Liquid monomer-filled microcapsules are disseminated in an epoxy matrix similar to those seen in polymeric composites of Self-Healing Materials. The epoxy contains a catalyst that causes the monomer that is enclosed to polymerize. The micro-capsules are released when a crack appears in the cured material. The monomer is drawn into the crack by capillary action, where it is exposed to the catalyst and causes polymerization. The two crack faces are joined by the polymerized substance. As a result, the material repairs itself after being damaged.
Although this fundamental approach seems very straightforward, polymer chemists face some enormous difficulties with it.
· The monomer must have a long shelf life and be compatible with an encapsulating process.
· The epoxy matrix and the surrounding conditions in which the sample is prepared must not harm the catalyst.
· The subsequent polymerization must to happen quickly and at room temperature.
· The random rupture of microcapsules on the crack face leads to inaccurate control of the stoichiometry, hence the reaction needs to be somewhat insensitive to the monomer: catalyst ratio.
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