Elementary steps of electrochemically driven de-adhesion of organic coatings
Two main approaches are used in the group for studying the fundamental steps of delamination. One is to apply Scanning Kelvin Probe Force Microscopy (SKPFM) for studying microscopic and submicroscopic processes during delamination, the other is to investigate the effect of modifications of the surface oxides and/or the functionality of the organic coating on the delamination behaviour. The latter is mainly done by investigating the effect of well characterised self-assembled monolayers. In cooperation with Prof. Wöll (KIT) and Prof. Terfort (Univ. of Frankfurt) our investigations on oxygen reduction at self-assembled thiol monolayer films are extended on a broader base of various aromatic thiol molecules. In order to establish the targeted structure-reaction correlation on the molecular and nanoscopic scale a thorough characterisation of the monolayers is carried out [1-4].
The investigations on monolayer stability provided also extremely interesting results on hydrogen evolution at organic layers and on metallization of self-assembled films. The hydrogen evolution reaction seems to be enhanced at the first stages of cathodic monolayer desorption, which is due to the prevailing molecular order of the film directly after desorption .
Side results of this work were the development of a novel approach for optimizing the complexation of metal cations on self-assembled monolayers and their electro-less reduction by hydrogen which provides metal monolayers of superior properties [5,6].
The effect of different pre-treatments on the interface with different coatings was studied in detail for aluminium [7-9]. SKPFM was very successfully applied on filiform corrosion and it could be shown by performing the experiment under repetitive gas change conditions (between air and nitrogen) that cathodic delamination at the head of the corrosion filaments can play a crucial role in coupling the anodic head with micron size active cathodic sites at the interface [10, 11].
Main focus of current research is the quantitative measurement of reaction rates at buried interfaces. More details will be provided soon.