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 gold nanoparticles (AuNPs) 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 by using the optically excited plasmonic heating effect. By employing the Extended Derjaguin Landau Verwey Overbeek model, the calculated lowest potential energies of assembled AuNPs capped with purified oleylamine or alkyl thiols are between -1 k_B T and -2 k_B T, which is close the room temperature thermal energy and represents meta-stable assembly, indicating the reversible self-assembly of AuNPs film observed from experiment. Furthermore, we observed superheating phenomenon in well-dispersed nanoparticles solution while normal boiling occurred in the solutions with AuNPs assemblies. The SERS activity of as-prepared AuNPs film has also been studied by using Rhodamine 6G as a molecular probe. This work not only provides a new aspect of boiling phenomena of optically heated colloidal plasmonic nanoparticle solutions, but also offers inspiration for new approach in designing surface ligands on the nanoparticles to realize reversible self-assembly via interfacial evaporation.