Effect of geometric constraints on the self-assembled monolayer formation of aromatic disulfides on polycrystalline gold

The self-assembled monolayer (SAM) formation tendency of two comparatively small aromatic disulfide molecules, namely naphthalene disulfide (NDS) and diphenyl disulfide (DDS), has been investigated using quartz crystal microgravimetry (QCM), cyclic voltammetric, and impedance techniques. The typical time period for monolayer formation on polycrystalline gold has been found to be about 2 h for both the molecules from the QCM data. A significant change in double-layer capacitance values (from 21 μF/cm2 for bare gold to ∼14 and ∼8 μF/cm2 for NDS and DDS, respectively) upon monolayer formation for both the cases has been observed, which correlates well with the QCM area per molecule values (∼49 and 36 A2 for NDS and DDS, respectively). The difference in the permeability of the two monolayers to simple ionic species was also investigated using K3Fe(CN)6 as redox probes in aqueous solution. A mixed linear/radial mode of diffusion is observed at the DDS-modified electrode in contrast to a predominant linear one ...