Nanoparticles (NPs) comprised of noble metal cores and organic ligands have been widely used in many engineering applications in the recent years due to their exceptional material properties. Numerous studies have explored the tunability of the elastic and electronic transport properties of nano-scale thin films made of gold nanoparticles. However, the nanoscale mechanisms, such as the conformation of ligands, cross-linking behavior, are still not well understood. In this study, we developed a full atomistic modeling approach to construct full atomistic cross-linked gold nanoparticle thin films to explore the nanoscale features and molecular configurations of cross-linked gold nanoparticle assemblies at the nano-scale.

Nanoparticle assemblies have incredible flexibility and tunable electrical and mechanical properties. Thin films containing gold nanoparticles (GNPs) are among the best candidates for various applications, such as touch sensors, strain gauges, and vapor sensors. Recently, covalently cross-linked GNP thin films with enhanced electrical properties and mechanical stability were fabricated by layerby-layer spin-coating. Researchers found experimentally that the elastic modulus of such films can be tuned in the range of 3.6−10 GPa by controlling the core size, degree of order, ligand length, and so forth. However, few molecular studies have illuminated the molecular mechanisms of cross-linked NP thin films. Here, we demonstrated direct atomistic modeling of alkanedithiol cross-linked GNP thin films and probed the mechanical properties by tensile test simulations. We showed that the Young's modulus values obtained from our models are consistent with the experimental results. We also revealed that the mechanical properties of thin films depended on the ligand length, core size, and grafting density. Our results showed that the number of all-trans bridge linkers dominates the Young's modulus of the thin films. This study provides molecular insights into the role of cross-linkers in the mechanical responses of GNP assemblies and provides fundamental information for the design of thin films, which could benefit many applications.