  Molecular adhesion promoters are a central component of modern coating
systems for the corrosion protection of structural materials. They are
interface active and form ultrathin corrosion inhibiting and adhesion-promoting
layers. Here we utilize thiol-based self-assembled monolayers (SAMs) as model
system for demonstrating a comprehensive combinatorial approach to understand
molecular level corrosion protection mechanisms under anodic polarization.
Specifically, we compare hydrophilic 11-Mercapto-1-undecanol and hydrophobic
1-Undecanethiol SAMs and their gold-dissolution inhibiting properties. We can
show that the intermolecular forces (hydrophobic vs hydrophilic effects)
control how SAM layers perform under oxidative conditions. Specifically, using
\textit{in situ} electrochemical AFM and a scanning-flow cell coupled to an
ICP-MS a complementary view on both corrosion resistance, as well as on changes
in surface morphology/adhesion of the SAM is possible. Protection from
oxidative dissolution is higher with hydrophobic SAMs, which detach under
micelle formation, while the hydrophilic SAM exhibits lower protective effects
on gold dissolution rates, although it stays intact as highly mobile layer
under anodic polarization. The developed multi-technique approach will prove
useful for studying the interfacial activity and corrosion suppression
mechanism of inhibiting molecules on other metals and alloys.
