Lee Won Chul, Kim Byung Hyo, Choi Sun, Takeuchi Shoji, Park Jungwon
Department of Mechanical Engineering, Hanyang University , Ansan, Gyeonggi 15588, Republic of Korea.
Institute of Industrial Science, The University of Tokyo , Tokyo 153-8505, Japan.
J Phys Chem Lett. 2017 Feb 2;8(3):647-654. doi: 10.1021/acs.jpclett.6b02859. Epub 2017 Jan 23.
Drying a colloidal solution of nanoparticles is a versatile method to construct self-assembled structures of nanoparticles. However, mechanistic understanding has mostly relied on empirical knowledge obtained from the final structures of self-assembly as relevant processes during solvent drying are likely kinetic and far from equilibrium. Here, we present in situ TEM studies of nanoparticle self-assembly under various conditions, including the concentrations of the initial solution and the types of nanoparticles and substrates. The capability of tracking trajectories of individual nanoparticles enables us to understand the mechanisms of drying-mediated self-assembly at the single-nanoparticle level. Our results consistently show that a solvent boundary primarily affects nanoparticle motions and the resulting self-assembly processes regardless of different conditions. The solvent boundary drives nanoparticles to form two-dimensional assembly mainly through two pathways, transporting scattered nanoparticles by lateral dragging and flattening aggregated nanoparticles by vertical pressing.
干燥纳米颗粒的胶体溶液是构建纳米颗粒自组装结构的一种通用方法。然而，机理理解大多依赖于从自组装最终结构获得的经验知识，因为溶剂干燥过程中的相关过程可能是动力学的且远离平衡态。在这里，我们展示了在各种条件下纳米颗粒自组装的原位透射电子显微镜研究，包括初始溶液的浓度、纳米颗粒的类型和基底。追踪单个纳米颗粒轨迹的能力使我们能够在单纳米颗粒水平上理解干燥介导的自组装机制。我们的结果一致表明，无论条件如何，溶剂边界主要影响纳米颗粒的运动以及由此产生的自组装过程。溶剂边界主要通过两种途径驱动纳米颗粒形成二维组装，即通过横向拖动运输分散的纳米颗粒以及通过垂直挤压使聚集的纳米颗粒变平。
