Autonomic healing mechanism

Microcrack formation and crack propagatiOTi are a common cause of material failure. To overcome this problem, supramolecular polymer networks have been developed that can self-heal on the basis of the dynamic nature of their reversible cross-links [268]. The healing can either occur in an autonomous fashion or upmi exposure to an external stimulus such as heat, light, pressure, or mechanical stress. 

A prototypical autonomous biological device is a Vibrio cholerae bacterium that packs the ability to move, sense, target, adapt, and release active substances into just a few cubic centimeters. An example of a smart biological material, muscle, which is composed of autonomous systems, is hierarchically assembled from microscopic subunits, has the ability to exehange information with the enviromnent via electrical and mechanical stimuli, and incorporates energy-conversion modules and self-healing abilities. 

Reversible supramolecular interactions in polymers can be achieved via several mechanisms, such as hydrogen bonding, exemplified by the ure-idopyrimidinone unit (Bosman et al, 2004 Montarnal et al, 2009), metal coordination chemistry (Fiore et al, 2011 Kumpfer et al, 2010), or k-k stacking, such as that seen with triphenylene units (Buratini et al, 2009). These materials can heal autonomously in a few cases, but in most cases also need stimuli for their healing action such as temperature or pressure. 

For primers with self-healing and corrosion inhibitive properties, it is desirable to have one component to inhibit corrosion of the underlying metal and a second component to repair the polymer coating. These individual components can be multifunctional or multistep. For the protection of metals, many paint systems consist of an inhibitive primer and a topcoat. In case the coating is mechanically damaged or local delaminations are present, the repair function is usually achieved via release of the inhibitors from the inhibitive primer, whereby the corrosion performance of the underlying metal surface benefits from autonomous surface recovery processes by the precipitation of stable inhibitor compounds at cathodic and/or anodic sites. 

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