Functional Surfaces, Interfaces
The development of coatings for corrosion protection within the department focuses mainly on the application of conducting polymers and particle modified zinc coatings.
It was found that in principle three different cases exist for metal coatings based on conducting polymers:
- enhanced corrosion where the conducting polymer oxidises the metal and the conducting polymer in turn is re-oxidised by oxygen from the air;
- a passive interface with electronic contact between metal and conducting polymer, which is the targeted situation as it allows a corrosion triggered release of self-healing agents; and
- a situation where electronic contact between metal and conducting polymer is lost, leading to Fermi level misalignment between these two.
The first and the last cases have both to be avoided. A simple SKP based screening method was developed for characterising the different coating systems in regard to these three cases and first models are proposed to explain the underlying mechanisms [1]. This will play an indispensable role for developing reliable coating systems.
The storage of active substances inside the zinc (alloy) coating is considered to be of central importance for ensuring self-healing coating systems that will be fully operative even after long term exposures: the more reactive components, such as catalysts initiating polymerisation of monomers released from the organic coating, will be safely stored in the zinc (alloy) coating that is impermeable for water or oxygen. The synergy between agents stored in the zinc coating and an organic or inorganic-organic hybrid coating is also the central concept of the MPG-FHG cooperative project on active corrosion protection (ASKORR) carried out together with MPIP, SIC and IAP. One of the main problems for the storage of capsules in zinc, the difficulty to electrodeposit water dispersible capsules into zinc coatings, was successfully overcome [2].
A molecular level understanding of interaction forces and dynamics between asymmetric opposing surfaces in water plays a key role in the utilization of molecular structures for functional and smart surfaces and coatings. To quantify interaction forces and binding dynamics between opposing surfaces in terms of their chemical and molecular design we developed a novel surface forces apparatus experiment, utilizing molecularly smooth self-assembled monolayers (SAMs). Varying the SAM headgroup functionality allowed us to quantitatively identify which interaction forces dominated between the functionalized surfaces and a surface coated with a precisely controlled number density of short-chain, amine end-functionalized polyethylene-glycol (PEG) polymers. We could directly quantify and distinguish (a) specific bindings, (b) steric effects of polymer chains and, (c) adhesion of the polymer backbone, all as a function of the solution pH. Combined with novel synthetic approaches this newly developed concept will allow a very accurate molecular quantification of binding interactions between arbitrary chemical functionalities, and polymer backbones with surfaces [3].