Self-Healing Material Synthesis

Self-healing materials were first observed as early as the 1970s, which refer to the artificial or synthetical substances that have the built-in ability to automatically repair damages to themselves without any external diagnosis or human intervention. They have received extensive attention from various fields due to their extra security, increased lifetime, low incidence of system failures, and decreased maintenance and cost requirements. To develop an ideal self-healing material, two important points need to be met, including (i) an efficient cross-linking reaction and (ii) healing at room temperature or even below^[1].

Click chemistry is a powerful technique that has been used as a cross-linking reaction mainly because it is very simple and effective. It is also highly effective in self-healing material synthesis.

Applications

• Self-healing material synthesis by CuAAC click reaction

Nanocomposites with self-healing ability provide new guidelines for strong, sustainable, and durable materials. Akhan et al^[2]. developed autonomously self-healing UV-cured polyurethane graphene oxide nanocomposite coatings by copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction (Scheme 1). Low molecular weight tetra-arm azide was successfully capsulated within poly (vinyl formal) capsules. Alkyne functional graphene-oxide reinforced nanocomposites containing azide microcapsules were prepared through photo-polymerization. Results suggested the self-healing ability and anti-corrosion properties of nanocomposites were improved by this method.

Scheme 1. The synthesis of self-healing UV-cured polyurethane graphene oxide nanocomposite coatings.

• Self-healing material synthesis by DA click reaction

The lifetimes of self-healing hydrogels has the potential to improve stress-induced deformation and propagation of cracks. Shao and co-workers reported a facile and efficient strategy to fabricate a nanocomposite hydrogel via Diels-Alder (DA) click reaction between cellulose nanocrystal and poly (ethylene glycol) (CNC-PEG) (Scheme 2). Self-healing capability of CNC-PEG nanocomposite hydrogels assessed by tension tests was found to be as high as 78%^[3], which would shed insight into designing reusable and renewable polymeric hydrogels.

Scheme 2. Synthesis route to the self-healing CNC-PEG nanocomposite hydrogels (the inserted
images are the CNC aqueous solution and its TEM images, bar = 500 nm).

What Can We Do?

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References

1. Guimard, N.K.; et al. Current trends in the field of self-healing materials. Chinese Journal of Polymer Science. 2012, 213: 131-143.
2. Akhan, S.; et al. Polyurethane graphene nanocomposites with self-healing properties by azide-alkyne click reaction. Materials Chemistry and Physics. 2020, 254: 123315.
3. Shao, C.; et al. A self-healing cellulose nanocrystal- poly (ethylene glycol) nanocomposite hydrogel via Diels-Alder click reaction. ACS Sustainable Chemistry & Engineering. 2017, 5(7): 6167-6174.