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 [1].

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.

1.
Muglali, M. I.; Erbe, A.; Chen, Y.; Barth, C.; Koelsch, P.; Rohwerder, M.: Modulation of electrochemical hydrogen evolution rate by araliphatic thiol monolayers on gold. Electrochimica Acta 90, pp. 17 - 26 (2013)
2.
Azzam, W.; Bashir, A.; Biedermann, P. U.; Rohwerder, M.: Formation of highly ordered and orientated gold islands: Effect of immersion time on the molecular adlayer structure of pentafluorobenzenethiols (PFBT) SAMs on Au(111). Langmuir 28 (27), pp. 10192 - 10208 (2012)
3.
Muglali, M. I.; Bashir, A.; Terfort, A.; Rohwerder, M.: Electrochemical investigations on stability and protonation behavior of pyridine-terminated aromatic self-assembled monolayers. Physical Chemistry Chemical Physics 13 (34), pp. 15530 - 15538 (2011)
4.
Bashir, A.; Azzam, W.; Rohwerder, M.; Terfort, A.: Polymorphism in self-assembled terphenylthiolate monolayers on Au(111). Langmuir 29 (44), pp. 13449 - 13456 (2013)
5.
Muglali, M. I.; Bashir, A.; Birkner, A.; Rohwerder, M.: Hydrogen as an optimum reducing agent for metallization of self-assembled monolayers. Journal of Materials Chemistry 22 (29), pp. 14337 - 14340 (2012)
6.
Muglali, M. I.; Liu, J.; Bashir, A.; Borissov, D.; Xu, M.; Wang, Y.; Wöll, C. H.; Rohwerder, M.: On the complexation kinetics for metallization of organic layers: Palladium onto a pyridine-terminated araliphatic thiol film. Physical Chemistry Chemical Physics 14 (14), pp. 4703 - 4712 (2012)
7.
Özkanat, Ö.; Salgin, B.; Rohwerder, M.; De Wit, H. J. H. W.; Mol, J. M. C.; Terryn, H. A.: Interactions at polymer/(oxyhydr)oxide/ aluminium interfaces studied by Scanning Kelvin Probe. Surface and Interface Analysis 44 (8), pp. 1059 - 1062 (2012)
8.
Özkanat, Ö.; Salgin, B.; Rohwerder, M.; Mol, J. M. C.; De Wit, H. J. H. W.; Terryn, H. A.: Scanning Kelvin probe study of (Oxyhydr)oxide surface of aluminum alloy. The Journal of Physical Chemistry C 116 (2), pp. 1805 - 1811 (2012)
9.
Salgin, B.; Özkanat, Ö.; Mol, J. M. C.; Terryn, H. A.; Rohwerder, M.: Role of surface oxide properties on the aluminum/epoxy interfacial bonding. The Journal of Physical Chemistry C 117 (9), pp. 4480 - 4487 (2013)
10.
Senöz, C.; Borodin, S.; Stratmann, M.; Rohwerder, M.: In-situ detection of differences in the electrochemical activity of Al2Cu IMPs and investigation of their effect on FFC by scanning Kelvin probe force microscopy. Corrosion Science 58, pp. 307 - 314 (2012)
11.
Senöz, C.; Rohwerder, M.: Scanning Kelvin probe force microscopy for the in situ observation of the direct interaction between active head and intermetallic particles in filiform corrosion on aluminium alloy. Electrochimica Acta 56 (26), pp. 9588 - 9595 (2011)
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