Speaker
Mr
Matic Poberznik
(Jozef Stefan Institute)
Description
In the search for new ways of how to achieve efficient corrosion inhibition, the knowledge about the interaction between the substance acting as an inhibitor and the metallic substrate is useful. To this end, Density Functional Theory (DFT) based modeling is a convenient tool for providing new insights, hence it has been utilized to complement the experimental characterization of several molecules as potential corrosion inhibitors of aluminium in chloride media [1]. Two basic constituents of the archetypal structure of corrosion inhibitor—the reactive anchor group, which interacts with the surface and the less reactive backbone, which governs lateral cohesion within the inhibitor layer—were varied in order to disentangle and scrutinize the interactions within the inhibitor–substrate system.
The phosphonic, silanol, carboxylic, imidazole, and thiol functional groups were chosen as model anchors. Adsorption of inhibitors was modeled via two different mechanisms, i.e., plain (non-dissociative) adsorption and a dissociative condensation mechanism, but strong molecule–surface bonds are formed only in the latter mode. This mode is found to be considerably exothermic for the phosphonic and silanol anchor group, marginally exothermic for the carboxylic anchor group, and endothermic for the thiol and imidazole anchor groups. This indicates that molecules containing the phosphonic and silanol anchor groups will “stick” to the surface regardless of the backbone, whereas for the carboxylic anchor group additional stabilization is required for a stable layer to form and such stabilization can be provided by a backbone. In contrast, the thiol and imidazole groups are unlikely to “stick” to the surface. These predictions conform well with the experimental measurements performed in our groups [1].
Since additional stabilization is required for the carboxylic anchor group, it was chosen as a representative anchor while the length and type of backbone was varied. Alkyl and perfluoroalkyl backbones of lengths ranging from 2 to 17 carbon atoms were considered. In order to maximize the lateral cohesive interactions within the adsorbed inhibitor layer both types of chains were found to be tilted with respect to the surface normal. For the bulkier fluoroalkyl chains the tilting angle was found to be smaller. An additional effect of tilting is that it increases the effective coverage, preventing aggressive species from accessing the substrate.
This work is a part of M-ERA.NET project entitled “COR_ID: Design of corrosion resistant coatings targeted for versatile applications”. The financial support provided by MESS (Ministry of Education, Science and Sport of Republic of Slovenia) and ANR (The French National Research Agency) is acknowledged.
[1] I. Milošev et al., in preparation.
Primary author
Mr
Matic Poberznik
(Jozef Stefan Institute)
Co-author
Dr
Anton Kokalj
(Jožef Stefan Institute)
