From Evaporation to Self-Assembly: Deposition Kinetics and Mechanisms of Nanoparticles in Colloidal Droplets.

Abstract

The self-assembly of nanoparticles (NPs) represents a key strategy for fabricating 2D functional nanostructures. However, achieving precise control over deposition kinetics remains challenging due to the complex multiphase interactions within the Substrate-Droplet-NP system, limiting the self-assembly quality. Here, we investigated the deposition behavior of NPs on heated substrates using molecular dynamics simulation techniques. By analyzing the interactions of Droplet-NP and Substrate-NP, the intrinsic mechanism of self-assembly was revealed. Results demonstrate that strong Substrate-NP van der Waals (S-N vdW) interactions result in high adsorption energy, thereby enhancing the thermal stability of the deposited NPs. Moreover, the interaction of Droplet-NP plays a crucial role in determining the assembly morphology. Strongly hydrophobic NPs accumulate at the gas-liquid interface and migrate toward the three-phase contact line (TPCL) under the combined influence of the S-N vdW interactions and the NPs concentration gradient-driven diffusion. For NPs with small diameters (0-2 nm), the deposition rate at the TPCL exceeds the retraction rate of the TPCL, ultimately forming a ring-like structure. However, for NPs with larger diameters (>3 nm), a faster droplet retraction than the deposition rate at the TPCL drives the NPs to self-assembly into a film-like structure. In contrast, hydrophilic NPs remain dispersed within the droplet uniformly and transported toward the liquid-solid interface, forming a dense film-like structure on the substrate. These findings provide guidance for the precise creation of nano-self-assembled structures.