The impact of surface chemistry on the interfacial evaporation-driven self-assembly of thermoplasmonic gold nanoparticles

This paper reports an interfacial evaporation-driven approach for self-assembly of a gold nanoparticle (AuNP) film at the interface of liquid/air. We have designed colloidal plasmonic AuNPs capped with different types and surface coverage densities of ligands (i.e. purified and unpurified oleylamine-capped or thiol-protected AuNPs) and studied the impact of surface chemistry on the self-assembly of AuNPs using the optically excited plasmonic heating effect. By employing the extended DerjaguinLandau–Verwey–Overbeek model, the calculated lowest potential energies of the assembled AuNPs capped with purified oleylamine or alkyl thiols are between −1 kBT and −2 kBT, which is close to the room temperature thermal energy and represents a meta-stable assembly, indicating the reversible self-assembly of the AuNP film observed from the experiment. Furthermore, we observed the superheating phenomenon in well-dispersed nanoparticle solution while normal boiling occurred in the solutions with AuNP assemblies. The SERS activity of the as-prepared AuNP film has also been studied using rhodamine 6G as a molecular probe. This work not only provides a new aspect of the boiling phenomena of optically heated colloidal plasmonic nanoparticle solutions, but also provides inspiration for a new approach in designing surface ligands on the nanoparticles to realize reversible self-assembly via interfacial evaporation.