Native Ligand Shell Rigidity and Crosslinking Ligand Dimensions Determine Interparticle Spacing In 2-D Arrays of Covalently-Crosslinked Gold Nanoparticle Films

Abstract

Alkane thiol-capped gold nanoparticles were compressed into 2-d arrays using a Langmuir trough, and covalently crosslinked using a solution of alkanethiols to yield a flexible film of nanoparticles. These nanoparticles were prepared via Brust route and differed only in the length (L) of the alkyl chain of the thiol. Nanoparticle 2-d arrays were transferred to a substrate by Langmuir-Blodgett deposition and imaged using Transmission Electron Microscopy to analyze interparticle spacing. It was found that for films of nanoparticles with softer, liquid like native ligand shells, the interparticle spacing with the finished array was dictated by the length of the incoming crosslinking agent. Conversely, nanoparticles with rigid, semi-crystalline native ligand shells maintained predictable interparticle spacing of 2L, in accord with the thickness of the ligand shell. Crosslinking attempts with 1,6-hexanedithiol determined that the molecule was too short to effectively function as a crosslinker. In contrast 1,6-hexane bis(11- mercaptoundecanoate) was found to be too long to effectively function as a crosslinker. Computational analysis using Gaussian View and the Blugold Supercomputing Cluster showed that 1,6-hexane bis(11-mercaptoundecanoate) maintains a cyclic structure in chloroform solution, inhibiting its capacity to perform the crosslinking reaction.