The van der Waals Interactions of n‐Alkanethiol‐Covered Surfaces: From Planar to Curved Surfaces

Abstract

The van der Waals (vdW) interactions of n‐alkanethiols (ATs) adsorbed on planar Au(111) and Au(100) surfaces and curved Au nanoparticles of different diameters are reported. By means of electrochemical measurements and molecular dynamic calculations, the increase in the average geometrical curvature of the surface influences the global interactions, that is, decreasing vdW interactions between neighboring molecules. Small NPs do not present the same electrochemical behavior as planar surfaces. The transition between nanoparticle to flat surface electrochemical response is estimated to occur at a circa 13–20 nm diameter range.

Solvent-Ligand Interactions in Colloidal Nanocrystals

“…These observations are entirely consistent with our model. In general, the curvature of the nanocrystal surface decreases at larger sizes and the ligands are forced closer to each other, 41 excluding solvent and increasing heterogeneity. However, for large nanocrystals, the curvature is already small and further increasing the nanocrystal size does not decrease the curvature significantly.…”

Solvent‐Limited Ion‐Coupled Electron Transfer and Monolayer Thiol Stability in Au144 Cluster Films

“…Moreover, the stability of thiol SAMs on Au surface can be evaluated by the well-known electrochemical reductive desorption method. [18] The position of the desorption peak potential in the reductive desorption process can be considered as a measure of SAMs stability. The reductive desorption data for the PET protected curved Au 144 showed two peaks at À 1.18 V and À 1.26 V vs. Ag/AgCl (Figure 3g).…”

“…The relative difference of the desorption potential in the two system is~0.1 V. This data is in agreement with recent studies of electrochemical reductive desorption of alkanethiols on bulk Au and NP surfaces. [18] I.e., a higher reduction potential is required to desorb the thiols from the NPs (curved) surface compared to the bulk Au (flat) surface. The stability of thiol-based SAMs on the noble metal surfaces was dictated by various parameters, for example, intermolecular interactions, [19] AuÀ SÀ C bond angle (even-odd effect), [20] binding strength of AuÀ S on different facets [21] and the surrounding medium.…”

“…Usually, the packing density of SAMs on the NP surface is lower than on the planar Au surface resulting in lower Van der Waals interactions between the molecules on the NP surface. [18,23] However, although, the packing density of alkanethiols on NPs is lower, they still exhibit greater chemical stability than thiols on a planar Au surface. [18] Similarly, the photothermal (light to heat) conversion efficiency is higher for Au nanoclusters and they hold the peripheral PET monolayers more strongly compared to the bulk Au surface, [24] as shown in figure 3e and 3f.…”

“…[25] The tangential mode corresponds to the shorter AuÀ S bonds involved in the staple motif (Au(staple)-S(staple) bonds). These type of staple motif structures on the Au clusters are very well known, as evidenced by the X-ray structure of the crystallized cluster compounds such as Au 25 (PET) 18 , Au 38 (PET) 24 and many others. [26] While on the polycrystalline bulk Au surface (Figure 4b) two peaks centered at 293 and 322 cm À 1 with the different relative intensities were also observed.…”