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Prof. Feng Shi’s team published a research paper in ‘Angewandte Chemie International Edition’

Prof. Feng Shi’s team published a research paper in ‘Angewandte Chemie International Edition’

Abstract:

Flexible circuit is a revolutionary technology to assemble electronic circuits on flexible substrates for advanced products of flexible displays, flexible sensors, etc. However, one bottleneck problem in practical uses of flexible circuit is the high risk of cracks and conductivity failure caused by frequent bending, stretching and possible scratching. Currently, several strategies have been proposed for conductivity restoration including self-healing based on dynamic chemistry preloading of microcapsules containing conductive matters, etc. These innovative strategies have brought ‘smart’ features to flexible circuits, i.e. the circuits self-heal upon being damaged. However, these strategies have some restrictions under certain application conditions, such as dependence of healing ability on crack depth, low mechanical strength as a compromise of using reversible interaction, limited healing times, low compatibility with existing fabrication of flexible circuits, etc. Therefore, developing new methods for conductivity restoration of flexible circuits is urgent to address the above problems to facilitate practical uses of flexible electronics.

Recently, Prof. Feng Shi’s team, together with Prof. Bin Dong’s team from Soochow University published a research paper titled ‘A Photowelding Strategy for Conductivity Restoration in Flexible Circuits’ in an international famous journal Angewandte Chemie International Edition’. The paper

applied light-driven micropumps based on photocatalytic reactions to conductivity restoration of flexible circuits (defined as photowelding strategy). A thin PEN layer was pre-deposited on top of a circuit without disturbance to the circuit. Once cracks occurred, they immersed the circuit into a suspension of healing agents and irradiate the crack; the resulted electroosmosis effect generated by the diffusion of photocatalytic products (H+ and ·O2-) could gather healing particles at the crack to recover conductivity. Because healing agents are externally accessible and photocatalyst is not consumed, they could heal cracks for many times. The minimum distance between adjacent conductive and broken lines reaches 100 μm for successful repair, the smallest width of healable crack is 10 μm, and a 300 μm cut is healed in 8 min under a 1.2 W/cm2 irradiation. Even with a protective layer on circuits, in situ healing is still possible. The author envisions this photowelding strategy may exploit a promising application of light-driven micropumps and photocatalysis in conductivity restoration of flexible circuits due to advantages of being independent on crack depth and storage of healing agents, cost-effective, compatible with existing fabrication of flexible electronics.

Figure 1. The photowelding strategy. Schematic illustration, microscopic photos (insets) and LED bulb states of the a,b) as-prepared, c,d) damaged and e,f) repaired model flexible circuit. g) Resistance changes during the connection-disconnection-reconnection process. h) Top and i) side view SEM images of the PS@Au microparticle aggregation in the cracked area.

Figure 2. Underlying mechanism of the photowelding method. (a) Under photoirradiation, H+ and ·O2- are generated. (b) H+ diffuses faster than ·O2-, which induces an inward electrical field (c), causing electro-osmotic flow (inset in c) and moving PS/Au microparticles toward the irradiation center. (d) PS/Au microparticles aggregate near the illumination center.

Figure 3. (a-c) Schematics, (d) sensitivity changes and (e) flexibility test results demonstrating the reparation of the flexible sensing device, insets in (e) indicating the states of the repaired flexible sensor. Ammonia gas: 50 ppm.

Summary

    In this paper, the author developed light-driven micropumps based on photocatalytic reactions to conductivity restoration of flexible circuits, this strategy is precise and controllable to repair local circuit damage without disturbing nearby functional parts. Because this photowelding is proven to heal circuits even under protective encapsulation coating or specific functions of certain sensing flexible devices with crack depth independent healing capability, good repeatability and compatibility with the existing fabrication strategy, we envision its promising future in practical uses of repairing conductive failure of flexible electronics, especially at microscale.

Yunyu Sun, doctor student, is the first author of the paper. Prof. Feng Shi and Prof. Bin Dong are the corresponding authors.

Article information: (A Photowelding Strategy for Conductivity Restoration in Flexible Circuits. Angew. Chem. Int. Ed. 2019, DOI: 10.1002/anie.201909965.)

The original link: https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201909965

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