Chemical characterization of fluorinated/hydrogenated mixed monolayers grafted on gold nanoparticles

Abstract

Perfluorocarbons are omniphobic compounds as a consequence of their unique properties such as, e.g., high electronegativity, low polarizability, high ionization energy, and low surface tension. The possibility of combining such properties with the features of nanoscale materials promoted a recent upsurge in the production of fluorinated nanoparticles for application in different fields. Attainment of mixed fluorinated/hydrogenated stabilizing layers is also desired in some cases, but often the composition of the ligand mixture used in the exchange reaction is not reflected in the resulting monolayer. Thus, methodologies for determining the resulting chemical composition of the final mixed fluorinated/hydrogenated monolayers grafted on the nanoparticle (NP) surface are needed. Here we propose a combined Fourier Transform Infrared (FTIR) and X-ray Photoemission Spectroscopy (XPS) investigation for assessing the final chemical composition of a mixed monolayer of hydrogenated and fluorinated alkanethiols grafted on the surface of gold NPs obtained through two different synthetic routes. This analysis allowed the evaluation of the exchange efficiency of the two synthetic routes, and also, coupled with UV–vis studies, highlighted that the colloidal stability of the final NPs was not only dependent on the fluorinated/hydrogenated ratio but also on the chosen exchange route, which seems to influence the ligand organization on the mixed monolayer.