular dynamics computer simulations to study the self-assembly of these nanocrystals over a broad range of ligand lengths and solvent conditions. Our model, which is based on a coarse-grained description of ligands and solvent effects, reproduces the experimentally observed superstructures, including recently observed superlattices with partial and short-ranged orientational alignment of nanocrystals. We show that small differences in nanoparticle shape, ligand length and coverage, and solvent conditions can lead to markedly different self-assembled superstructures due to subtle changes in the free energetics of ligand interactions. Our results rationalize the large variety of different reported superlattices self-assembled from seemingly similar particles and can serve as a guide for the targeted self-assembly of nanocrystal superstructures.
纳米晶体制成功能材料需要精确控制纳米颗粒在溶液中的相互作用，这些相互作用主要由密集覆盖在纳米晶表面的有机配体主导。最近的实验表明，小的截断八面体纳米晶可以自组装成具有不同纳米晶平移和取向有序的一系列超结构。这种结构多样性的起源尚不清楚。在这里，我们使用分子动力学计算机模拟来研究在广泛的配体长度和溶剂条件下这些纳米晶的自组装。我们的模型基于对配体和溶剂效应的粗粒化描述，再现了实验观察到的超结构，包括最近观察到的具有纳米晶部分和短程取向排列的超晶格。我们表明，由于配体相互作用自由能的细微变化，纳米颗粒形状、配体长度和覆盖率以及溶剂条件的微小差异会导致明显不同的自组装超结构。我们的结果合理化了从看似相似的颗粒中自组装的大量不同的报道超晶格，并可以作为纳米晶体超结构有针对性自组装的指南。
