Microencapsulation, self-healing polymers

Kirkby, E.L., Michaud, V.J., MSnson, J.A.E., Sottos, N.R., and White, S.R. (2009) Performance of self-healing epoxy with microencapsulated healing agent and shape memory alloy wires. Polymer, 50, 5533-5538. 

Self-healing is often used in a broader sense, to mean reconstruction of the entire polymer instead of just its surface. A relevant example here is a PDMS elastomer that contains microencapsulated PDMS resin and microencapsulated cross linker. If this type of PDMS is damaged, both capsules rupture and the newly formed elastomer mends the damaged area. 

The present work covers a variety of self-healing motifs, systems, and chemistries. The first example of a practical fully self-contained self-healing system based on microencapsulated dicyclopentadiene and Grubbs catalyst particles embedded in an epoxy matrix,) 16) formed the basis for further research on similar self-healing systems and thus forms the basis for the discussion presented herein. For all chemistries discussed, the efforts in compartmentalization of the reactants, evaluation of self-healing performance, and testing in relevant applications such as reinforced polymer composites and coatings are presented. 

Fig. 1. Original microencapsulation-based self-healing system. Microencapsulated dicy-clopentadiene is embedded in an epoxy resin containing Grubbs catalyst which is capable of polymerizing the dicyclopentadiene. A propagating crack ruptures the microcapsules causing DCPD to be released into the crack plane where it comes in contact with and reacts with catalyst to form a polymer that bonds the crack hices and restores structural continuity.

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