The Role of Cross-Linkers in the Mechanical Responses of Gold Nanoparticle Assemblies

Nanoparticle assemblies have incredibleflexibility andtunable electrical and mechanical properties. Thinfilms containing goldnanoparticles (GNPs) are among the best candidates for variousapplications, such as touch sensors, strain gauges, and vapor sensors.Recently, covalently cross-linked GNP thinfilms with enhancedelectrical properties and mechanical stability were fabricated by layer-by-layer spin-coating. Researchers found experimentally that the elasticmodulus of suchfilms can be tuned in the range of 3.6-10 GPa bycontrolling the core size, degree of order, ligand length, and so forth.However, few molecular studies have illuminated the molecularmechanisms of cross-linked NP thinfilms. Here, we demonstrateddirect atomistic modeling of alkanedithiol cross-linked GNP thinfilms and probed the mechanical properties by tensile testsimulations. We showed that the Young's modulus values obtained from our models are consistent with the experimental results. Wealso revealed that the mechanical properties of thinfilms depended on the ligand length, core size, and grafting density. Our resultsshowed that the number of all-trans bridge linkers dominates the Young's modulus of the thinfilms. This study provides molecularinsights into the role of cross-linkers in the mechanical responses of GNP assemblies and provides fundamental information for thedesign of thinfilms, which could benefit many applications.