Understanding the role of trigger signal spreading, release rate of suitable active agents and their transport rate for optimal healing in extrinsic self-healing materials

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In the frame of the SPP1568, we have developed new corrosion-responsive self-healing materials based on redox-responsive nanocapsules, i.e. materials that released healing substances upon onset of the corrosion signal, and demonstrated their performance as anticorrosion coating for zinc. We have learnt from our experience that the performance of extrinsic self-healing materials is critically dependent on the signal spreading, the release rate of the active agents, and their transport velocity to the defect site. The aim of the current project is to fundamentally investigate this relationship in order to be able to design optimal self-healing materials. This will be done by systematically varying the chemical nature and morphology of the nanocontainers to control the release rate and the nature of the coating to influence the signal spreading,- on the one hand. On the other hand, the transport rate and the healing velocity will be controlled by the chemical nature of the self-healing agents. The performance of the self-healing materials for anticorrosion will be investigated by state of the art characterization techniques such as the scanning Kelvin probe spectroscopy (SKP). The dependence of self-healing performance on signal spreading, release of the active agents and their transport rate to the defect site is a very general problematic for all extrinsic self-healing materials that is material independent. For instance, in the first example of extrinsic self-healing materials shown by White et al., the signal spreading was the crack propagation while the healing velocity was given by the combination of monomer transport, size and concentration of the containers, and kinetics of the self-healing reaction. Therefore, it is also the goal of the project to apply the gained knowledge to other systems developed by other groups active in the SPP1568, to draw general conclusions that are valid for the entire field of extrinsic self-healing materials.