Vibrational Spectroscopic Studies on the Formation Processes and Characteristics of Octadecanethiol Monolayers on the Surfaces of Gold Nanoparticles

Abstract

The preparation method of hydrophobic gold nanoparticles (AuNPs) with the diameters of 17, 30 and 48 nm has been developed. So as to clarify the size effects of AuNPs on the hydrophobization processes, time courses for the formation of the self-assembled monolayers (SAMs) of octadecanethiol (ODT) molecules on the surfaces of the AuNPs have been investigated by means of FT-IR and Raman spectroscopies. In all cases, the alkyl chains were mainly arranged as all-trans conformation (solid-like) at the completion of the reaction. Observation of the time course of ODT-SAM formation revealed that smaller curvature (larger size) resulted in the faster formation of SAM because of smaller conical volume snugly available for the alkyl chain on the surface of the AuNP.