Material that can Heal Itself

Image © ACS Nano 2020, 14, 9, 11442–11451

The advent of highly deformable and healable electronics is exciting and promising for next-generation electronic devices and the search have hyped in recent years. Among several potential energy harvesting device, self-healable triboelectric nanogenerators serve as promising candidates based on the combination of the triboelectric effect, electrostatic induction, and self-healing action, however they also have issues among which one is its integration procedure. Majority of self-healable triboelectric nanogenerators have been devised with weak polymeric networks that are healed with reversible supramolecular interactions or disulfides which results in poor mechanical properties and low resistance to creeping. Group of research were searching for solution of this issue; among one was a team from Canada and South Korea. 

Triboelectric nanogenerator (TENG) is a newly developed technique for harvesting mechanical energy from ambient environment with sparkly high output and extremely flexible structural designs.

The team demonstrated the integration of mechanically strong and self-healable poly(hindered urea) (PHU) network in the fabrication of effective TENGs. The designed network is flexible and showed greater mechanical property which is capable of self-healing quickly and repeatedly as well as being reprocessable under mild conditions, enabling the recovery of triboelectric performances after the complete healing of the damaged surfaces.

TENG converts mechanical stimulus to electrical signals through the combination of triboelectric effect and electrostatic induction, first came into highlight in 2012. This displayed higher output performance compared to the other nanogenerator devices and it also possesses tremendous benefits including simple design structure, low cost, high conversion efficiency, good friction energy, and environmental friendliness.

However prominent, the major issue of conventionally designed TENGs involves the failure of their self-charging power and the suppression of their output performance and lifetime. Thus resultant SH-TENGs suffer from poor mechanical properties and low creeping resistance. This output made devices worsen for robustness and durability once they are damaged under frequent mechanical impact during repeated operation cycles. 

Several solution methods also exists; the development of vitrimeric polymers cross-linked with reversible covalent bonds typically through disulfide, boronic ester, and imine chemistries but these SH-TENGs did not solved lower performance problem.

Here, the team reported a self-healable triboelectric nanogenerators (SH-TENGs) built with dynamic and reprocessable PHU networks. The fabrication approach is based in the synthesis of a four-arm star-hindered amine (T-NH). Then formed network films were characterized for void-filling and self-healability, mechanical and viscoelastic properties, and processability. The result were promising compared with the reported healable TENGs. Furthermore, the material exhibited a rapid recovery of scratches and thus TENG performance upon excellent self-healing.

These results offer the versatility of the approach toward the development of advanced TENG materials with great triboelectric output as well as excellent self-healability and processability to increase their lifetime and preserve fossil fuels. Promisingly, this approach can be expanded to other energy-harvesting applications including artificial skins, flexible sensors, nanorobotics, and portable/wearable devices.

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