Physical and Computational Sciences Directorate , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.
Nano Lett. 2018 Oct 10;18(10):6551-6556. doi: 10.1021/acs.nanolett.8b03139. Epub 2018 Sep 7.
During nanoparticle coalescence in aqueous solution, dehydration and initial contact of particles are critically important but poorly understood processes. In this work, we used in situ liquid-cell transmission electron microscopy to directly visualize the coalescence process of Au nanocrystals. It is found that the Au atomic nanobridge forms between adjacent nanocrystals that are separated by a ∼0.5 nm hydration layer. The nanobridge structure first induces initial contact of Au nanocrystals over their hydration layers and then surface diffusion and grain boundary migration to rearrange into a single nanocrystal. Classical density functional theory calculations and ab initio molecular dynamics simulations suggest that the formation of the nanobridge can be attributed to the accumulation of auric ions and a higher local supersaturation in the gap, which can promote dehydration, contact, and fusion of Au nanocrystals. The discovery of this multistep process advances our understanding of the nanoparticle coalescence mechanism in aqueous solutions.
在纳米颗粒在水溶液中的聚并过程中，颗粒的去水合和初始接触是非常重要但却知之甚少的过程。在这项工作中，我们使用原位液/ 池透射电子显微镜直接观察到了 Au 纳米晶体的聚并过程。研究发现，在由约 0.5nm 水化层隔开的相邻纳米晶体之间形成了 Au 原子纳米桥。该纳米桥结构首先诱导 Au 纳米晶体在其水化层上发生初始接触，然后通过表面扩散和晶界迁移重新排列成单个纳米晶体。经典密度泛函理论计算和从头算分子动力学模拟表明，纳米桥的形成可归因于金离子的积累和间隙中更高的局部过饱和度，这可以促进 Au 纳米晶体的去水合、接触和融合。这一多步过程的发现增进了我们对水溶液中纳米颗粒聚并机制的理解。
