Direct Observation of Nanoparticle Self-Assembly Dynamics at the Water−Air Interface Using Differential Interference Contrast Microscopy

Understanding the dynamics of the nanoparticle (NP) self-assembly process is very important for both fundamental and applied research of functional nanomaterials. In this report, high-contrast differential interference contrast microscopy was used for real time observation of evaporation-mediated self-assembly of gold nanoparticles (GNPs) at the water−air (w/a) interface. GNPs were found to be trapped at the w/a interface and gradually assembled into clusters. The dynamic cluster formation process was driven by evaporation-induced electrostatic repulsion decrease and can be divided into two stages. During the whole period, individual particles moved in random patterns that were indistinguishable from those produced by computer simulation of two-dimensional random walk, but interactions with surrounding particles and clusters caused a more directional flow motion. The observed dynamics of GNP cluster formation is more like the reaction-limited cluster formation model where the sticking probability is less ...